STRUCTURE magazine | April 2017 by structuremag

A Joint Publication of NCSEA | CASE | SEI

STRUCTURE

April 2017 Concrete Inside: Fire Station #27 Dallas, Texas

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TRANSFORMING THE WAY THE WORLD WORKS

CONTENTS Columns/Departments EDITORIAL

7 Paying the Debt to Our Profession By David W. Mykins, P.E. CONSTRUCTION ISSUES

8 How Installation Torque Can Affect Expansion Anchors By Richard T. Morgan, P.E.

Cover Feature

36 Dallas Fire Station #27 By Akshai Ramakrishnan, P.E. The goal of this multi-story fire station upgrade was to provide a modernized facility in a growing urban environment. That “urban environment” meant dealing with extreme site constraints that resulted in several unique solutions.

STRUCTURAL SUSTAINABILITY

13 Zinc Coated Reinforcing Steel By Mike Stroia STRUCTURAL SPECIFICATIONS

INSIGHTS

16 Residential Wood Deck Design

50 Building Official Expectations

By John “Buddy” Showalter, P.E. and

Features

Loren Ross, P.E.

By Chris Kimball, S.E., P.E.

28 ALBINA YARD

STRUCTURAL REHABILITATION

BUILDING BLOCKS

By Blake Patsy, P.E., S.E. Exposed mass timber structural framing and cross-laminated timber floor and roof panels make the Albina Yard structure a unique story in the “forest to frame” trend. Entirely composed of mass timber elements, this is the first building of its kind in the U.S.

20 Cathodic Protection of Infrastructure

52 Environmental Product Declarations By J. Kenneth Charles, III and

By Paul Noyce and Gina Crevello

Robert C. Paul, P.E. STRUCTURAL SYSTEMS

26 How Beauty Beat Brawn

CASE BUSINESS PRACTICES

55 Foundations for Risk Management – They Still Matter

By Jeremy Herauf STRUCTURAL DESIGN

By Brent White, P.E., S.E.

38 Seismic Design of Nonbuilding Structures By J. G. (Greg) Soules, P.E., S.E. P.Eng., SECB HISTORIC STRUCTURES

42 Lachine Rapids Bridge By Frank Griggs, Jr., D.Eng., P.E. PROFESSIONAL ISSUES

46 Overall Career Satisfaction, Development, and Advancement By Angie Sommer, S.E. and Rose McClure, S.E.

IN EVERY ISSUE 6 Advertiser Index 62 Resource Guide (Engineered Wood Products) 56 NCSEA News 58 SEI Structural Columns 60 CASE in Point

Publication of any article, image, or advertisement in STRUCTURE® magazine does not constitute endorsement by NCSEA, CASE, SEI, C 3 Ink, or the Editorial Board. Authors, contributors, and advertisers retain sole responsibility for the content of their submissions.

STRUCTURE magazine

April 2017

32 ECONOMICAL LONG-SPAN HIGH-RISE By Cary Kopczynski, P.E., S.E. and Joe Ferzli, P.E., S.E. A 25-story apartment tower fostering upscale urban living is not necessarily a unique circumstance today. However, do it with no internal columns to create expansive floor plans and you have a structural solution worth reading about.

On the cover Dallas Fire Station #27 is a unique multi-story facility, rebuilt and composed of a concrete frame with the energy efficiency to meet LEED standards. The real challenge was fitting the upgraded 23,000-square-foot fire station on an existing land-locked site of 18,500 square feet. See feature article on page 36.

ADVERTISER INDEX

PLEASE SUPPORT THESE ADVERTISERS

American Concrete Institute ................. 12 Anthony Forest Products Co. ................ 31 Atlas Tube ............................................. 53 BASF..................................................... 41 Bluebeam Software .................................. 4 Canadian Wood Council ....................... 19 Cast ConneX........................................... 2 CTP, Inc................................................ 47 Dlubal Software, Inc. ............................ 43 Fyfe ....................................................... 17 Geopier Foundation Company.............. 11 Hohmann & Barnard, Inc. .................... 48 ICC – Evaluation Service ...................... 45 Integrated Engineering Software, Inc..... 54

KPFF Consulting Engineers .................... 6 Larsen Products Corp. ........................... 44 LNA Solutions ...................................... 24 MAPEI Corp......................................... 25 Rhino Carbon Fiber .............................. 23 RISA Technologies ................................ 64 Simpson Strong-Tie......................... 15, 35 Strongwell ............................................. 34 StructurePoint ....................................... 63 Super Stud Building Products, Inc........... 9 Trimble ................................................... 3 USG Corporation ................................. 49 V2 Composites...................................... 39 Weyerhaeuser ........................................ 51

STRUCTURE

ADVERTISING ACCOUNT MANAGER INTERACTIVE SALES ASSOCIATES sales@STRUCTUREmag.org Eastern Sales Chuck Minor 847-854-1666 Western Sales Jerry Preston 480-396-9585

EDITORIAL STAFF Executive Editor Alfred Spada aspada@ncsea.com Editor Christine M. Sloat, P.E. publisher@STRUCTUREmag.org Associate Editor Nikki Alger publisher@STRUCTUREmag.org Graphic Designer Rob Fullmer graphics@STRUCTUREmag.org Web Developer William Radig webmaster@STRUCTUREmag.org

Erratum

EDITORIAL BOARD Chair Barry K. Arnold, P.E., S.E., SECB ARW Engineers, Ogden, UT chair@structuremag.org

In the March 2017 Technology article, Impacts on the Build Environment, Figure 3 (page 23) shows the epicenter of an earthquake as 9 kilometers deep. That label should have been hypocenter or focus. The epicenter of the quake is on the surface above the focus. The online version of this article contains a corrected graphic.

Jeremy L. Achter, S.E., LEED AP ARW Engineers, Ogden, UT Erin Conaway, P.E. SidePlate Systems, Phoenix, AZ John A. Dal Pino, S.E. FTF Engineering, Inc., San Francisco, CA Linda M. Kaplan, P.E. TRC, Pittsburgh, PA Dilip Khatri, Ph.D., S.E. Khatri International Inc., Pasadena, CA Jessica Mandrick, P.E., S.E., LEED AP Gilsanz Murray Steficek, LLP, New York, NY Brian W. Miller Davis, CA

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Mike Mota, Ph.D., P.E. CRSI, Williamstown, NJ Evans Mountzouris, P.E. The DiSalvo Engineering Group, Ridgefield, CT Greg Schindler, P.E., S.E. KPFF Consulting Engineers, Seattle, WA Stephen P. Schneider, Ph.D., P.E., S.E. BergerABAM, Vancouver, WA John “Buddy” Showalter, P.E. American Wood Council, Leesburg, VA C3 Ink, Publishers A Division of Copper Creek Companies, Inc. 148 Vine St., Reedsburg WI 53959 Phone 608-524-1397 Fax 608-524-4432 publisher@structuremag.org

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April 2017

April 2017, Volume 24, Number 4 ISSN 1536-4283. Publications Agreement No. 40675118. Owned by the National Council of Structural Engineers Associations and published in cooperation with CASE and SEI monthly by C3 Ink. The publication is distributed free of charge to members of NCSEA, CASE and SEI; the non-member subscription rate is $75/yr domestic; $40/yr student; $90/yr Canada; $60/yr Canadian student; $135/yr foreign; $90/yr foreign student. For change of address or duplicate copies, contact your member organization(s) or email subscriptions@STRUCTUREmag.org. Note that if you do not notify your member organization, your address will revert back with their next database submittal. Any opinions expressed in STRUCTURE magazine are those of the author(s) and do not necessarily reflect the views of NCSEA, CASE, SEI, C3 Ink, or the STRUCTURE Editorial Board. STRUCTURE® is a registered trademark of National Council of Structural Engineers Associations (NCSEA). Articles may not be reproduced in whole or in part without the written permission of the publisher.

Editorial

Paying new trends, new the techniques Debtandtocurrent Our industry Profession issues By David W. Mykins, P.E., Chair CASE Executive Committee

few years ago, shortly after I had moved into our founding partner Roger’s office, I sat down to start my day. As I was looking at my busy calendar (meetings, reviews, financials, etc.), I noticed a small piece of paper taped to the wall where Roger might have seen it every day as he sat down at his computer. On it was this simple message, “All professionals owe a debt of time and talent to the enhancement of their profession.” For a moment, I stopped focusing on the company’s bottom line and began to recall the many ways in which he embraced this message and encouraged the rest of us to do the same. Throughout his career, I observed him not just becoming a member of engineering organizations, but volunteering for committees, serving on boards, and, in many cases, eventually leading these organizations. I also recalled the way that he inspired others to follow his lead and contribute to the enhancement of the engineering profession. So I thought I would explore the opportunities for all of us to embrace this message. There are so many ways that engineers can give a little something back to the profession. Perhaps the most obvious is to join one of the state or local chapters of the major engineering organizations, like NCSEA, SEI, or CASE. Many of these groups have regular meetings and local committees or task groups that are always looking for fresh new ideas and helping hands. This is a great place to start and explore how this profession excites and inspires you. But don’t just attend; the real value of membership is realized when you become involved. Another avenue for engineers to help the profession is by recruiting future generations of engineers. There have been many articles describing the loss of labor expected to occur as the baby boomers begin to retire. It is forecast that 50% of the entire workforce will retire by 2020 and the labor pool behind them is not large enough to replace them. That means there is likely to be a shortage of workers across every sector. To help reduce the effects of this for engineering, we can become proactive in recruiting the best and brightest of our young people by encouraging them to enroll in STEM tracks in middle and high school. There are STEM summer camps offered by local public schools to promote careers in engineering and the sciences that would love to have practicing professionals give short presentations to help get young people excited about these career opportunities. It’s easy and very rewarding to get involved at this level. Volunteer organizations are another opportunity for engineers to give back, by donating their time and talent toward the betterment of others. Across the country, there are active chapters STRUCTURAL of Engineers Without Borders ENGINEERING INSTITUTE (EWB) and similar faith-based groups. Organizations like EWB help communities in developing a member benefit

STRUCTURE

countries around the world meet basic human needs like clean water, sanitation, and safe structures. Often these projects are more challenging and require greater creativity than we experience designing projects in the developed world. Many of these projects are in remote locations with very limited physical resources and a mostly unskilled labor force. The innovation needed to provide safe, simple solutions that can be easily implemented is both challenging and rewarding for those who choose to volunteer. Engineers can also contribute in meaningful ways to their communities by volunteering time and talent to charitable organizations. These groups can benefit from the unique skills and expertise that engineers possess. An obvious choice for structural engineers is Habitat for Humanity. But active involvement in any charitable organization enhances the profession. Providing an example of selfless service in support of others elevates the level of respect for the profession in the eyes of those who observe it. It can also be very personally rewarding to know that you are making a difference in the lives of people who are less fortunate than you. Most of us have someone in our family or extended family with a special need or illness, or we know someone who does. It is often more fun and meaningful to attach a personal connection to your choice of charitable organization to support. I can guarantee how rewarding giving back to the engineering profession, future engineers, your community, and even the world can be. But also, you never know, your company’s bottom line might also be rewarded by the relationships and connections you make along the way. It’s hard to believe that my two years as Chairman of CASE are coming to a close. I have been honored and humbled to have had the opportunity to share my thoughts through the many editorials I have written for STRUCTURE magazine. I hope I have stimulated some thought and discussion on the topics I have advanced, and contributed in some small way to the dialogue in our profession. I will be turning over the reins of leadership in CASE to the capable hands of Corey Matsuoka of SSFM International, Honolulu, Hawaii. In closing, I encourage you all to think of structural engineering not as a job, but as a responsibility and a lifelong passion.▪

STRUCTURE magazine

David W. Mykins is the President and CEO of Stroud, Pence & Associates, a regional structural engineering firm headquartered in Virginia Beach, VA. He is the current Chair of the CASE Executive Committee. He can be reached at dmykins@stroudpence.com.

April 2017

ConstruCtion issues

(a)

(b)

discussion of construction issues and techniques Figure 1. a) Hilti Kwik Bolt-TZ Anchor; b) Hilti HSL-3 Anchor.

ost-installed expansion anchors are used to attach fixtures to concrete and masonry. Expansion anchor types include torque-controlled anchors, which must be torqued to expand wedges, and displacement-controlled anchors, which require impact forces on a sleeve or plug to expand wedges. Expansion anchors that rely on torque to expand wedges are referred to as torque-controlled expansion anchors. This article discusses the importance of torque on the installation and performance of torque-controlled expansion anchors installed into concrete.

How Installation Torque Can Affect Expansion Anchors By Richard T. Morgan, P.E.

Why Torque Expansion Anchors?

Richard T. Morgan is the Manager for software and literature in the Technical Marketing Department of Hilti North America. He is responsible for PROFIS Anchor and PROFIS Rebar software and can be reached at richard.morgan@hilti.com.

Figure 1 illustrates the components of a torquecontrolled expansion anchor. Applying a torque to the nut activates a mechanism whereby displacement (movement) causes the wedges to expand into the concrete. This mechanism consists of a tapered mandrel that moves up through the wedges. The tapered mandrel can be a part of the bolt shank (Figure 1a), or it can be a separate assembly that threads onto the bolt shank (Figure 1b). When the wedges are expanded, a tension pre-load develops in the anchor along with a compression clamping load between the fixture and the concrete. Pre-loading reduces the amount of displacement the anchor undergoes when subjected to external tension load. Preloading also reduces anchor fatigue under cyclic loads. Clamping eliminates gaps between the fixture and concrete.

What Results from Torquing? Torquing creates a tension pre-load in the anchor and a commensurate clamping load between the fixture and the concrete. Tension pre-load and clamping load depend on several parameters: • the amount of torque applied to the anchor • the friction that develops between the nut and bolt threads • the friction between the nut and washer

April 2017

• the friction between the washer and fixture • the friction between the fixture and concrete surface • the amount of wedge expansion • the concrete compressive strength • the angle between the installed anchor and fixture surface • the elapsed time after the installation torque has been applied Figure 2 illustrates the effect an external tension load has on a torque-controlled expansion anchor. The load corresponding to pre-load in the anchor, and clamping between the fixture and the concrete, is designated Ntorque. Torquing causes the anchor to undergo a positive (i.e. tension) displacement, which is offset by a negative (i.e. compression) displacement in the concrete. The amount of pre-load, clamping, and displacement are dependent on the parameters listed above. Application of external tension load to the fixture reduces the clamping load between the fixture and concrete while adding some tension load to the anchor. Since concrete is typically stiffer in compression compared to the tension stiffness of an anchor, the additional tension load on the anchor resulting from the external tension load is minimized as long as any clamping load remains. Once the clamping load between the fixture and concrete is completely removed, any external tension load applied to the fixture acts directly on the anchor. Figure 3 illustrates the effect an external tension load has on a torque-controlled expansion anchor after the clamping load between the fixture and concrete has been removed. It is necessary to make a distinction between anchor performance in uncracked concrete versus cracked concrete. When a torque controlled expansion anchor is installed in uncracked concrete, the anchor pre-load created by torquing will decrease over time. Relaxation within the interface between the nut and bolt threads and relaxation of the stressed concrete in the areas adjacent to the expansion wedges contribute to this decrease. The anchor pre-load decrease occurs rapidly at first, sometimes within minutes after the initial torque has been applied. The decrease continues over several hours, then days, eventually reaching

anchor pre-load

clamping

pre-load/clamping created by torqueing (Ntorque)

loss of clamping load resulting from Nexternal

external applied tension load (Nexternal)

pre-load/clamping created by torqueing (Ntorque)

Ntorque

All tension load resulting from Nexternal acts on the anchor.

remaining clamping load resulting from Nexternal

anchor pre-load

clamping

loss of all clamping load resulting from Nexternal

displacement anchor (tension)

displacement

concrete (compression)

anchor (tension)

Figure 2. Effects of external tension load with clamping.

a plateau (e.g. 100+ days). The amount of anchor pre-load lost over this time can range between 50-60% of the initial anchor preload. Re-torquing permits some of this anchor pre-load loss to be regained. However, a loss of anchor pre-load due to relaxation will continue to occur, albeit to a lesser extent than the original loss. Re-torquing is discussed later in this article. With respect to cracked concrete conditions, torque-controlled expansion anchors

external applied tension load (Nexternal)

tension load

increase in tension load on the anchor resulting from Nexternal

concrete (compression)

Figure 3. Effects of external tension load without clamping.

can lose all of the anchor pre-load when a crack propagates to the anchor. The size of the drilled hole is effectively increased, which requires additional wedge expansion, via additional anchor displacement, to accommodate the crack. This additional wedge expansion resulting from the additional anchor displacement is referred to as follow-up expansion. Torque-controlled expansion anchor design for cracked concrete conditions requires the anchor to have ADVERTISEMENT–For Advertiser Information, visit www.STRUCTUREmag.org

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STRUCTURE magazine

April 2017

follow-up expansion capability. Therefore, it is important to select an anchor specifically qualified for use in cracked concrete. Whether cracked or uncracked concrete conditions exist, pre-load and the commensurate clamping load will decrease. Once these loads are removed, any additional external tension load applied to the fixture will cause additional anchor displacement and “lift-off” of the fixture, whereby a space develops between the

fixture and concrete surface. The tension load is now acting directly on the anchor(s). Anchoring-to-concrete strength design provisions for tension assume the loads acting on an anchorage act directly on the anchor elements, i.e., no pre-load/clamping load remains. Anchoring-to-concrete strength design provisions for shear likewise assume the loads act directly on the anchor elements, i.e., no clamping load remains. Furthermore, the clamping load that does develop from torquing an expansion anchor is not considered sufficient to design an anchorage as a slip-critical connection for resisting shear load.

What is the Result of Improper Torquing? Expansion anchors must be torqued per the values provided in the Manufacturer’s Printed Installation Instructions (MPII) to properly expand the wedges and clamp the fixture. Under-torquing results in underexpansion of the wedges, which reduces the amount of clamping developed. Once pre-load/clamping is removed from an under-torqued expansion anchor subjected to tensile loading, the anchor will displace, resulting in follow-up wedge expansion and lift-off of the fixture. An anchor group consisting of anchors that are torqued unequally during installation can have an unequal load distribution on the anchors. For example, Section 5.2.2 – Drill bit requirements in the American Concrete Institute (ACI) Standard ACI 355.2 (Qualification of Post-Installed Mechanical Anchors in Concrete) permits anchor installation at an angle up to 6 degrees from perpendicular. Anchors in a group that are installed at an excessive angle (with respect to perpendicular) will have a different tension pre-load compared to anchors in the group installed perpendicular to the surface. If this unequal load distribution on the anchors is not considered, the calculated anchorage capacity may be unconservative. A non-uniform clamping load will also develop between the fixture and concrete. Torque-controlled expansion anchors must be qualified per the International Code Council Evaluation Service (ICCES) acceptance criteria AC193 (Acceptance Criteria for Mechanical Anchors in Concrete Elements) in order to receive recognition under the International Building Code (IBC). Recognition is given in an ICC-ES evaluation report (ESR). AC193 also references ACI 355.2; Section 5.2.3 – Setting

requirements for testing in ACI 355.2 includes provisions for checking the effects of undertorquing. These provisions are given in Section 5.2.3.2.1, and are as follows: “For the reliability tests performed with reduced installation effort (Table 4.1, Test 3 and Table 4.2, Test 5), install and set the anchor with a setting torque of 0.5Tinst. Do not reduce the torque from this amount.” The parameter Tinst is defined in ACI 355.2 Section 2.2 – Notation as the “specified or maximum setting torque for expansion or pre-stressing of an anchor.” Tinst corresponds to the recommended torque value given in the MPII. Setting a torque-controlled expansion anchor with Tinst causes anchor displacement/wedge expansion and preload/clamping load to develop. Referencing the ACI 355.2 Commentary Sections R5.2.3 and R.5.2.3.1, the test provisions given in Section 5.2.3.2.1 are intended to simulate “installation error on the job site” (i.e. under-torquing) and to determine “if the anchor will still properly function if set with a torque substantially below the recommended torque.” An under-torqued expansion anchor will have under-expanded wedges. Testing per ACI 355.2 Section 5.2.3.2.1 assesses if a torque-controlled expansion anchor set with a torque less than Tinst , and after removal of any preload/clamping load, can undergo sufficient follow-up expansion to function in an acceptable manner. Over-torquing a torque-controlled expansion anchor could result in the occurrence of various failure modes. One possible failure mode is concrete splitting. The ACI 355.2 test 9.3 – Service-condition test at minimum edge distance and minimum spacing “is performed to check that the concrete will not experience splitting failure during anchor installation.” The test consists of installing two anchors in uncracked concrete at a minimum edge distance (c min) and minimum spacing (smin) established by the anchor manufacturer. Each anchor is installed with a setting torque that is greater than the smaller of (1.7Tinst) and (Tinst + 100 ft-lb). The smallest values for cmin and smin that can be achieved without splitting failure represent the minimum edge distance and minimum spacing for the anchor in both cracked and uncracked concrete. Over-torquing can also result in steel failure of the anchor, the anchor pulling through the wedges, or the entire anchor pulling out of the concrete. Torque-controlled expansion anchors must be installed in holes drilled with matched-tolerance bits. Installing an

STRUCTURE magazine

April 2017

anchor in an under-sized drilled hole can damage the wedges and inhibit wedge expansion during torquing. Installing an anchor in an oversized drilled hole results in the wedges not able to fully engage the concrete, thereby preventing them from properly expanding when the anchor is torqued or externally loaded.

How is Inspection Accomplished? The MPII for an anchor provides specified torque values. These torque values must be used when installing the anchor. The IBC requires special inspection for “materials and systems required to be installed in accordance with additional manufacturer’s instructions” (e.g. reference Section 1705, Required Special Inspections and Tests, and specifically Section 1705.1.1 Special cases in the 2015 IBC). Special inspection is intended to be an independent evaluation of the work that has been performed. The special inspector is employed by, and acts on behalf of, the owner or through the architect/engineer of record who represents the owner. The special inspector should not be employed by the contractor since this would be considered a conflict of interest. Therefore, special inspection with respect to a torque-controlled expansion anchor is a means to verify, among other things, that the anchor has been properly installed using the manufacturer’s specified torque value. The ESR will note special inspection requirements unique to an anchor. These special inspection requirements can include verification of the “tightening torque” used to install the anchor. Torquing must be performed with a properly calibrated torque wrench. This assures that the manufacturer’s specified setting torque is used, and it also helps avoid under-torquing or overtorquing of the anchor. Since the interface between the nut and bolt threads is integral to developing pre-load in the anchor, these threads should be inspected for damage or fouling before torquing, and should never be lubricated. Verifying a torque value brings up the subject of re-torquing. As previously noted, even without any external load being applied to an expansion anchor installed in uncracked concrete, the pre-load resulting from torquing tends to decrease over time due to relaxation. Expansion anchor pre-load loss in cracked concrete occurs when a crack propagates to the anchor. Re-torquing an expansion anchor is used to reintroduce a higher preload or clamping

Summary This article discussed the importance of torquing with respect to the installation and functioning of torque-controlled expansion anchors installed into concrete. Installation torque creates a tension pre-load in the anchor and

a clamping load between the fixture and concrete. A properly qualified, designed, and installed expansion anchor set with the manufacturer’s specified installation torque will function as designed. Under-torquing causes under-expansion of the wedges, which results in lower-than-intended clamping of the fi xture and increased anchor displacement when external tension loads are applied. Over-torquing can lead to concrete failure, steel failure of the anchor, or some form of anchor pullout failure.

The MPII and ESR provide specified installation torque values for an anchor. The ESR notes if the anchor is qualified for use in cracked concrete and the special inspection requirements. Special inspection of torquecontrolled expansion anchors, conducted by an approved agency acting on behalf of the owner or owner’s representative, is required by the IBC. Calibrated torque wrenches or power tools specifically designed for setting a torquecontrolled expansion anchor should be used for installation and inspection of the anchor.▪

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load. Re-torquing can also be used to re-set the anchor when the location of a fixture must be adjusted. The nut threads, anchor threads, and area under the washer should be cleaned before re-torquing if the nut is loosened or removed. When re-torquing an anchor, the re-torque value should never exceed the torque value given in the MPII. A rule of thumb is to limit the number of times an expansion anchor can be re-torqued to three times. Consult with the anchor manufacturer for guidance with respect to a particular product. ACI 355.2 Section 5.2.3.1.1 includes provisions for testing the relaxation effects on a torque-controlled expansion anchor. The recommended torque value (Tinst) given in the MPII is applied using a calibrated torque wrench. After 10 minutes, the nut is loosened and a torque of 0.5Tinst is re-applied using the calibrated torque wrench. This test simulates the loss of pre-load over the service life of the anchor and assesses if the anchor can function in an acceptable manner after relaxation has occurred. Torquing is sometimes used as a crude means of proof loading an expansion anchor to verify some level of performance and rule out gross installation errors. The use of torque to proofload an anchor is not precise because the torque-tension relationship can be highly variable from one anchor to another. A manually operated torque wrench is commonly used to install and proof-load torque-controlled expansion anchors. The published torque values of a power tool such as an impact wrench do not coincide with a manually applied torque value, and standard impact wrenches do not have the required calibration accuracy. Therefore, an impact wrench should not, as a rule-of-thumb, be used to set a torque-controlled expansion anchor. That said, technological advances by some manufacturers now permit torque-controlled expansion anchors to be set with an “adaptive torque tool” specially calibrated for setting this type of anchor.

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orrosion of steel reinforced concrete affects everyone, leading to expensive repairs and intensive maintenance programs. Budgeting of repairs and maintenance programs becomes difficult when structures do not meet their intended life cycle requirements. Corrosion of reinforcing steel in concrete structures leads to concrete failure, impacting the public with delays and detours. The Federal Highway Administration’s National Bridge Inventory records reflect that less than 16% of existing U.S. bridge decks utilize corrosion resistant reinforcing steel. Beyond bridge decks and highway infrastructure, corrosion protection of concrete reinforcement is an even smaller percentage. Preservation of assets by using zinc-coated reinforcing steel can be a cost-effective solution to improving the life cycle and durability of concrete structures. Maintenance programs often include Cathodic Protection by attaching zinc anodes to steel reinforcement to delay further damage of existing corrosion. This has proven to be an effective means of preventative maintenance in different types of structures. Results can be achieved over the lifetime of the structure without the cost of expensive rehabilitation by using zinccoated reinforcement from the beginning. With recorded installations prior to the 1960s, hot-dip galvanized reinforcement in concrete is a proven performer. Multiple case studies indicate that these mitigation techniques result in structures lasting decades. The galvanizing industry continues to innovate and expand as process technologies and market conditions improve. Hot-dip galvanized steel is a widely used coating in atmospheric conditions for automotive, transportation, construction, energy, and power markets. The use of hot-dip galvanizing in concrete can be traced back decades in different applications. Bridge decks, installed as far back as the 1970s, that are exposed to extreme conditions can be found performing well. Structures from around world, such as the Sydney Opera House, Lotus Temple in India, New York’s new NY Bridge, and Canada’s AutoRoute 40 in Montreal, have successfully used hot-dip galvanized reinforcement. In addition to traditional hot-dipped (ASTM A767) galvanizing, reinforcing bar can now also be coated

The Jesup Bridge Buchanan County, Iowa.

Structural

SuStainability 1973 hot-dip galvanized bridge deck, Athens, PA.

in a continuous process (ASTM A1094). This innovative process takes the advanced technology used in the sheet steel industry and applies it to reinforcing steel. Galvanized coatings have always provided both barrier and sacrificial protection for steel. With this technology, the bars can also be formed after coating without cracking or peeling of the zinc layer. The automated process allows the development of a pure zinc alloy rather than a zinc-iron alloy that, in heavier thicknesses, can become brittle. The continuous galvanized rebar process also provides a paintable substrate for dual coated reinforcement (ASTM A1055). The ASTM A1055 specification has been modified to allow two types of zinc alloy coatings, thermal spray (type 1) or as applied by ASTM A1094 (type 2). Zinc coatings passivate very quickly when exposed to fresh concrete, which enhances the long-term corrosion protection of the galvanized reinforcements during years of service. The initial passivation of a zinc coating, when embedded in concrete, occurs within hours and is affected by the chemistry of the surface layer. The relationship between cement alkali content and zinc corrosion rate is important to understanding the initial passivation of galvanized coatings in concrete. The pH of cement in contact with the galvanized coating controls the formation of a compact and adherent layer of calcium hydroxyzincate (CHZ), a compound that passivates the surface of the zinc coating from further reaction with the concrete. The threshold for passivation of zinc in concrete pore solutions is at a pH of between 12.8 and 13.2 +/- 0.1. PH levels greater than 13.2 do not develop in concrete pore solutions during the first few hours if sulfate is used as a settling regulator, or enough alkaline sulfates are present. The passivation layer develops during the first few hours after mixing when the pH of the concrete solution is lower than 12.8 +/0.1. If pH is between 12.8 and 13.2, the layer develops slowly and the galvanized coating may continue to react until the passivating layer is formed. In any case, regardless of the pH level of the concrete, the presence of a pure zinc layer

STRUCTURE magazine

sustainability and preservation as they pertain to structural engineering

Zinc-Coated Reinforcing Steel

Improving Performance of Concrete Structures By Mike Stroia

Mike Stroia is the National Marketing Specialist of AZZ Metal Coatings, GalvaBar. Mike is an active member of CRSI, NACE, ASTM and AGA. Mike can be reached at mikestroia@azzgalv.com.

The online version of this article contains references. Please visit www.STRUCTUREmag.org.

CGR formability.

is key to the rapid formation of a compact passivating film of CHZ on the galvanized reinforcement. The corrosion of reinforcement occurs while in service when aggressive species (carbonation front or chloride ions) reach the reinforcement. These aggressive species have to disrupt the physical barrier of the CHZ film to initiate corrosion of galvanized reinforcement. Carbonation lowers pH from highly alkaline to around neutrality (pH 7), where the rate of Zn corrosion is very low. As a result, galvanized reinforcement does not generally corrode in carbonated concrete. Chlorides are the more aggressive ions for reinforced concrete and are the most frequent cause of reinforcement distress. Chloride ions come from the raw construction materials, marine environments, or deicing salts. Zinc is attacked by chloride ions but has a higher threshold value for corrosion to initiate than bare steel. That is, the concentration of chloride ions needed to start corrosion of zinc is up to four times higher than the concentration required to start corrosion of black steel. The overall behavior depends on the source of the chloride ions, the state of the galvanized surface (including protection afforded by Zn corrosion products), and the degree of protection provided by the concrete cover. The corrosion of steel in concrete can be viewed as developing through a two-stage mechanism: initiation and propagation. Efforts to achieve long-term durability of reinforced concrete have been mostly directed at delaying initiation of corrosion of the reinforcement, i.e. postponing as long as possible the start of the propagation stage. The presence of a pure zinc layer on the surface of the steel reinforcement is the best way to delay the onset of corrosion of the reinforcement. The tenacious passivating film of CHZ is the first line of defense. The pure zinc layer will then corrode uniformly at less than one-tenth the corrosion rate of the base steel, thereby extending the onset of corrosion of the steel reinforcement. It should also be noted that the zinc corrosion products migrate away from the corrosion site and help densify the concrete surrounding the reinforcement, further delaying the onset of corrosion and also increasing bond strength.

New York Bridge. Courtesy of the New York State Thruway Authority.

Recent research from the National Research Council of Canada reviewed how zinc-coated reinforcing steels perform favorably compared to uncoated reinforcing steels. In heavily chloride-contaminated concrete, galvanized steel was found to have 5-10 times lower corrosion rates than carbon steel, depending on environmental exposures. The NRC report, Condition Assessment and Corrosion Mitigation of Galvanized Steel Reinforcement in Concrete Structures, presents the corrosion performance of galvanized steel as compared to carbon steel. It also explores the corrosion mitigation strategies for further improving its corrosion resistance to extend the service life of concrete structures. The three-year study included a comprehensive program to obtain corrosion data that represent a broad spectrum of corrosion states of galvanized steel in concrete structures. The corrosion rates spanned over five orders of magnitude, from a passive state to low, moderate, and high corrosion rates, by combining the key corrosion parameters including environmental exposure and chloride content as well as concrete type. These data were used for both corrosion performance analysis and statistical analysis for the development of model/guidelines for corrosion condition assessment. It also included a field survey that was conducted on two highway bridges, and the collected half-cell potential data were used to validate the developed condition assessment model/guidelines. Another recent University of Waterloo thesis, Evaluation of the Corrosion Behaviour of Continuously Galvanized Rebar,

STRUCTURE magazine

April 2017

reviews autopsied concrete slabs that contained several varieties of black and galvanized reinforcement after 450 days of exposure. Electrochemical test measurements were made throughout the life of the project. For the corrosion potentials, ASTM C876 which characterizes black steel corrosion in concrete was referenced. These were taken biweekly over the 450-day period for three types of concrete samples: sound (non-cracked), transverse cracked, and longitudinally cracked samples. The electrochemical readings were interpreted using the NRC report which gave the threshold values for corrosion of zinc in concrete. Results demonstrate that zinc coated reinforcement performs better than conventional uncoated reinforcement in all cases. Zinc-coated reinforcing steels are an optimal way of preserving concrete assets with their proven performance, durability, and cost effectiveness. Hot-dip galvanized reinforcing steel is widely available throughout North America. Continuous Galvanized Reinforcement (CGR) will be available in North America in early 2017 and is currently available in Xiamen, China, and in Dubai, UAE.▪

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Structural SpecificationS updates and discussions on structural specifications

Residential Wood Deck Design By John “Buddy” Showalter, P.E. and Loren Ross, P.E.

ccording to recent industry reports, 6,500 people have been injured from collapsing balconies and decks in the United States since 2003. Complicating matters for existing homes, the North American Deck and Rail Association (NADRA) estimates there are 40 million decks in America that are more than 20 years old. This means these decks were installed prior to today’s building codes. To encourage compliant deck design and construction, the American Wood Council published Design for Code Acceptance No. 6 – Prescriptive Residential Wood Deck Construction Guide (DCA 6). The latest version reflects requirements in the International Code Council’s (ICC) 2012 International Residential Code (IRC) and other provisions pertaining to single-level residential wood deck construction. DCA 6 can be found at www.awc.org/codes-standards/publications/dca6. Engineers may be called upon to design decks or certain portions of them. They may also be involved in inspection and retrofit activities related to residential wood decks. The purpose of this article is to highlight certain engineering topics related to DCA 6 and provide some of the background for those issues. Much of the information is taken from the DCA 6 Commentary.

Minimum Requirements and Limitations John “Buddy” Showalter is Vice President of Technology Transfer for the American Wood Council and serves as a member of the STRUCTURE magazine Editorial Board. He may be reached at bshowalter@awc.org. Loren Ross is Manager of Engineering Research with the American Wood Council. He can be reached at lross@awc.org.

DCA 6 applies to single level residential wood decks only. Multi-level decks create additional variables such as concentrated loads due to stairs. Structural members and connections shown in DCA 6 have been sized based primarily on a uniformly distributed floor live load of 40 psf and a dead load of 10 psf (table footnotes specify where other point loads have been considered). If a deck is not prone to sliding or drifting snow, the criteria in DCA 6 can be conservatively applied to a deck with a uniformly distributed snow load of 40 psf and a 10 psf dead load. Concentrated loads such as those created by hot tubs are beyond the scope of DCA 6 and require a design professional or other approved installation approach. All decks prescribed in DCA 6 assume the primary structure resists lateral forces per Section R507.2.3 of the IRC.

Decking Requirements The online version of this article contains detailed references. Please visit www.STRUCTUREmag.org.

Alternate decking materials or alternate methods of fastening decking to joists can have a critical impact on the resistance of lateral loads. Equivalent strength and stiffness developed by alternative materials and fastening methods are necessary to ensure adequate lateral capacity. An example is a

16 April 2017

use of “hidden” fasteners for edge-grooved decking material. The potential problem with this type of fastener system is that the deck boards provide very little to no diaphragm capacity or stiffness for the deck with respect to lateral loads. As discussed in the Deck Lateral Loads section below, decking can provide diaphragm capacity and stiffness, but those strength and stiffness values assume face nailing of the decking into the framing.

Joists and Beams Joist span calculations assume a 40 psf live load, 10 psf dead load, L/360 deflection limit for simple spans, No. 2 grade lumber, and wet service conditions. Overhang (cantilevers) calculations assume L/180 cantilever deflection with a 220-pound point load (same as used for span rated decking), No. 2 grade lumber, and wet service conditions. Joist spans are limited to a maximum of 18 feet, with beams and footings sized accordingly. If longer joist spans are designed, joist hangers, beams, posts, and footings will have to be analyzed to ensure appropriate load path. Joist spans can cantilever past the beam, or the joists may attach to one side of the beam with joist hangers. Deck beam spans can extend past the post up to LB/4. Beams are sized based on tributary load from joists framing in from one side only within the span limits.

Deck Framing Plan For resistance of lateral loads, the deck is assumed to act as a diaphragm in an open-front structure. The decking, when nailed to the joists and rim joist, acts as sheathing in this diaphragm. Larger aspect ratios may be permitted where calculations show that larger diaphragm deflections can be tolerated.

Joist Hangers Research has shown that joist-hanger-to-ledger connections resist lateral loads. When permitted by the hanger manufacturer, the use of screws instead of nails to attach hangers to the ledger can decrease the potential for the joist to pull away from the ledger.

Post Requirements A minimum 6x6 nominal post is specified in DCA 6. IRC section R407.3 specifies a minimum 4x4 (nominal) wood column size; however, it would often be overstressed in applications covered in DCA 6. Further, this simplification provides adequate bearing for beams. Note that notching the post to accommodate a nominal 3x, 4x, or 2-ply 2x beam exceeds notching limits for bending members. Therefore, if posts are embedded and designed to resist lateral load conditions, the post would need to be designed per the National Design

Specification® (NDS®) for Wood Construction. An option of 8x8 nominal posts allows for a deck height of up to 14 feet in all cases. Prohibiting attachment of the beam to the sides of the post with fasteners only ensures wood-to-wood bearing. The design of fasteners for wet-service conditions requires significant capacity reductions and should be evaluated by a design professional. Diagonal bracing can contribute to the stiffness of the deck and, therefore, cause additional lateral loads on the posts. Since center posts receive more vertical load than corner posts, additional lateral load can cause overstress. For this reason, DCA 6 does not show the use of diagonal bracing on center posts. The lateral force applied to corner posts is based on the capacity of the connection at the brace. Therefore, the full capacity of the brace connection is assumed to be developed and applied 2 feet below the beam.

The requirement for minimum distance between the top of the ledger and the bottom row of fasteners is based on NDS 3.4.3.3(a) for shear design at connections. When the connection is less than five times the depth, 5d, of the bending member from its end, an adjusted design shear must be calculated. The connection of ledgers to existing empty or hollow masonry cell blocks is not practical. Most manufacturers of concrete block anchors do not publish allowable shear values for a ledger connected to empty hollow masonry block of unknown compression and breakout

strength. Due to the uncertainty and lack of test data for this application, use of a non-ledger deck is recommended for this application.

Non-Ledger Decks The provisions of DCA 6 assume that the primary structure is used for lateral stability. A non-ledger deck, as defined in DCA 6, is vertically independent of the primary structure but still relies on the primary structure to resist lateral loads, whereas a free-standing deck is both vertically and laterally independent. continued on next page

Footings

Ledger Attachment Requirements Fastener spacing requirements in DCA 6 are based on 2012 IRC R507.2.1, which is based on testing at Virginia Tech and Washington State University (Carradine et al., 2006). Designers should note that this empirical approach allows for greater fastener spacings than can be calculated per the NDS. It also permits the use of lag screws that don’t meet the minimum fastener penetration requirements into the main member for lag screws. The basis for edge distances and spacing between rows is NDS Tables 11.5.1C and 11.5.1D, respectively, for perpendicular-tograin conditions. Per NDS Table 11.5.1C, edge distance is 4D (where D is fastener diameter) for the loaded edge. Per NDS Table 11.5.1D, the spacing between rows is based on the l/d ratio of the fastener. Per 11.5.1.3 of the NDS, the maximum spacing between fasteners is 5 inches. This requirement is based on potential shrinkage of the ledger, which could create tension perpendicular-to-grain stresses if the outer edges of the ledger are constrained by bolts. STRUCTURE magazine

SEE FIBRWRAP.

April 2017

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Footing sizes are based on the assumptions of 1,500 psf soil bearing capacity and 2,500 psi compressive strength of concrete, which are the minimum values based on IRC Tables R401.4.1 and R402.2. A concrete weight of 150 pcf is also assumed, making solving for the footing size an iterative process.

Deck Lateral Loads The IRC currently does not state the design lateral loads for decks, but it does provide an approved design which DCA 6 incorporates. DCA 6 states that the document does not address lateral stability issues beyond those addressed in Section R507.2.3 of the IRC. IRC R507.1 requires anchorage of the deck to the primary structure to resist lateral loads. Further, the IRC includes hold-down tension devices as a prescriptive means to achieve compliance with the lateral load connection requirements without mandating engineering (see IRC Section R507.2.3). Instead of the prescriptive 1,500-pound hold-down tension device specified, an alternate engineered connection detail would be required. To ensure transfer of tension device loads into the floor diaphragm, DCA 6 shows nailing from above through floor sheathing and into floor joists or blocking between floor joists of the house. An equivalent connection from underneath is permissible using framing angles and short fasteners to penetrate into the floor sheathing. Decks are assumed to be similar to openfront structures defined in American Wood Council (AWC) Special Design Provisions for Wind and Seismic (SDPWS). Decks covered in DCA 6 are assumed to be diaphragms that cantilever from the house and are limited to a deck length-to-width ratio of 1:1. Larger aspect ratios may be permitted where calculations show that larger diaphragm deflections can be tolerated. Designers should also note that diagonal sheathing (deck boards at 45 degrees to the joists) provide a much stronger and stiffer diaphragm. A comparison of diagonal lumber sheathing versus horizontal sheathing (boards perpendicular to joists) in SDPWS Table 4.2D reveals a four-fold stiffness increase for diagonal sheathing. For non-ledger decks, DCA 6 prescribes three methods of transferring lateral loads from deck joists to the rim board: joist hangers, blocking, or use of framing angles. This connection is to transfer forces acting parallel to the house. A connection equal to the diaphragm capacity of single layer diagonal boards, or approximately 300 plf, is required. Diagonal (knee) bracing is commonly used on decks to help resist lateral forces and provide increased stiffness; however, the IRC does not prescribe diagonal bracing.

Guard Post Attachments for Required Guards Both the IRC and International Building Code (IBC) specify that guardrails and handrails be capable of resisting a minimum concentrated live load of 200 pounds applied in any

direction for required guardrails (see IRC R312.1). Commonly used residential guardrail post connections were laboratory tested at the required load level for a code-conforming assembly per the IBC (Loferski et al., 2006). A commercially available connector, typically used in shear wall construction, was tested in a post-to-deck residential guardrail assembly. The connection passed a load test based on code provisions for a “tested assembly.” Connection details in DCA 6 reflect these test results. A minimum requirement of 1,800 pounds for the hold-down connector ensures adequate capacity (Loferski et al., 2005) for a 36-inch maximum rail height. A higher rail height requires the design of a higher capacity connector. Manufacturers’ tabulated values for hold-down connectors typically include a load duration (CD) increase of 60% since connectors for shear walls are used to resist wind and seismic loads. The 200-pound concentrated load requirement for guardrails is assumed to be a 10-minute load duration (e.g. it would not see a maximum 200 pounds outward load for more than 10 minutes cumulatively in its lifetime). Therefore, CD=1.6 is used for hold-downs in this application. DCA 6 shows minimum and maximum spacing requirements for bolts in deck joists and deck rim boards. The 5-inch maximum spacing is per NDS 11.5.1.3. This requirement is based on potential shrinkage of the joist or rim board, which could create tension perpendicular to grain stresses if the outer edges of the deck joist or rim are constrained by bolts. To achieve the minimum spacing requirements, a nominal 2x8 or wider (deeper) outside joist or rim board is required.

Stair Requirements DCA 6 shows 5/4 boards spanning 18 inches or less. Specific products classified by size as decking are usually assigned a recommended span of 16 or 24 inches. Additionally, IRC Table R301.5 footnote (c) requires a 300pound concentrated load check on stair treads. Analysis revealed that 2x8 No. 2 Southern Pine works for a 34½-inch span (36 inches minus ¾-inch bearing at each end) when the 300 pounds is distributed across 2 inches (e.g. 150 pli), based on L/288 deflection criteria (ICC-ES Acceptance Criteria 174 requires 1/8-inch deflection limit: 36-inch/ 1/8-inch = 288). Solid stringers were analyzed as simple span beams using the horizontal span, not the actual stringer length. Cut stringers were analyzed with 5.1-inch depth which is based

STRUCTURE magazine

April 2017

on 7.75:10 rise-to-run ratio. A size factor, CF, of 1.0 is used since 2x12 is the size basis.

Stair Footing Requirements Stair stringers should be supported by bearing at the end where the stairway meets grade. The default footing assumes a 40 psf live load and 10 psf dead load over a tributary area of 18 inches and one-half of the maximum span of 13 feet–3 inches permitted for solid stringers. This calculates to 500 pounds. While bolts are sometimes used for this detail, proximity to the end of the stringer could lead to splitting of the stringer – especially cut stringers. The 2x4 bearing block alleviates this situation. However, in addition to the bearing block, bolts would also be required to provide lateral support if a guard post is used.

Framing at Chimney or Bay Window Where the header frames into the trimmer joist, a concentrated load is created. This condition was evaluated and the analysis revealed that the distance from the end of the trimmer joist to the point where the header frames into it – designated as dimension “a” – must be limited. Bending and shear were checked to determine the reduction in a double trimmer joist span when carrying a 6-foot header. Bolts or lag screws used to attach the trimmer hanger to the ledger are required to fully extend through the ledger into the band joist or rim board. If a typical face mounted hanger is installed where only nails are used to attach the hanger to the ledger, the ledger would carry a significant portion of the load. Since a concentrated load would be created on the ledger, it would be resisted by the bolts at the end of the ledger. The provisions for minimum distance, de, between the top of the ledger and the bottom row of fasteners is based on NDS 3.4.3.3(a) for shear design at connections.

Conclusion Engineers may be called upon to design residential decks or inspect existing decks. While prescriptive provisions for deck construction are readily available, an understanding of the basis for those provisions will help engineers with the design process.▪ This article is adapted from Wood Design Focus (Volume 26, Issue 3) and used with permission from the Forest Products Society.

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Structural rehabilitation renovation and restoration of existing structures

A bridge structure exposed to salt can expect corrosion of the embedded steel during its service life. Cathodic Protection (CP) has proven itself as the only permanent repair of existing corroded steel reinforced concrete. Therefore, CP must not be considered separately, but as a part of a complete rehabilitation program. (1993 Strategic Highways Research Program (SHRP) Report S-337)

athodic Protection (CP) is an electrochemical corrosion mitigation technique with origins dating back to 1824. Earlier though, in 1800, Alessandro Volta’s voltaic batteries were presented to the Royal Society, illustrating that electrical current was generated when metals with a different electro-potential were stacked together and separated with a cloth saturated in brine. It was Sir Humphrey Davy (Figure 1) who observed that the zinc electrode was corroded and the other electrodes, such as silver, gold, and copper, remained undamaged. Davy’s observations eventually led him to the concept of the electrochemical series of elements. In 1806, Davy promoted his findings showing that copper in sea water was protected from corrosion when in contact with iron or zinc. Davy was able to apply his concept of electrochemical protection when, in 1823, he was ordered by the British Navy to assist with copper sheathing failures on wooden boats. Davy led the investigation into the rapid corrosion of Royal Navy ships’ hulls in sea water. His electrochemical cathodic protection system was applied to the HMS Samarang, which showed signs of corrosion after only three years in use. The system consisted of attaching four cast iron anodes on the hull: two on the stem and two on the bow, with a surface ratio of 1:80 of the copper surface. The attachment of the iron plates to copper sheathed wooden boats became standard practice in the British Navy after that. Eventually, zinc was used to protect steel hulls.

Cathodic Protection of Infrastructure By Paul Noyce and Gina Crevello

Paul Noyce is a Material Science and Concrete Durability Expert for existing and new structures. He is Chairman of the National Association for Corrosion Engineers Standard Technical Group 01 for Reinforced Concrete and serves as Chief Technical Officer for Echem Consultants. He can be reached at pnoyce@e2chem.com. Gina Crevello is a Materials Conservator and Principal of Echem Consultants. She is a Board member of the Association of Preservation Technology. She can be reached at gcrevello@e2chem.com.

The online version of this article contains references. Please visit www.STRUCTUREmag.org.

The Evolution of Cathodic Protection These early systems, based on the galvanic series of metals, utilized a metal with a more negative electro-potential to protect the more noble metal. Galvanic systems rely on the electrolysis of the metal following the laws established by Sir Michael Faraday in 1833. The oxidation of the ‘galvanic’ or sacrificial anode provides electrons at the cathode site where the reduction reaction or gain of electrons occurs. This protects the more noble metal. Like a battery, system requirements include an anode, a cathode, an electrolyte, and a metallic path. There is always a direct circuit between the anode and the cathode. The anode will eventually require replacement upon decomposition. While often erroneously referred to as

20 April 2017

Figure 1. Sir Humphrey Davy.

ICCP System Components The major components of Impressed Current Systems include: • An external DC power source • Anodes for current distribution • Conductive electrolyte (concrete) • Protective steel • Wiring for circuit completion • Monitoring system Power supply units (PSUs) and main control unit (MCU) technology rapidly changes, as do means of communicating with systems. ‘passive’ systems today, galvanic cathodic protection (GCP) systems do not rely on an external power supply. Impressed Current Cathodic Protection Systems (ICCP), which depend on an external power source, have a younger history with late 19th century origins in the United Kingdom (UK). In referring to a corrosion problem of condensers in a power plant in 1919, Mr. M.J. Christie, of the Southwick Power Plant, chronicles the use of a Cumberland electrolytic system in the Journal of Electricity. He states that corrosion and the graphitization of the cast iron piping due to the use of sea water were the most far-reaching and significant concern for power users. He adds that his corrosion problems at the Southwick Power Plant were positively resolved when an electrolytic system was installed in the condensing systems. From the 1920s forward, the use of ICCP was employed in buried structures such as pipelines, tank bottoms, and windmill foundations. By the

Figure 2. Left: Installation of an ICCP System on a pedestrian bridge. Probe MMO Ti anodes are installed on the parapet and slotted MMO Ti anode ribbon on the deck slab. Right: Pedestrian bridge after installation.

1950s, it was standard practice to use ICCP for the protection of any subgrade service carrying hazardous materials and cathodic protection was accepted as a means of corrosion mitigation. The earliest introduction of ICCP to protect reinforced concrete structures was in 1955 when it was used on concrete pipes. The National Association of Corrosion Engineers was established in the United States in 1953. Cathodic Protection became an important means of preserving infrastructure, in large part because of the efforts of this organization to promote CP use.

Use of Cathodic Protection in Concrete Infrastructure In 1959, the use of ICCP was demonstrated in concrete with the use of silicon iron anodes in reinforced concrete bridge decks. By the 1970s, full systems were installed in reinforced concrete. It was around this time when it was realized that concrete is an ionic conductor and can support a small amount of electrical current flow. The historical use of ICCP and its early development within bridge systems between the 1970s and the 1990s is well documented by the 1993 SHRP S-337 Report: Cathodic Protection of Reinforced Concrete Bridge Elements: A State of the Art Report. The Report noted: “This theory was first put into practice by R. F. Strafull and co-workers in the California Department of Transportation on the Sly Park Road Bridge in June 1973… The first bridge deck CP system installed by the California Department of Transportation (Caltrans) covered only a portion of the deck. After several years, the protected deck section was compared to the unprotected portion,

and it was conclusively shown that the CP system prevented new delaminations from forming (except in epoxy-injected areas) and that the unprotected deck continued to deteriorate.” Similar studies were being performed in Canada and Europe with equal success. The SHRP Report also cites a 1988-89 survey conducted by Battelle, the world’s largest independent, non-profit research and development organization, indicating that more than 275 bridge structures in the United States and Canada were currently cathodically protected. At that time, “the total concrete surface under cathodic protection was almost nine million square feet (840,000 square meters)…Most of the bridges were 20 to 35 years old when cathodic protection was applied. Ninety percent of the protected structures [were] located in deicing salt regions and 10 percent [were] in marine environments.” ICCP and other corrosion mitigation strategies are often addressed when looking at critical structures which cannot be taken out of use, and when the cost and indirect impacts of replacing a structure greatly affect the owner, users, and local community. The 1990s and 2000s saw a proliferation of systems installed in Europe. The M4 motorway and Midland Links Projects in the UK were exploratory, essentially field programs that resulted in some of the largest ICCP system installations to date. The concluding remarks of the SHRP report state that “a bridge structure exposed to salt can expect corrosion of the embedded steel during its service life. CP has proven itself as the only permanent repair of existing corroded steel reinforced concrete. Therefore, CP must not be considered separately, but as a part of a complete rehabilitation program.”

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April 2017

Impressed Current Cathodic Protection (ICCP) systems with Mixed Metal Oxide (MMO) sintered titanium anodes can have a design life of more than 50 years. “MMO anodes are a composite structure with valve metal substrate (titanium) covered by an electrocatalytic film of noble metal oxide. The anodes are characterized by very little dissolution of the metal oxide and uniform wear rates” (Kroon, et.al. 2007). The life of galvanic CP systems is finite, based upon metal consumption of the anode. Where embedded, galvanic systems still require replacement when consumed. Today, impressed current cathodic protection is commonly used on all reinforced concrete structure types (Figure 2), though the decision-making process for the correct system choice often needs to have a rationale and service life established by the design team.

Decision Making Process for the Use of ICCP Impressed Current Cathodic Protection Systems provide a significant service life extension for reinforced concrete structures. When choosing the correct system, the owner’s service life extension expectations must be established, as well as where the structure is within its lifecycle. To make the appropriate choice, the structure, and performance expectations, the designer must be aware of various conditions. Construction details, construction materials, contamination levels, anode output, steel protective current requirements, system operations, and distribution logistics are all required to ensure an appropriate design. Therefore, before designing a system, an in-depth analysis of the structure should be carried out and analyzed by a qualified team with experience in corrosion and material durability issues. After determining the conditions which are driving corrosion and understanding the remaining service life, the investigator/ designer should provide the owner with a system matrix based on the structure’s and owner’s requirements. This matrix should cover system types available for the structure, operational and maintenance requirements, and monitoring requirements. It needs to be established from the onset that ICCP Systems are not fit-and-forget system types. The success of a system after installation is based on on-going monitoring by a qualified professional. A life cycle cost for the system types, compared to traditional repairs, easily illustrates the value of higher one-time costs expended now to mitigate corrosion. This comparison highlights long-term protection versus future ongoing patching programs and

Table 1. Repair options.

Number

Option

Do nothing

Analyze structural integrity

Reduce further deterioration

Improve/refurbish all or part

Reconstruct all or part

Demolish and build new

continued corrosion which will eventually lead to the loss of structural integrity. An example of a repair matrix is shown in Table 1. As part of the further analysis of the appropriate system for any structure, the selection choice and rationale for repair can be further assessed by establishing owner requirements (Table 2). Once requirements, desired service life, and work scope are established, corrosion control systems which fit the structure can be assessed. “Without a condition evaluation, and established rationale, the selection process for repairs [and corrosion mitigation] is difficult to achieve.” An example of the parameters established from a repair planning exercise for critical structures can be seen in Table 3. (See also Figure 3)

System Types Available for Infrastructure Projects Many anodes can be found on the market today, and some suppliers sell ‘systems.’ While there may be merit in compatible systems, the best practice is to perform an evaluation of the structure so that structure-specific systems can be designed. It is important that the correct material is selected for the long-term performance of a system (Table 4, page 24 ). Upon selection of the optimal anode type, the system designer can commence with the design. All CP systems, irrespective of system type (i.e. GCP or ICCP) or anode material (Zn or MMO Ti), and anode type (coating, probe, mesh), should always be designed by qualified professionals who

Figure 3. Installation of an ICCP System on a hyperbolic cooling tower with MMO Ti Ribbon.

are not suppliers of material. Often, a material interest by a supplier influences design selection where other system types may provide a more optimal performance. Impressed current systems are the only systems which will provide long-term performance and also electrochemically alter the conditions surrounding the steel.

Case Studies Many structure types are protected with ICCP, from transportation structures to critical infrastructure. The following case studies focus on a variety of structure types with longserving systems in place. Clyde Tunnel One of the longest operating Cathodic Protection systems in service is the Impressed Current Cathodic Protection system installed in the Clyde Tunnel under the River Clyde in Glasgow, Scotland. The tunnel is 2460 feet (750 meters) long with 30-foot (9-meter) diameter twin bore tunnel tubes, each containing an elevated reinforced concrete deck roadway. Ongoing degradation and aggressive corrosion was impacting the embedded steel of the reinforced concrete deck It was determined that the corrosion was accelerating as the road deck became contaminated by chlorides due to de-icing salts. There had been two previous repair contracts within the tunnel structure and both repairs

Table 2. Selection rationale.

Number

had premature failures. The engineering and contracting team indicated that it would be prohibitively costly to remove and replace all the contaminated concrete using conventional methods. Investigations indicated that corrosion had occurred in the top-level reinforcing steel of the road deck, as well as the more visible soffit-level corrosion from under the roadway. Before the final design, electrochemical repair techniques of chloride extraction (ECE) and ICCP were considered to minimize the extent of concrete removal. In 1994, a trial contract for CP was chosen over ECE to establish the effectiveness of ICCP using different types of anode systems and to assess how well they could protect the upper reinforcing steel. The resulting CP specification stated requirements for a design-and-construct ICCP system with a 25-year operating life. The work was completed in the West Tunnel before beginning in the East Tunnel. The installation program took two years to complete. The design focused on protecting the concrete surrounding the 187 joints. For the length of the tunnel, approximately 4 feet (1.2 meters) of concrete and steel were protected on either side of the joints. The system involved the use of MMO Ti mesh and anode ribbons with a concrete overlay, with each joint acting as an independent zone. This system was the first distributed ICCP system installed in the UK. In their 2015 Status and Options Report, the Glasgow City Council recommended the current ICCP system be upgraded as part of the continued on page 24

Table 3. Example of client repair rational.

Strategy

Selection Rationale

Intended use, design life, and service life

Performance characteristics requirements

Long-term performance of protection or repair

Opportunities for additional protection or monitoring

Acceptable number of repair cycles/cost

Future maintenance and access costs

Structures’ appearance STRUCTURE magazine

Reduce further deterioration and improve the longevity of the structures

Principle Address long-term performance of the structures based on age, location, exposures, use, current condition Method

Analyze structural integrity, carry out full depth concrete repairs and install an impressed current cathodic protection system (ICCP) for the reinforced concrete shell and a galvanic cathodic protection (GCP) for column legs

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Table 4. ICCP anode types.

Anode Type

Type

Surface Applied Conductive Coatings

Carbon Based

Surface Applied Metallized Zinc

Pure Zinc

15 years

Surface Applied Metallized Alloy

Zinc Aluminum Indium

15 Years

Expanded Zinc Mesh with Concrete Overlay

Zinc

15 Years

Expanded Titanium Mesh with Concrete Overlay

Mixed Metal Oxide Sintered Titanium

30 Years

Titanium Ribbons in Slots

Mixed Metal Oxide Sintered Titanium

40+ Years

Mixed Metal Oxide Titanium

40+ Years

Ceramic

30+ Years

Discrete Anodes in Conductive Grout (Probes) Clyde Tunnel Assessment Renewal Program. This was identified as a high priority, to be installed within 1 to 3 years as the power supply system is nearing the end of its service life. At present, the Renewal Program does not list concrete repairs associated with corrosion of embedded reinforcing steel of the road deck because the ICCP system has mitigated any further damage since it was installed. The Midland Links Motorway Viaducts (MLMV), which includes approximately 13 miles (21 kilometers) of elevated roadways, were the first reinforced concrete bridge structures in the UK to have electrochemical corrosion remediation systems installed. Across the entire MLMV, there are over 1300 spans, crossbeams, and expansion joints, and more than 3600 columns. Over the years, however, the MLMV system has suffered from structural deterioration, primarily corrosion of the reinforcement owing to chloride attack.

Impressed Current Cathodic Protection systems were installed in more than 740 of the bridge structures in the Midland Links to mitigate corrosion. This work was pivotal in developing and refining ICCP systems for bridge structures. Based on these studies, ICCP is now commonly used worldwide for corrosion prevention and mitigation in bridge structures.

While these two case studies are based on UK systems which were installed in the early 1990s, they are used to illustrate the longevity and durability of the concrete repairs which include the use of ICCP for corrosion mitigation. It has been documented both by CONREPNET (the Concrete Repair Network overseen by the British Research Establishment) and the United States Army Corp of Engineers that concrete repairs typically have less than a 50% satisfactory performance rating. The following statistics are often used:

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Corrosion Mechanisms

10 to 15 Years

Summary

Midland Links

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Service Life

April 2017

Carbonation/ Chlorides

5 years – 80% of repairs are satisfactory 10 years – 30% of repairs are satisfactory 25 years – 10% of repairs are satisfactory Cathodic protection was wholly successful in 60% of the installations reviewed; 20% required minor attention (80% functional) and 20% were nonfunctional. The review of the CP systems illustrated that there were minor faults in electrical mechanisms that lead to system malfunctions. All of these issues were easily rectified. With ICCP system designs, electrical components require 20-year replacement plans. Overall, the consensus of both programs was that properly installed concrete repairs, in conjunction with the installation of an Impressed Current Cathodic Protection System, provided the most durable and longest performing repair available. More recently, the increased use of system energy plants for critical infrastructures, such as intake structures and cooling towers, illustrates their large scale use of ICCP systems. These projects not only provided cost savings; return-on-investment (ROI) studies illustrated that the impact to the local economy and owners would be in the range of 1.4 Billion USD and the cost of comprehensive repairs that included an ICCP component would equate to $80 Million USD. The owner opted for repair with ICCP in each of these instances. With the staggering percentage of ailing infrastructure in the United States and the knowledge that corrosion grows exponentially, ICCP needs further consideration as a comprehensive mitigation tool to protect critical structures. The use of ICCP is well established in bridge and tunnel infrastructure, and should always be considered when owner expectations include extending service life, reducing future repair cycles, and minimizing life-cycle costs. Additionally, the use of ICCP as a sustainable and green system can be achieved by using solar powered systems.▪

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Structural SyStemS discussion and advances related to structural and component systems

or centuries, bridges and other structures were big, bulky, visually disruptive hulks. Stone, iron, and concrete made them symbols of strength and stability. Solid construction helped people feel more confident about crossing or entering them. Over time, they became lighter and more transparent. Innovative designs leveraging glass, plastic, cable, and sometimes environmentally-friendly recycled refuse replaced more solid materials to create bridges and buildings that are light, airy, beautiful – and stronger than their predecessors. What led to these enhancements? The fact that beauty lies in the eye of the beholder. Designers and engineers are never satisfied with what they see and are always imagining the future. Let’s look at some notable historic bridges that took the industry to the next level, and a few of the exciting designs currently on drawing boards that could propel it into the future.

Bridges with Brawn

How Beauty Beat Brawn Taking the BridgeBuilding Prize By Jeremy Herauf

Back when bridge construction was a novel concept, builders understood few basic engineering concepts. They knew that the load placed on the surface of a bridge had to be distributed to support structures. To compensate for the lack of more sophisticated scientific or engineering knowledge, designers naturally turned to bulk to enhance the strength of their structures. Over time, simple plank bridges, even hefty ones, proved to be ineffective, especially over vast expanses. Arch bridges were far more durable. The first ones were dense and heavy. Eventually,

Jeremy Herauf is the President of Bridge Masters, Inc., a company with over 40 years of experience installing and repairing bridge utilities. He has 20+ years of experience as a machinist, mechanic, and supervisor in the manufacturing industry, and served eight years in the United States Army. He can be reached at info@bridgemastersinc.com.

Pons Fabricius Bridge, Rome. Built in 62 B.C.

26 April 2017

builders found ways to make them lighter, more attractive, and better integrated into their environments. Three of the oldest arch bridges in existence illustrate this progression. Although it cannot be officially dated, the Arkadiko Bridge, located on the Peloponnesus in Greece, is believed to be the oldest arch bridge still in use. Dating from the Greek Bronze Age (32001050 B.C.), its heavy-duty design is a testament to its age and the primary reason for its longevity. The Caravan Bridge is the world’s oldest reliably dated bridge, going all the way back to 850 B.C. It is a stone arch span over the Meles River in Izmir, Turkey. Clearly, bridge designers had made strides to improve functionality, design, and environmental integration. The Pons Fabricius has connected Tiber Island to the heart of Rome since 62 B.C., the oldest bridge in the ancient city. It includes two broad arches, supported by a central pillar featuring a smaller arch built of ancient volcanic rock with brick and marble facing. Almost 800 years of bridge-building experience enhanced its beauty and effectiveness. Despite the strength and stability of these solid arch structures, they had limits. As cities grew and became more congested, newer bridges were needed that could function in densely-populated, interconnected urban environments.

Early Innovators As a next step, bridge builders turned to the emerging worlds of science and technology to find innovations to lighten, lengthen, and increase the strength of the bridges they built. Thought leaders like Leonardo da Vinci came up with

Brooklyn Bridge, New York. Opened in 1883.

Moses Bridge, Halsteren, The Netherlands. Built in 2010. (By Digital Eye [Own work] CC BY-SA 4.0, via Wikimedia Commons)

designs that imagined what a bridge could be in fresh new ways. However, like many scientific experiments, some failed during, or shortly after, construction. The Brooklyn Bridge was destined to be an engineering and design marvel from the day ground was broken in 1869. It is one of the oldest combined cable-stay suspension bridges, having survived more than 130 years under grueling vehicular, pedestrian, and train traffic. The cutting-edge design and new construction methods led to many injuries and deaths from decompression sickness (“the bends”) and other causes. The key reason the bridge has survived when so many similar ones failed is that it was built to be four to six times stronger than it needed to be. The Honeymoon Bridge crossed the Niagara River, connecting Niagara Falls, New York, to Niagara Falls, Ontario, from when it was completed in 1898 until 1938. It was an upper steel arch bridge that was considered stable, despite threats from its unique location and ice that formed in the winter. A great windstorm during the winter of 1938 pushed a record amount of ice against the abutments, causing the bridge to collapse. The original Tacoma Narrows Bridge was a grand engineering experiment and renowned bridge failure. At the time of its construction in 1940, it was one of the longest and slenderest suspension bridges in the world. It crossed a challenging section of Puget Sound in Washington State. Winds in the sound caused the bridge to vibrate, even during construction, and the structure collapsed less than six months after it opened. The bridge is still referenced in textbooks as an example of why it is critical to avoid aeroelastic flutter.

The Present Most people view today’s modern bridges as visual masterworks. They are stunning to look

at and enhance the everyday travel experience. However, underlying these beautiful structures are amazing engineering enhancements that make them stronger and safer than those built in earlier eras. The Chords Bridge has completely transformed the skyline in Jerusalem. This almost invisible, crystal-like structure was modeled on the concept of David’s lyre. It is a major rapid transit link that carries trains and pedestrians in a glass-sided structure. An innovative side-spar cable-stayed design allows the bridge to flow in a graceful curve, keeping it visually light, yet incredibly strong and stable. Who says a bridge has to be in the air or even be visible? The Moses Bridge in The Netherlands carries pedestrians across a canal under the water line in a trench that is virtually invisible at certain angles. It leveraged design and construction techniques similar to those used in dams to hold the water back. The name of the bridge refers to the biblical story of Moses parting the water. Everything that makes the design of the Kurilpa Bridge in Australia so light and attractive also makes it robust and stable. It is a multiple-mast, cable-stay structure based on advanced principles of tensegrity. This produces a solid synergy between balanced tension and compression components. The dazzling light show that makes the bridge so stunning at night is powered by a solar grid that contributes excess power to the city of Brisbane.

The Futurists What do bridge designers envision for the future? Much like the rest of the art and design world, they are creating structures that break all the rules – or combine them in new and innovative ways. This could lead to structures that are lighter, more beautiful and stronger than ever. In today’s

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April 2017

environmentally-sensitive world, many are turning trash into structural treasures. The basic plank bridge could get new life with new technology. It could be resurrected in the planned Econtainer Bridge that will connect Route 461 to Ariel Sharon Park in Israel. The park brings harmony to the urban landscape and nature, so this sustainable design made of used shipping containers is perfect for the site. The design even includes photovoltaic solar cells that will light the bridge and surrounding area at night, combining the most ancient of bridge structures with the latest environmentallyfriendly concepts. The Art Bridge is planned as a connector across the Los Angeles River, as well as a commentary on this famous body of water. Another plank design, the bridge will mostly be built from reinforced river trash, including bottle glass, cans, recycled tires, scrap metal, and more. Bridge lighting will be done in a completely environmentally friendly way. The brutal design is a reflection on the history and current state of the river, which has been significantly altered from its natural state. This concept for a new London Bridge takes bridge design to a higher level. Not only will people cross it, but they can also live, farm, and shop on it as well. The bridge becomes a completely environmentally friendly, selfcontained universe. The complex, integrated, lighter-than-air concept will help ensure the survival of the structure should something unexpected happen. The lesson to learn from all this? Bridge designers and engineers can never stop looking for new and innovative ways to build beautiful, strong structures. Technology has made it possible to build bridges that are lighter, stronger, and more sensitive to their environments. Beauty has always triumphed over brawn.▪

ALBINAYARD North Portland CLT Office Building By Blake Patsy, P.E., S.E.

lbina Yard, the first building in the U.S. to use domestically produced cross-laminated timber (CLT) panels as the primary structural building element, has recently wrapped up construction in North Portland’s Boise-Eliot district. The project is a 4-story, 16,000 square foot creative office building designed to accommodate small businesses looking to work in an environment with natural light and exposed wood. Providing an energy efficient workspace, and its shared conference rooms and courtyard, Albina Yard will be at home in the environmentally-conscious and communityoriented Mississippi Avenue neighborhood. The primary feature of the project is its exposed mass timber structural frame consisting of glue-laminated (glulam) beams and columns, and CLT floor/roof panels. Great care was taken in the design of the timber-to-timber connections to create a clean and modern timber aesthetic.

Significance Albina Yard is unique because the structure is almost entirely composed of mass timber elements, involving the early implementation of CLT, and also unique in its local “forest to frame” story. The story is framed by the sourcing, manufacturing, and fabrication of the timber components in the Northwest, along with the local development and design team: Reworks, Lever Architecture, and KPFF Consulting Engineers. At the forefront of the implementation of mass timber buildings in the U.S., the design team faced a number of atypical challenges and is paving the way for future mass timber projects to come. These challenges included addressing regulatory hurdles and seismic requirements (as it relates to the CLT diaphragm use) for the utilization of a relatively new product like CLT. Challenges also included understanding the currently limited CLT supply chain and fabrication capabilities in the U.S., navigating pricing challenges, and convincing risk adverse sub-contractors to price the job fairly. Aaron Blake, owner of Reworks and Albina Yard, LLC speaks to the many benefits of working with CLT: “We see Albina Yard as a catalytic project, paving the way for broad market adoption of mass timber construction in Portland and throughout the country. Mass timber products derived from sustainably managed forests allow us to build faster, stronger and less expensively with fewer environmental costs. Albina Yard is a proving ground for this new building technology, giving design teams and construction crews an opportunity to gain expertise that can be applied to much larger projects.”

Sourcing & Fabrication The goal from the outset of the project was to incorporate locallysourced timber products into the building. In particular, this included CLT panels manufactured by D.R. Johnson Lumber Co. out of Riddle, Oregon. CLT is manufactured by layering 2x members stacked STRUCTURE magazine

Exterior.

crosswise (at 90 degrees). Each layer is glued together to form panels up to 10 feet wide by 40 feet long. The perpendicular stacking creates a very strong, dimensionally stable product with two-way spanning capabilities. These properties and the large panel sizes create a distinct advantage over other timber flooring products considered. Thomas Robinson, the founder of LEVER and architect of Albina Yard and another CLT project, Framework, is a strong proponent of CLT and describes a few of the benefits: “The building design reveals the material qualities that are inherent to these new and innovative mass timber technologies. Because of the strength of the CLT panels, we can span longer distances with fewer beams and employ large, angled cantilevers that give the building façade a dynamic presence.” When the project started, D.R. Johnson was still in the process of completing the testing to receive ANSI/APA certification of their CLT panels, the first such certification for domestically produced panels. Anticipating approvals would be received, the design team created a framing layout customized to the panel sizes capable of being produced, which was a maximum of 10 x 24 feet at the time. This included forging a relationship between D.R. Johnson, who also supplied the glulam beams and columns, and Cut My Timber from Portland, Oregon, one of the few outfits with computer-numericcontrolled (CNC) machinery capabilities in the Northwest.

April 2017

Scan to see a video of the construction.

Interior.

The Frame The gravity structure for the project includes gypcrete-topped CLT floor panels supported by a glulam post-and-beam structure, with custom concealed timber-to-timber connections. The design of these connections required meaningful collaboration among Lever Architecture, KPFF Engineers, and Cut My Timber to determine realistic tolerance expectations and understand CNC capabilities. Ideally, all of the connections would have been fitted up in the shop to ensure a smooth installation on site. Unfortunately, due to schedule constraints, this was not possible for the first delivery of glulam members. The team discovered first hand that the timber could be fabricated to much tighter tolerances than the steel connectors themselves. Simple variations in weld sizes thus required field modifications to timber members receiving the steel connectors on the first level. The fabrication of subsequent glulam shipments was modified to allow for greater variations in the welds, resulting in a smoother installation process. The prevalence of concealed connections is only going to grow with the increased adoption of CLT. This will include the use of mass timber in fire rated construction where wood cover at the connections will serve to protect the concealed steel connectors. Thus, the ability to coordinate the connection design with the end fabricator will become ever more important.

During the design process, the State of Oregon came out with Statewide Alternate Method, No. 15-01 Cross-Laminated Timber Provisions, which brought forward the CLT provisions in the 2015 IBC and included conservative seismic design parameters for CLT as seismic force-resisting elements (Response Modification Factor, R=2). Working with the Statewide Alternate Method, and in close collaboration with the State of Oregon Building Codes Divisions, the excess plywood sheathing layer was removed to allow the CLT to act alone as the horizontal diaphragm. The diaphragm connections, CLT spline connections, and CLT-to-drag connections were designed to remain essentially elastic. The design team decided to continue with plywood-sheathed shear walls, rather than switch to CLT shear walls, due to the added ductility and associated higher Response Modification Factor this system provides (R=7). Outside the State of Oregon, CLT can still be used as a lateral force-resisting element through the Alternate Material and Method provisions in the code which allows a performance-based design of these elements. This will require additional research and analysis on the Structural Engineer of Record’s part, and the path to approval should be coordinated with the Authority Having Jurisdictions from the outset of design. continued on next page

Seismic Portland is in a seismically active region and, as a result, Albina Yard is required by code to meet specific seismic performance objectives. Even with the adoption of the 2015 International Building Code (IBC), which recognizes CLT as a material for the first time, there is still no direct code guidance on how to adapt CLT for use as a shear wall element or horizontal diaphragm. As a result, the design team initially sought to use CLT as a gravity support member only to avoid potential schedule delays associated with a performance-based design. Originally, the vertical lateral force resisting system was to consist of light framed plywood shear walls and the CLT floor panels were to be topped with a plywood sheathing layer to create a horizontal diaphragm conforming to existing seismic provisions. CLT stair.

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April 2017

CLT concealed beam/column assembly.

Construction.

Construction There are major advantages to the use of CLT in mass timber construction, such as reduced construction schedules and reduced manpower required. However, it does require significantly more pre-construction coordination and planning on the A/E/C team’s part, in comparison to a typical project. On the design team side, this includes working with the manufacturer to develop an efficient panel layout and coordinating all MEP penetrations in advance of fabrication to limit field cutting of the panels. An accurate 3D Building Information Model (BIM) is essential to this process to avoid potential conflicts and can prove helpful to the manufacturer for pricing and development of shop drawings. Understanding and coordinating acceptable tolerances between trades is also crucial. With the aid of CNC machinery, the tolerance capabilities of the timber components can be equivalent to concrete or steel construction. As a result, any additional tolerances which can be built into the design, particularly at the interface of different materials, can help ensure a successful project. For efficient installation, the contractor will want to pre-plan everything down to the order the panels come off the truck to speed up erection. If planned correctly, the installation can go extremely quickly. For Albina Yard, Timberland Framing Contractors installed the first level of CLT, approximately 4,000 square feet, in 4 hours. By the time they reached the 4th level, they had completed installation at this level in 2 hours with a crew of 5.

construction. Notably, another collaboration with this team is The Framework Project, a proposed 12-story mixed use, mass timber building in Portland, Oregon, which was named the West Coast Winner of the USDA-sponsored U.S. Tall Wood Building Prize Competition (https://tallwoodbuildingcompetition.org). Valerie Johnson, President of D.R. Johnson Lumber, reminds us of additional benefits. “Tall wood buildings have a great environmental story, and advanced wood products make better use of our state’s greatest natural resource. Increased use of these products in taller wood buildings means more jobs for rural communities that have been experiencing an economic decline for years.”▪

Future The demand for mass timber construction, specifically the use of CLT, is on the rise and is only expected to grow once the schedule benefits and associated cost savings are fully realized for development and STRUCTURE magazine

Blake Patsy, P.E., S.E., is currently the Managing Principal for KPFF’s Portland structural office. Due to his expertise in seismic design and his familiarity with Portland, Blake serves on the Structural Advisory Board for the City. Blake can be reached at blake.patsy@kpff.com. All graphics courtesy of LEVER Architecture.

Project Team Project Owner: Albina Yard LLC Structural Engineer: KPFF Consulting Engineers Developer/General Contractor: Reworks Architect of Record: LEVER Architecture Glulam/CLT supplier: D.R. Johnson Lumber Co. CNC Machining: Cut My Timber Lighting Designer: O-LLC Project Support: Woodworks April 2017

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ECONOMICAL LONG-SPAN HIGH-RISE By Cary Kopczynski, P.E., S.E., FACI and Joe Ferzli, P.E., S.E.

iktoria Tower, at the heart of downtown Seattle, fosters urban living with 249 upscale apartment units ranging from studio to 2 bedrooms, six levels of parking above grade for tenants, and 3,700 square feet of street-level retail which spurs community revitalization. The project is LEED certified and incorporates an assortment of eco-friendly materials, which utilize sustainable building practices. Viktoria is a 25-story upscale apartment tower with no internal columns, creating an open floor plan that offers spacious layouts with maximized usable square footage. Originally conceived as a condominium tower, the project was reinvented midstream to accommodate swelling demand for apartments from young urban renters. One of Viktoria’s most prominent features is its expansive floor plans. The structure has no restricting inner columns from the core to the exterior glass line, providing completely open interior space, architectural flexibility, and enhanced views from each unit. Viktoria’s socially-focused amenities include a rooftop terrace with outdoor BBQ stations, party room, indoor sky lounge, theater room, and a fitness center. With dazzling 360-degree panoramic views, the entire 25th floor is devoted to a resident lounge. Featuring an evergreen tree which pierces through an oculus opening, a dramatic butterfly roof, which cantilevers more than 20 feet from the enclosed portion of the sky lounge, adds a unique charm to the modern high-rise building. Viktoria Tower, Seattle.

State of the Art Structural Design Cary Kopczynski & Company (CKC) is the structural engineer of Viktoria. The structural system consists of cast-in-place concrete with post-tensioned floor slabs and a shear wall core for seismic and wind resistance. Using high strength concrete in the lower level core walls, the column sizes and concrete volume were effectively decreased. The architectural revisions associated with the conversion from condominiums to apartments impacted the entire design team. Additionally, the upgrade from the 2003 International Building Code (IBC) to the 2009 IBC particularly affected the design of shear walls. Substantial cost savings were achieved by modifying the core design, relocating subterranean parking above grade, and incorporating several value-engineering modifications to the structure. In retooling the building, the unit count was increased and the average unit size decreased. With a tight building footprint, the engineer was compelled to find a creative solution to attain the owner’s vision of large, open floor plans with minimal structural obstructions. After a number of structural frame iterations, CKC proposed an innovative solution to eliminate all internal columns. Slab spans of nearly 40 feet from the central core to the exterior glass line were made possible by increasing slab thickness around the perimeter of the core. This provided completely open living units and parking layout without structural obstructions. The long span floor system was carefully analyzed using a hybrid post-tensioned concrete where precompression forces and tendon profiles were designed to balance gravity loads. STRUCTURE magazine

Drophead floor plan.

April 2017

Column free space.

Core wall vertical reinforcement ratio demand.

Due to proximity to adjacent buildings, the loads were minimized at the building perimeter to avoid settlement effects. The engineer also minimized sideway motion during an earthquake to eliminate the possibility of contact with the surrounding buildings. State-of-the-art finite element and analysis tools were used to predict building drift and diaphragm deflection limits. During construction, the contractor discovered that the foundation of the adjacent building was crossing over the property line. The foundation of Viktoria was therefore carefully adjusted to bridge over the existing foundation. Close communication and synergistic coordination between the design and construction teams empowered CKC to make a rapid design change while keeping the tight construction schedule on track.

The drophead eliminated transfer beams, which would have been otherwise required to shift, or “transfer” the location of interior columns as they pass through the lower retail, lobby, and parking levels. The Viktoria tower obstruction-free layout also streamlined the installation of non-structural interior walls, eliminating the need to build around restrictive columns. The strategic incorporation of post-tensioning allowed the use of 8½-inch slabs despite the ultra-long spans. This minimized structural mass, and consequently seismic forces, which benefitted the columns, core walls, and foundations. Additionally, high-strength concrete in the lower level core walls effectively decreased the column sizes and total concrete volume. With close communication in the early design process, this innovative core design created positive outcomes for all involved in the design of Viktoria. The owner gained additional leasing space, the design team benefited from increased architectural flexibility and improved structural efficiency, and the contractor was able to expedite the construction process. Despite several engineering challenges, CKC’s creative solution helped the design team achieve the owner’s vision for the project. The result was a state-of-the-art modern residential tower with no internal structural obstructions.

Design and Structural Benefits of Drophead With urban real estate at a premium, maximizing usable interior space and view from each unit is critical. Creating open layouts in concrete towers with flat plate slabs is difficult due to the need for internal columns to keep slab spans within reasonable ranges. The Viktoria design team developed an innovative shear wall core design which provided a way to eliminate all interior columns, increase architectural flexibility, and improve structural efficiency. A column-free space was achieved by thickening the slab layout from 8½ inches to 16 inches for a distance of six feet at the corridor around the core perimeter. This stiffened the slab and created a unique core “drophead” system that eliminated the need for internal columns. Spans were increased to nearly forty feet, creating a column-free space throughout.

Team Collaboration Viktoria is an excellent example of successful teamwork. The owner, architect, engineer, and contractor worked closely from the early design phase to create a one-of-a-kind building that not only compliments the architectural intent but also meets the reality of the business world. continued on page 34

Lateral system.

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April 2017

Weber Thompson is the architect responsible for Viktoria’s architectural design, interior design, and landscape architecture. Viktoria is designed for those who want to enjoy downtown living without the commitment of purchasing. To that end, the architect integrated upscale yet approachable design elements with a neutral and elegant Northwest palette throughout. Its slender architecture is streamlined with vivid vertical metal panels and layers of glass curtain wall. Its strong verticality is accentuated with precast concrete, which creates a sense of symmetry and balance to the design. All private decks were transformed to bay windows to capture additional leasing area, to create spectacular views right off the units’ dining rooms, and to foster active social amenities. Turner Construction was the general contractor responsible for the overall coordination and day-to-day oversight of the project. Safety was of utmost importance to Viktoria’s construction team. Turner implemented numerous safety protocols, such as subcontractor screening, daily foreman meeting, and ladder policy. Close communication between Turner Construction, Weber Thompson, and CKC was the key to the successful implementation of Viktoria’s unusual core design. Despite the simplicity of its appearance, the increased thickness of the slab required substantial work on the special formwork and shoring. Nonetheless, the construction team went above and beyond to adapt to its application quickly. The engineer minimized the constructability challenge by creating a buildable design and working synergistically with the contractor. Even though extra work and concrete were necessary to build Viktoria’s slab/core system, the design created significant savings in material and schedule. Elimination of internal columns produced

numerous benefits, and the design was well-received by the contractor. The owner and architect applied the savings to other aspects of the building that contributed to Viktoria’s market success.

Conclusion The creative use of a unique core drophead system and post-tensioned concrete resulted in an elegantly efficient overall system that pioneered a new approach to concrete building design in high seismic regions. Through careful coordination between the design and construction teams, the building was constructed efficiently and economically and exceeded the expectations of all involved. Viktoria’s drophead system increased the dead load on the lateral system and subsequently reduced drift and tensile reinforcement demands.▪ Cary Kopczynski, P.E., S.E., FACI, is Senior Principal and CEO of Cary Kopczynski & Company (CKC). Mr. Kopczynski serves on the Board of Directors of both the American Concrete Institute (ACI) and PostTensioning Institute (PTI), Chaired the PTI’s Technical Advisory Board for six years, and served on ACI Committee 318 for several building code cycles. Mr. Kopczynski can be reached at caryk@ckcps.com. Joe Ferzli, P.E., S.E., is a Principal at Cary Kopczynski & Company (CKC), located in Bellevue, Washington, and the Senior Project Manager for Viktoria. Mr. Ferzli serves on the Board of Directors of the American Concrete Institute (ACI) Washington Chapter. Mr. Ferzli can be reached at joef@ckcps.com.

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DALLAS FIRE STATION #27 Rebuilding with Site Constraints By Akshai Ramakrishnan, P.E.

Courtesy of Thomas McConnell, Perkins + Will

pon opening its doors in December of 2015, Dallas Fire Station #27 was recognized as special in a number of ways: 1) It is one of only four currently operational multi-story fire station facilities for the Dallas Fire-Rescue Department (DFRD), and the first one built in the last 50 years; 2) Very few fire stations are composed of a concrete frame superstructure; 3) Only a handful of fire stations are LEED registered (Fire Station #27 is currently pursuing Gold certification); 4) No other Dallas fire station has an underground parking garage; and 5) The multiple points of entry required for the apparatus bay is unique, especially when it located at a very busy urban intersection. The structural challenges presented by these last two features are addressed in the following discussion. But first, here is a brief history of how these site constraints developed. Considering the fifty-seven fire stations that the DFRD manages for the city of Dallas, Texas, it can be difficult for an individual station to achieve distinction. With such a long history of service covering a large metropolitan area, the DFRD has utilized dozens of facilities to house their dedicated personnel during more than 140 years of operation. Despite the simplicity, utility, and efficiency these facilities are tailored to meet, an exceptional one pays special homage to the fine men and women who vigilantly maintain the protection of the community as their primary focus. The 23,000 square-foot building did not aim to accomplish each of the feats indicated above purely for the sake of differentiating itself from other facilities. The driving factors for some of these accomplishments were a result of necessity. The original station, which opened in 1948, was a single-story structure of a little less than 5,000 square feet which served the fringes of the growing city of Dallas. However, as the surrounding community began to urbanize, and the quantity of single family and multi-family residences and supporting commercial development increased exponentially, it became apparent the facility needed to be modernized. STRUCTURE magazine

The existing lot encompassed just over 18,500 square feet. To accommodate new quarters, an apparatus bay, parking allotment for firefighters and visitors, and ingress/egress that could meet the minimum requirements for apparatus functionality and access to the street, the primary challenge was already evident. The lot was tucked into the east end of Preston Square, aligned with the southwest corner of the intersection of the Northwest Highway thoroughfare and Douglas Avenue, making the difficult task even more daunting. To the south of the lot (beyond the typical easement) was Berkshire Lane, a public street. Directly to the west of the property

April 2017

was an operating restaurant that, despite accommodating the City as much as possible, required functioning parking spaces and vehicle access to remain operational throughout the duration of demolition and construction activities. The design scheme to accommodate all of the site constraints required building vertically while maintaining grade level access to the apparatus bay to preserve efficient response times. This meant that building a basement level to move the required parking below grade was the most feasible solution. Within this solution, it was deduced that the access ramp would need to be a single entrance/exit ramp so as not to conflict with the apparatus operation, and so as not to limit the quantity of parking spaces available to the eighteen firefighters Station #27 was intended to house. A more than 14-foot deep excavation was required to set the basement level and install the footings supporting the concrete frame and walls. The extent of the 7,500 square foot basement was squeezed into the northeast corner of the site, with basement walls located four feet from the east property line and 13 feet from the north property line. This was to allow the apparatus bay to align on the west side of the building, the foundation of which was to bear on compacted subgrade backfilled against the west basement wall. This facilitated access for apparatus to enter the facility and turn out onto the busy intersection that handles more than 29,000 vehicles per day. Due to such a high traffic count and landlocked site, the excavation required the installation of a temporary earth retention system along the north and east sides of the basement. This allowed for continued use of adjacent roads without restriction throughout the construction. The solution implemented by Ancortex Inc. and AP Engineering Consultant, Inc., was a cantilevered soldier pile retention system with timber lagging, constructed of W6x25 piles embedded six feet into the limestone stratum and encased in a ten-inch diameter grout filled bore spaced at 4 feet on-center. The footing for the east basement wall extended 12 inches beyond the exterior face of the wall but, due to the eccentric loading of the upper-level structure in some locations, the footing extended a minimum of 24 inches from the exterior face of the wall for about 50 feet. As a result, a two-sided forming system by Doka USA was utilized for the basement wall construction, with traditional diagonal strut bracing onto the basement slab to brace for loads imparted by concrete installation and backfill placement between the lagging and the basement wall. This also proved to be a difficult task, as utility easements ran along the east edge of the site and a workable cavity space was required to apply waterproofing. A low strength flowable fill (gravel mixture) was used for backfill because of the lack of space for compaction. The underlying soils at this site consisted of a stiff clay for the upper four feet, weathered tan limestone for the next six feet, and a hard gray limestone layer occurring approximately 10 feet below grade. This soil/ rock profile was a positive, as it allowed the use of shallow footings bearing at the basement level. However, this required excavation of between four to nine feet of limestone materials which necessitated the use of heavy rock excavating equipment. Furthermore, a few (granted simpler) challenges were presented because the apparatus bay slab was bearing on compacted subgrade. The west wall of the apparatus bay was flushed up against the property line adjacent to the restaurant. To maintain similar foundation bearing for the structural cast-in-place concrete wall along this side, drilled concrete piers bearing on the limestone were installed offset from the wall so as to have clearance away from the plat restriction. Eccentrically loaded pilasters were designed with the grade beam placement so that a cold joint could be placed for the wall construction. STRUCTURE magazine

The width of the apparatus bay extended a few feet over the westernmost basement wall, which was constrained due to the two-way access to the parking level. That basement wall required the design of the hydrostatic forces behind the wall (considering a drained condition as perforated drain pipe ran along the bottom of the wall) with an additional surcharge load of 250 psf for the apparatus bay. The north end of the parking garage roof structure extended beyond the footprint of the building above, which presented another challenge. The concrete joist floor structure for the 1st level required a 4-inch depression at the building transition to exterior parking and driveway to accommodate a paver system, and needed to be sloped at 2% grade away from the building. The depth of the structural system was limited to maintain minimum overhead clearance in the garage for vehicles. This resulted in the use of wider joists and narrower pans. To mitigate potential overhead conflicts, building utilities such as fire sprinkler lines were run between the narrow pan joists. Trunk lines were sleeved or cored through the joists. As a result of a portion of the 50,000-pound apparatus being able to turn out over the structured garage roof, the joists and girders in the end bay required that the design apply 2/3 of the load applied on an individual axle and additional analyses involving the moving wheel loads. In summary, Fire Station #27 achieved its primary goal: to provide an efficient and modern facility for the brave firefighters who call it home, while also standing out as a monumental structure that honors all firefighters who protect the city of Dallas.▪

Akshai Ramakrishnan is an Associate of JQ Infrastructure, LLC in the Houston office. He can be reached at aramakrishnan@jqieng.com. The online version of this article contains references. Please visit www.STRUCTUREmag.org.

Project Team Owner: City of Dallas, Texas Structural Engineer of Record: JQ Engineering, LLP, Dallas, Texas Architect of Record: Perkins+Will, Dallas, Texas General Contractor: Bartlett Cocke General Contractors

April 2017

Structural DeSign design issues for structural engineers

he title of ASCE 7-16 is Minimum Design Loads and Associated Criteria for Buildings and Other Structures. This article is the first in a series intended as an introduction to the seismic design of the “other structures,” commonly known as nonbuilding structures.

Types of Nonbuilding Structures Nonbuilding structures are divided into two different categories for seismic design – similar to buildings and not similar to buildings. Nonbuilding structures similar to buildings are designed and constructed with structural systems similar to buildings. Nonbuilding structures similar to buildings also have a dynamic response similar to buildings. A typical nonbuilding structure similar to a building is shown in Figure 1, a pipe rack that uses ordinary moment frames and ordinary braced frames to resist seismic forces. ASCE 7-16, Section 15.5, provides specific requirements for certain nonbuilding structures similar to buildings: • Pipe Racks (15.5.2) • Storage Racks (15.5.3) • Electrical Power Generating Facilities (15.5.4) • Structural Towers for Tanks and Vessels (15.5.5) • Piers and Wharves (15.5.6) Additionally, Section 11.1.3 allows industrial buildings to be treated as nonbuilding structures in certain situations for the purpose of seismic design. Many industrial buildings have geometries and framing systems that are different from the typical occupied structures covered by Chapter 12. The limited occupancy of these buildings reduces the hazard associated with their performance in seismic events. Therefore, when the occupancy is limited to maintenance and monitoring operations, these structures may be designed in accordance with the provisions of Section 15.5 for nonbuilding structures similar to buildings. Examples of such structures include boiler buildings, aircraft hangars, steel mills, aluminum smelting facilities, and other automated manufacturing facilities. Nonbuilding structures not similar to buildings are designed and constructed with structural systems very different from those used in buildings. Nonbuilding structures not similar to buildings also have dynamic response not similar to buildings. A typical nonbuilding structure not similar to a building is shown in Figure 2, an elevated water tank that is a shell structure transferring forces through membrane action. Sections 15.6 and 15.7 provide specific requirements for certain nonbuilding structures not similar to buildings:

Figure 1. A nonbuilding structure similar to a building.

Seismic Design of Nonbuilding Structures Introduction to Designing with ASCE 7-16 By J. G. (Greg) Soules, P.E., S.E. P.Eng., SECB, F.SEI, F.ASCE

J. G. (Greg) Soules is a Principal Engineer with CB&I LLC in Houston, Texas. He is the Vice Chair of the ASCE 7-16 Main Committee, Vice Chair of the ASCE 7-16 Seismic Subcommittee, and Chair of the ASCE 7-16 Task Committee on Nonbuilding Structures. He can be reached at greg.soules@cbi.com.

38 April 2017

Figure 2. Nonbuilding structure not similar to a building.

• • • • • • •

Earth Retaining Structures (15.6.1) Stacks and Chimneys (15.6.2) Amusement Structures (15.6.3) Special Hydraulic Structures (15.6.4) Secondary Containment Systems (15.6.5) Telecommunication Towers (15.6.6) Steel Tubular Support Structures for Onshore Wind Turbine Generator Systems (15.6.7) • Ground-Supported Cantilever Walls or Fences (15.6.8) • Tanks and Vessels (15.7)

Different Treatment of Nonbuilding Structures for Seismic Design The primary differences between buildings and nonbuilding structures are in the occupancy of the structures and the structural systems used. As mentioned above, the limited occupancy of these nonbuilding structures reduces the hazard associated with their performance in seismic events. Nonbuilding structures are designed for higher seismic forces because nonbuilding structures do not incorporate elements that increase damping and ductility typically found in buildings (floors,

diaphragms, non-structural elements). For the same reason, Section 15.4.4 allows the fundamental period of nonbuilding structures to be calculated using the structural properties and deformation characteristics of the structural system of the nonbuilding structure without the restrictions and limits of Section 12.8.2.

Determination of Basic Seismic Parameters The seismic parameters used for the design of nonbuilding structures are the same as those used for the design of buildings with a few exceptions, as noted in the subsequent sections. These seismic parameters are discussed below.

Return Period, Risk, and MCER ASCE 7-16 uses risk-targeted Maximum Credible Earthquake (MCER) ground motions. The MCER ground motions use the different shapes of hazard curves to adjust the uniform hazard ground motions (2-percentin-50-years) such that they are expected to result in a uniform annual frequency of collapse, or risk level when used in design. The risk level targeted in ASCE 7-16 corresponds (approximately) to 1 percent probability of collapse in 50 years. The design ground motion contained in ASCE 7-16 is taken as two-thirds of the MCER ground motion.

Map Values Ss, S1, and TL

SDS, SD1, and the Design Response Spectrum The design response spectrum is defined by SDS and SD1 and is based on 5% damping. Liquid has a much lower damping resulting in higher seismic forces. For most nonbuilding structures, the application of SDS and SD1 is identical to that for buildings. Above ground liquid storage tanks are an exception to this statement. For the convective (sloshing) component in above ground liquid storage tanks, the response spectrum values for the constant velocity region and the constant displacement region are multiplied by 1.5 to convert the values to 0.5% damping.

Risk Category The Risk Category for a nonbuilding structure is defined in Section 1.5 and Table 1.5-1 of ASCE 7-16. Unlike the majority of buildings, most petrochemical structures will fall in Risk Category III or IV based on the Material Safety Data Sheet (MSDS) of the products

Soil Types Soil conditions can amplify the seismic ground motion. ASCE 7-16 defines six different soil types (A-F). If the soil type is unknown, soil type D must be assumed STRUCTURE magazine

stored, unless the hazard assessment provisions of Section 1.5.3 are used to justify a reduced risk category. Many petrochemical structures store large quantities of hazardous materials, thereby requiring a more conservative design approach. The Risk Category affects the importance factor used for the design of the structure, as well as some design and detailing requirements. Table 1.5-2 is used to determine the Importance Factor (IE) value based on Risk Category. The Importance Factor (IE) is used to adjust the level of structural reliability of a nonbuilding structure to be consistent with the classification listed in Table 1.5-1.

Seismic Design Category In ASCE 7-16, the Seismic Design Category (SDC) is a function of Risk Category and soil modified seismic risk in the form of SDS and SD1 and is determined from Tables 11.6-1 and 11.6-2. For a given nonbuilding structure, SDC is determined twice – first as a function of SDS and a second time as a function of SD1. The more severe category will govern. SDC triggers special detailing requirements, especially for foundations. ASCE 7-16 contains an exception to the determination of SDC. This exception allows SDC to be determined from ASCE 7-16 Table 11.6-1 only if the structure is governed by SDS and meets the criteria in Section 11.6. This exception can be applied to nonbuilding structures similar to buildings but not to nonbuilding structures not similar to buildings. continued on next page

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Ss represents the mapped MCER, 5 percent damped, spectral response acceleration at short periods (constant acceleration portion of response spectrum). S1 represents the mapped MCER, 5 percent damped, spectral response acceleration at a period of 1 second (constant velocity portion of response spectrum). TL represents the long-period transition period that separates the constant velocity portion of the response spectrum from the constant displacement portion of the response spectrum. TL varies from 4 seconds to 16 seconds. TL has little effect on the design of building structures but has a major effect on certain types of nonbuilding structures not similar to buildings. TL has a significant impact on the magnitude of the convective force and sloshing wave height in aboveground liquid storage tanks.

(ASCE 7 Section 11.4.2) with a minimum value of Fa equal to1.2. Soil type F requires a site-specific evaluation. A site-specific response analysis is required in the following situations: • Structures on Site Class E sites with SS greater than or equal to 1.0 • Structures on Site Class D and E sites with S1 greater than or equal to 0.2 To account for the different soil types, the MCER ground accelerations SS and S1 are modified by Fa and Fv respectively. Values of Fa and Fv are found in Tables 11.4-1 and 11.4-2.

April 2017

R, Ωo, and Cd Values of R, Ωo, and Cd are located in Table 12.2-1 for building structures, Table 15.4-1 for nonbuilding structures similar to buildings, and Table 15.4-2 for nonbuilding structures not similar to buildings. Chapter 15 Section 15.4.1 allows systems from either Table 12.2-1 or 15.4-1 to be chosen for nonbuilding structures similar to buildings.

Response Modification Factor (R)

by the deflection amplification factor, Cd, to estimate the expected deformations likely to be experienced in response to the design ground motion. Please note that the “reduced design forces” are at a “strength” level. As mentioned above, many nonbuilding structures not similar to buildings are designed using ASD methods. Therefore, any elastic deformations based on ASD level loads must be increased by a factor of 1.4 in addition to Cd.

Redundancy Factor (ρ)

The Response Modification Factor represents the inherent overstrength and global ductility capacity of structural components. Design seismic loads are reduced by R. This reduced design strength level results in nonlinear behavior and energy absorption at displacements in excess of initial yield. In other words, damage (but not collapse) is allowed. Many nonbuilding structures are designed using allowable stress design (ASD) base methods. In many ASD based reference standards, RW is used instead of R. In these cases, RW = 1.4R.

Overstrength Factor (Ωo) The seismic load effect with the overstrength factor is intended to address those situations where the failure of an isolated, individual, brittle element can result in the loss of a complete seismic-force-resisting system or instability and collapse. A special seismic load combination (seismic load effect including overstrength factor) is specified in ASCE 7-16 Section 12.4.3. Numerous documents such as 2016 IBC, ASCE 7-16, 2016 AISC Seismic Provisions, and ACI 318-14 define elements that must be designed for the special seismic load combination. The elements requiring design using the special seismic load combination in buildings also must be designed using the special seismic load combinations for nonbuilding structures similar to buildings. As an example, the struts connecting the transverse moment frames in a pipe rack act as collectors and must be designed for the special seismic load combinations. For nonbuilding structures not similar to buildings, very few elements (e.g. anchor attachment to shells of tanks and vessels) require the use of the overstrength factor in their design.

Deflection Amplification Factor (Cd) The elastic deformations calculated under the reduced design forces (1/R) are then amplified

The Redundancy Factor is a factor intended to penalize structures with little redundancy (lack of multiple load paths) in their lateral force-resisting systems. Rules and exceptions are found in Section 12.3.4. The value of ρ is either 1.0 or 1.3. The value of ρ is always 1.0 for structures in SDC B and C and other structures as defined in 12.3.4.1. For a typical pipe rack, ρ is usually 1.0 or 1.3 in the longitudinal direction (braced frame) and 1.3 in the transverse (moment frame) direction in SDC D through F. The Redundancy Factor is set equal to 1.0 for nonbuilding structures not similar to buildings per the exception listed in ASCE 7-16 Sections 15.6 and 12.3.4.1.

Trade-off between Ductility and Strength In Table 15.4-1, selected nonbuilding structures similar to buildings using “ordinary” structural systems are provided an option where both lower R-values and less restrictive height limitations are allowed. This option permits “ordinary” structural systems that have performed well in past earthquakes to be constructed with fewer restrictions in Seismic Design Categories D, E, and F –provided seismic detailing is used and design force levels are considerably higher. The R-value/ductility trade-off recognizes that the size of some nonbuilding structures is determined by factors other than traditional loadings and result in structures that are much stronger than required for seismic loadings. Therefore, the structure’s ductility demand is much lower than a corresponding building. The R-value/ ductility trade-off also attempts to obtain the same structural performance at the increased heights. The user will find that the option of reduced R-value/less-restricted-height will prove to be the economical choice in most situations due to the relative cost of materials and construction labor. It must be emphasized that the R-value/ductility trade-off of Table 15.4-1 only applies to nonbuilding structures similar to buildings and cannot be applied to buildings.

STRUCTURE magazine

April 2017

Use of Reference Documents Reference Documents are industry standards (such as API 650 – Welded Steel Tanks for Oil Storage) for different nonbuilding structures that have been accepted by ASCE 7 as modified by the provisions of Chapter 15. Reference Documents as used by Chapter 15 do not include material standards such as AISC 341 or ACI 318. Some of the Reference Documents listed throughout Chapter 15 of ASCE 7 have well-defined seismic design procedures. For some of these Reference Documents, ASCE 7 provides “bridging” equations which modify the procedure provided in the Reference Document. These modifications bring the Reference Document up to the same force and displacement level used by ASCE 7. The hierarchy of Reference Documents relative to other codes and standards is not understood by many engineers. The order of precedence is the adopted building code (IBC), then ASCE 7, and finally the reference document (e.g. API 650).

Conclusion This article has provided an introduction to the seismic design of nonbuilding structures to ASCE 7-16. Although there are some exceptions as noted above, most of the core concepts used in the seismic design of buildings apply to nonbuilding structures as well. Key takeaways from this article are: • Nonbuilding structures are divided into two different categories for seismic design – similar to buildings and not similar to buildings. • Nonbuilding structures are treated differently than buildings in seismic design because of the lack of human occupancy and because nonbuilding structures do not incorporate elements that increase damping and ductility (floors, diaphragms, non-structural elements) typically found in buildings. • The presence of liquid in many nonbuilding structures requires the modification of the ground motions used for design. • The trade-off between ductility and strength is unique to the seismic design of nonbuilding structures similar to buildings. • Many nonbuilding structures rely on the use of Reference Documents for their seismic design. A follow-up article will cover advanced topics in ASCE 7-16 seismic design of nonbuilding structures and nonstructural components.▪

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Historic structures significant structures of the past

ngineers knew for years that making spans continuous over piers could save a significant amount of wood, iron, or steel over that required for a series of simple span bridges. In fact, wooden bridge builders like Timothy Palmer, Theodore Burr, Ithiel Towne, Stephen Harriman Long, and others frequently built their spans continuous over the piers. They had only their intuition and experience to arrive at a design. Long, however, gave the matter serious thought and wrote about it in his pamphlet on bridge building, Directions to Builders of the Jackson Bridge. In it, Long gives the first indication that he indeed does have some “approved rules” for designing a continuous bridge. For the upper and lower chords he wrote: “…they should be equal to each other in their transverse dimensions and initial strength. …wherein …the perfection of the plan of construction before us, consists in such an arrangement of the strings as will subject them to equal action in sustaining a load upon the bridge.” He said that this was to be accomplished by: “…rendering the upper strings continuous, over the piers and abutments, in such a manner that a degree of tension may be exerted at those points equal to that exerted by the lower string, at points intermediate to the spans, and vice versa, that the degree of thrust exerted by the lower strings against the piers and abutments, may be equal to that exerted by the upper strings, at the intermediate points as above.” In other words, he made his trusses continuous over the intermediate supports so that the maximum positive moment over the support is equal, or nearly so, to the maximum negative moment located between the supports. He continued: “…the reciprocity of the actions of the upper and lower strings, here adverted to should be aimed at in all bridges whose spans exceed 120 or 130 feet; but need not be particularly regarded in bridges of less extent: inasmuch, as the tension in the lower, and the thrust in the upper strings, may be effectually counteracted without increasing the dimensions of the pieces to an unwieldy size.” To achieve this equality of load in the upper and lower chords he wrote: “…in dividing the breath of a river into spans for a bridge, except the exterior spans, or those contiguous to the contemplated abutments, which should have only about three-fourths the extent of the other spans. The reason for this will be obvious from a recurrence to the principle of double action in the strings...the centre posts of the truss frames for the exterior

Lachine Rapids Bridge By Frank Griggs, Jr., Dist. M.ASCE, D.Eng., P.E., P.L.S.

Dr. Frank Griggs, Jr. specializes in the restoration of historic bridges, having restored many 19 th Century cast and wrought iron bridges. He was formerly Director of Historic Bridge Programs for Clough, Harbour & Associates LLP in Albany, NY, and is now an Independent Consulting Engineer. Dr. Griggs can be reached at fgriggsjr@verizon.net.

42 April 2017

spans must be located not at the centre of the spans, but at a point distant from the abutment about 1/3 part of the length of the exterior span.” As a result of this experimentation, the effect of continuity on the stiffness of beams was known intuitively for some time. Robert Stephenson built his famous tubular bridge across the Menai Straits in Wales continuous over three central piers in March 1850. However, no one in the United States, or for that matter in Europe, had developed an analytical method for determining the reactions of a continuous beam, the moments over the piers, or the maximum moment between the supports until the Theorem of Three Moments was developed by Benoit Clapeyron in 1857. The Theorem was updated by Mohr in 1860 to include settlements of the supports. These equations, however, included a value for the modulus of elasticity, E, and moment of inertia, I, of each span and normally did not permit any settlement of the piers that could increase the moments the spans would have to resist. The assumption that E and I were constant over all the spans reduced the complexity of the equations, making it easier to determine the moments over the piers and thus the reactions. With reactions known, the moment at any point along the spans could be identified and the member sized appropriately. Some engineers also worried about the effect of temperature changes on the member loads and stresses. The reason many engineers did not use continuous spans was that, at the time, they had little confidence that E was constant nor that I was constant over the length of the spans. They also worried that any settlement would add to the moments the spans would have to resist. These factors were taken into consideration by C. Shaler Smith (STRUCTURE, August 2008) when he was called to design a railroad bridge across the St. Lawrence River at the Lachine Rapids near Montreal. Smith had already built his famous Kentucky High Bridge (STRUCTURE, August 2015) as a continuous truss during erection but, by cutting the lower chords at two points, he converted it into a cantilever truss. The fact that the base of the river was solid rock eliminated, in his mind, the settlement problem. This would be Smith’s last major bridge project, built for the Canadian Pacific Railroad looking to extend its line to the east and across the St. Lawrence River near Montreal in January 1882. The first bridge plan proposed consisted of “ten deck spans of 300 feet in the clear and one through span of 330 feet with a clear headway of 60 feet above ordinary summer water. The bottoms of the deck spans were placed 30 feet above ordinary summer water.” The bridge would cross the Lachine Canal and the Grand Trunk Railway, as well as the St. Lawrence River just upstream from the Lachine Rapids. A revised plan was submitted

Smith’s proposed designs.

to the government “with 12 spans of 250 feet and one of 330 feet.” This was not satisfactory with the river men, mainly those who ran log rafts down the river, so the Chief Engineer for the railroad, P. Alexander Peterson, agreed to a plan with “11 spans of 268 feet and one span of 340 feet.” It was not until the summer of 1884 that Peterson called in C. Shaler Smith as consulting engineer. Upon reviewing the site, he was worried about building piers in the St. Lawrence and proposed “there should be introduced two spans of 258 feet and two spans of 408 feet over the channel, thus getting rid of one deep water pier, and probably one

years time in the construction of the bridge.” The two 408-foot spans would be erected on the cantilever principle with 258-foot spans serving as anchor spans. Smith considered three schemes of building the channel spans (see diagram). The top plan was for a bridge with two piers in the main channel and pins inserted at points of contra flexure, making it a cantilever with all reactions determinate. The middle plan was for a single pier in the main channel and pins again inserted in the lower chords and a top chord peaking over the center span, making it also a cantilever with all forces determinate. The

last alternative was selected with the 408-foot spans and flanking 269-foot 10-inch spans being continuous. Smith decided to build a continuous truss saying, “when the connection is made in the centers of the cantilever spans, the joints are to be riveted up so that they will act as cantilevers for dead load and as continuous girders for live load.” All expansion and contraction movements were to be taken up in the ends of the flanking or anchor arms that were on rollers or rockers with tension links holding down the ends during the cantilevering process. Tenders (proposals) were called for in September 1885 on two different plans. A complete specification for the bridge contained a section on span length, which stated: “The plans show the piers of the bridge over the St. Lawrence arranged in two different ways; No. 1 arrangement has eight spans of 242 feet center to center of piers, two spans of 269 feet 10 inches center to center, and two spans of 408 feet. No. 2 arrangement has nine spans of 268 feet, two spans of 269 feet, and one span of 340 feet center to center: but tenders and plans will be received for any other arrangement providing the position of the east pier of the channel span was not changed, and

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April 2017

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that no piers were placed closer than 242 feet center to center.” Plan No. 1 was adopted, and the erection process on the four central spans consisted of first building the 269-foot 10-inch anchor spans on falsework. The channel spans were then cantilevered out 10 panels from each anchor span using conventional techniques. The new twist in the erection was to build cantilevers out each way from the central pier. This “was known in Mr. Smith’s office as the ‘Flying Cantilever,’ and was first proposed for the Storm King Bridge over the Hudson River, in the State of New York.” A short, temporary falsework was built from the central pier to support the first panel point in each direction. After the construction of these two panels, the spans were built out equally with a traveler moving in each direction and great care taken to keep the spans in balance. Also, cables were strung from the completed cantilevered spans to help maintain the central portion in a stable position throughout the construction of the eight closing panels. The single track bridge was completed successfully and opened to traffic in July 1886. The trusses were Whipple Double Intersection and pin connected. The appearance of the bridge created a great deal of discussion in the journals of the day. The Railroad Gazette reported:

“There are a great number of such combinations of through and deck span throughout the country, and surely will be more. Their ugliness results, of course, from the sharp break in the continuity of the lines of the structure, which destroys all dignity and pleasing effect, and gives them a flimsy and makeshift look. Whether giving to the through spans the form of a bastard arch which is not Lachine Rapids Bridge under construction and completed. an arch is any real remedy may plausibly be disputed, but we are inclined steel were high enough to risk the increases to think that the design shown will be genin loads and stresses in the truss members erally considered a more pleasing, or rather due to the unknown possible effects of varialess ugly, solution of the problem than the tions in E, I, the settlement of foundations, ordinary form, and so, on this ground and temperature. alone, worthy of use in such localities.” The bridge was replaced in 1913, due to It was erected by the Dominium Bridge increased loading, with two parallel simple Company under the leadership of Job Abbot span bridges each carrying one track. Since (STRUCTURE, April 2012). Smith was it was not possible to stop traffic during convirtually on his deathbed during bridge construction, they expanded most of the piers struction and died shortly after its opening downstream and built a new single track on December 19, 1886. For 29 years, it was bridge on the expanded piers. This was folthe only major continuous bridge in the lowed by removing the old bridge spans and America’s. Many engineers were still reluc- building another single track bridge on the tant to believe that the savings in iron and existing portion of the piers.▪ ADVERTISEMENT–For Advertiser Information, visit www.STRUCTUREmag.org

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Professional issues

issues affecting the structural engineering profession

Overall Career Satisfaction, Development, and Advancement Structural Engineering Engagement and Equity (SE3) Committee Survey Results By Angie Sommer, S.E. and Rose McClure, S.E.

he mission of the Structural Engineering Engagement and Equity (SE3) Committee of the Structural Engineers Association of Northern California (SEAONC) is to study and improve engagement and equity in the structural engineering profession. In early 2016, SE3 administered a nationwide survey of practicing and formerly practicing structural engineers. The effort received over 2,100 completed responses. The survey questions aimed to investigate overall career satisfaction across a range of metrics, including career development, trajecFigure 1. tory, and advancement; compensation, benefits, and flexibility; work environment and Overall Career Satisfaction work-life balance; and the effects of caring for children or other dependents. One of the career satisfaction questions This article highlights survey findings regard- asked: “How satisfied are you with your ing overall career satisfaction, development, choice of a career in structural engineerand advancement. A full report that includes ing?” Respondents overwhelmingly answered findings on compensation and work-life bal- positively, with 81% reporting “satisfied” ance can be found at SE3project.org. or “very satisfied” and only 8% reporting “dissatisfied” or “very dissatisfied” (Figure 4). Demographic Overview of However, when asked if they had ever considered leaving the profession, 56% of the Survey Respondents respondents responded affirmatively. • 2,161 completed responses were The survey responses suggest that overreceived from currently and formerly all career satisfaction stems from a variety practicing structural engineers. of sources, including pay/compensation, • Responses were received from 46 work-life balance, career advancement, and states, as shown in Figure 1, though work environment. Of these factors, men approximately half of the responses and women cite distinctly different sources were from California. for their satisfaction (or lack thereof ), as do • 7% of the respondents were formerly respondents of varying ages and positions. practicing structural engineers who had Overall, three factors that correlated strongly left the profession or retired. among those who reported the highest satis• Respondents were relatively wellfaction with their career were: distributed among position titles, as shown in Figure 2. • 52% of the total respondents had children. By gender, 57% of men had children, while only 38% of women had children. • Nearly 50% of the respondents were under the age of 35. • 40% of the respondents had an SE license, 73% had a PE license, and 76% had an EIT certificate. • 29% of the respondents were women, as shown in Figure 3. Figure 2. STRUCTURE magazine

April 2017

• Holding more senior positions within their companies • Being assigned daily tasks that align with their career objectives • Being a parent

Reasons for Leaving the Profession Men and women both reported that their top reasons for considering leaving the profession were to seek better worklife balance, less stress, and higher pay. Women rated work-life balance highest among these factors, while men rated pay as their top reason (Figure 5). For respondents who had left the profession (not including those who had retired), the findings were similar, but with the addition of one notable reason: poor management/leadership.

Career Development Thirteen percent of respondents indicated being “dissatisfied” or “very dissatisfied” with their career development, which includes daily activities and job responsibilities, professional development opportunities, and career advancement. While most respondents were relatively satisfied with their career development, some significant findings were revealed regarding this topic, including differences in perceptions between managers and staff, the benefits of mentorship, and variations based on gender. Management vs. Staff Perceptions Managers and staff have notably different perceptions of expectations for advancement and the work environment. Compared to all other position levels, principals/owners are 43% more likely to “agree” or “strongly agree” that

Figure 3.

Figure 4.

expectations for advancement are effectively communicated in their firms. Similarly, when evaluating opportunities for advancement, principals/owners are 24% more likely than all other staff to believe that equal opportunities for advancement exist in their firms. Principals/owners are also less likely than all other staff to believe that formal business management training is essential. This is in stark contrast to a recent study that found that 98% of managers in the United States feel that more management training is needed in their own firms. In the study, 87% percent of those surveyed wish they had received more management training before assuming their current roles, and those same managers agreed that companies need to develop better ways to evaluate managerial ability (Grovo, 2016).

Additionally, aligning employees’ daily tasks with their career objectives was found to be one of the factors most highly correlated with satisfaction, indicating that employees would be better served if this were a prioritized goal for management. Respondents who experienced this alignment were significantly less likely to consider leaving the structural engineering profession. This finding applies to both men and women. Mentorship Respondents with identified mentors reported being more satisfied with their career advancement/trajectory and overall career choice than those without a mentor. Of the 1,943 engineers who responded to questions regarding mentorship, over half (55%) indicated that they had at least one mentor who strongly influenced their career path. Eighty-three percent of respondents who have a mentor reported being “satisfied” or “very satisfied” with their career advancement/trajectory, while only 67% of respondents without a mentor reported the same. Men and women reported having mentors at roughly equal rates. People who did not indicate having mentors were 22% more likely to consider leaving ADVERTISEMENT–For Advertiser Information, visit www.STRUCTUREmag.org

STRUCTURE magazine

April 2017

Figure 5.

the profession. This is consistent with comprehensive research that documents the benefits of mentorship. One recent study by the Society of Women Engineers highlights the benefits to both employers and employees, noting that mentorship often facilitates a sense of connectedness to the organization, increases satisfaction, and reduces turnover (Amelink, 2008). continued on next page

CAREER ADVANCEMENT YEARS TO

15.5 11.1

PRINCIPAL V.

ASSOCIATE V.

14.7 13.9

SENIOR ENGINEER

9.0

10.8

PROJECT ENGINEER

3.6

3.7 m

Figure 6.

Gender Differences Men were 20% more likely than women to agree that opportunities for advancement are equal across genders. However, women were 23% more likely to be dissatisfied with their career advancement than men. This effect

increased over time; for each year of experience, women were signiﬁcantly less likely to report being satisﬁed with their career progress. However, the data showed that women advance at a faster rate than men for all positions except principal/owner. As shown in Figure 6, the average number of years that it took for Figure 7. female respondents to reach the senior engineer/project manager position was 9.0 years, while male respondents reached this position, on average, in 10.8 years. Similarly, female respondents reached the associate/ shareholder level in 11.1 years, while males achieved this level in 13.9 years, on average. At the principal/owner level, however, it took female respondents 15.5 years, on average, to attain this title, while male respondents reached this level after only 14.7 years. Despite the apparent faster rate of advancement of the women surveyed, the number of women decreases significantly at each successive position. The highest ratio of women to men occurs at the staff/entry level (39% women) and the lowest ratio occurs at the principal/owner level (16% women), as shown in Figure 7.▪

Angie Sommer is an Associate at ZFA Structural Engineers in San Francisco, California. She is the primary author of the 2016 SEAONC SE3 Survey Report and is the 2016-17 co-chair of the SEAONC SE3 Committee. She can be reached at angies@zfa.com. Rose McClure is a Senior Engineer at Simpson Gumpertz & Heger in San Francisco, California. She co-founded and co-chaired the SE3 project with Natalie Tse in 2015/16. She can be reached at rfmcclure@sgh.com. The online version of this article contains references. Please visit www.STRUCTUREmag.org.

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InSIghtS

new trends, new techniques and current industry issues

Building Official’s Expectations

Deferred Submittals

By Chris Kimball, S.E., P.E., MCP, CBO

ike it or not, design professionals are required to deal with building officials on a regular basis. This is such an important aspect of structural engineering that NCSEA has a committee devoted to it – the Code Officials and Government Agencies Committee. Several member SEA’s also understand the importance of the relationship that structural engineers should have with building officials. A great example is a white paper entitled Guideline – Structural Plan Review Philosophy that was developed by the Structural Engineer’s Association of Washington (SEAW) with the help of the Washington Association of Building Officials (WABO) and is located on the WABO website. Structural engineering firms should understand the importance of working collaboratively with the building official during the plan review process and should ensure their engineers respect this relationship. It is important to remember that we are on the same team trying to make sure that the final product meets code, is safe for the public, and that a good product is provided to the owner. Structural engineers should take into account the following items before submitting documents for a building permit.

Attitude The most important thing to keep in mind is to maintain your composure. Be professional and treat the building official, and his or her staff, in a professional manner. The plan review comments that are provided might seem silly or ridiculous to the engineer of record, but remember that everyone sees things differently and a building official’s background is not the same as a design professional’s. Also, while you might have hundreds of hours poured into a design, the jurisdiction is only provided a few short hours to review what is provided. Be patient and respond to plan review comments in a tactful manner. This includes clouding changes made to the plans and providing direct references to the revised sheet number or calculation page numbers. A better relationship and a level of mutual respect can be established with the jurisdiction if extra time is taken to provide clarity in your response letters.

Supporting Calculations Calculations should be provided to support the design contained within the construction documents. These calculations should be performed in reference to the adopted building code and current standards that are listed in Chapter 35 of the International Building Code (IBC). Perhaps the most common plan review comment made by building officials is the need to update calculations, as they might reference outdated codes or referenced standards. Try not to rely too much on engineering judgment and ensure that calculations are provided for all major structural elements. When engineering judgment is used, provide a clear and concise explanation that justifies the approach. Considerations for structural irregularities, combined lateral systems, redundancy, etc. should be clearly identified within the calculation package. For example, if the building in question has an obvious re-entrant corner, the calculations should note how the 25% increase required by Section 12.3.3.4 of ASCE 7 was taken into consideration. This will help to avoid a general plan review comment where it may not be clear to the building official how the re-entrant corner was addressed in the design.

Statement of Special Inspections (SSI) Section 1704.3 of the IBC states that the “… design professional in responsible charge shall prepare a statement of special inspections.” This SSI should be specific to the project and not just list the materials to be inspected, but provide a clear breakdown as to the extent of the inspections and testing to be performed. It should also note the frequency of those inspections and tests. This has become increasingly difficult, as many of the special inspection requirements are now provided in referenced standards rather than in Chapter 17 of the IBC. The special inspection requirements covered in Chapter 17 of the IBC are critical to the building official. The Structural Engineer of Record (SER) should take extra time to ensure that a specific SSI is created for each project.

The IBC defines deferred submittals as “those portions of the design that are not submitted at the time of the application and that are to be submitted to the building official within a specified period.” Three items should be pointed out in regards to deferred submittals. 1) It is important to understand that the Building Official is not required to allow deferred submittals. Section 107.3.4.1 of the IBC requires the Building official’s approval for all deferred submittals. Some items that may not be allowed as deferred submittals could include prefabricated metal buildings, deep foundation elements, seismic restraint of nonstructural components, etc. 2) All structural deferred submittals must be reviewed by the SER before submission to the Jurisdiction. The SER should ensure that the deferred submittal design is in general conformance with their design of the structure and then place a notation on the submittal noting such. No deferred submittals should be provided to the jurisdiction without a notation from the SER. 3) All too often items, are deferred and then installed without being submitted to the jurisdiction for their review and approval. If the SER notes on the plans that an item is to be deferred, they should ensure that those items are properly submitted to the jurisdiction for approval.

Conclusion As the SER, there are several steps you can take to help make a potentially uncomfortable process a smooth and beneficial one. Please remember that both the SER and the Building Official share a common goal. They are each trying to ensure that the structure is safe and that a good product is provided to the owner. In summary, work together in a professional manner, provide appropriate calculations, include a project-specific SSI, and be careful when including deferred submittals for a portion of the project.▪

Chris Kimball is the Utah Regional Manager for West Coast Code Consultants, Inc. Mr. Kimball provides plan review services to many jurisdictions throughout the Western United States in addition to providing building code training to design professionals, building officials, and to contractors. He can be reached at chrisk@wc-3.com.

STRUCTURE magazine

April 2017

Building Blocks

updates and information on structural materials

Environmental Product Declarations Steel Industry Issues First EPDs for Steel Joists and Steel Decks By J. Kenneth Charles, III and Robert C. Paul, P.E.

hinking green is not enough in today’s construction environment. Any person or company can claim to be sensitive to the environment, but are their products and processes sustainable? With increased demand in the design arena for sustainable building practices and materials, architects, engineers, and other “buyers” can have a difficult time assessing the various parts and pieces that go into any construction project. They are confused by labels that are not standardized. There must be transparency and verifiability if these design professionals are to end up with truly sustainable projects that meet clients’ demands. In 2013, the Steel Joist Institute (SJI) was challenged, as members of the Steel Construction Sustainability Council, to consider the development of Environmental Product Declarations (EPDs) for steel joists and steel decks. The Steel Construction Sustainability Council is comprised of steel partner organizations that meet twice per year to review trends and challenges in sustainable building practices. It was founded by the Steel Market Development Institute, a business unit of the American Iron and Steel Institute (AISI). The first task was to understand the various terms and definitions discussed by the Council. Steel is the most recycled material on the planet, but there are also other important considerations when determining a product’s sustainability, such as: • Product Category Rule (PCR) – Product Category Rules put in place the rules of the game for the development of Life Cycle Assessments (LCAs) and EPDs. The PCR defines how the EPD are created for a specific product, including how system boundaries are chosen, which impact categories should be included, and which methodologies should be used. • Life Cycle Assessment (LCA) – This concept originally developed in the 1960s and 1970s. It assesses the inputs, outputs, and environmental impacts of a product or system over its entire lifespan, from extraction of raw materials to end-of-life disposal or recycling.

• Life Cycle Inventory (LCI) – This term refers to the data collection portion of the LCA. An LCI accounts for all inputs and outputs related to the system being studied. • Environmental Product Declaration (EPD) – An EPD is defined by thinkstep, a prominent Life Cycle Assessment practitioner, as: “a verified (and registered) document that communicates transparent and comparable information about the life cycle environmental performance of a product.” The EPD is the vehicle for reporting the results of the LCA studies.

Moving Toward Transparency SJI and the Steel Deck Institute (SDI) share several member companies, so it made sense to move ahead as a team in the development of EPDs for these products. UL-Environment (UL-E) was selected as the Program Operator, and thinkstep was chosen as the Life Cycle Assessment Practitioner. The first step in the process was determining which data should be collected from the steel joist and steel deck manufacturers, and which plants would supply the information based on processes that could be found at any SJI or SDI member plant. This was necessary for the resulting EPD to reflect an industry average. Thinkstep collected the data and conducted the LCA study, which covers everything from materials and energy to paint, chemicals, and packaging. The results include quantities of waste and materials for recovery, emissions for air and water, ozone depletion potential effects, and potential global warming contributions. The collected data represents more than 85% of the products manufactured in North America by SJI and SDI member companies. After the LCA study had been completed, an independent review was conducted. When the study had passed the review process, thinkstep created the EPDs, titled Environmental Product Declaration: Open Web Steel Joists and Environmental Product Declaration: Steel Roof Deck and Steel Floor Deck. The documents were sent to UL-E for third-party verification. The final step was registering the EPDs with UL-Environment.

STRUCTURE magazine

April 2017

The resulting EPDs for both steel joists and steel deck are available for free download. Open Web Steel Joists can be downloaded from the Steel Joist Institute website (www.steeljoist.org), and Steel Roof Deck and Steel Floor Deck can be downloaded from the Steel Deck Institute website (www.sdi.org). Both EPDs are also included on the UL website (www.ul.com). To download from the UL site, scroll down to the bottom of the page. In the Resources column, click on Sustainable Product Guide and then look for the Steel Deck Institute and the Steel Joist Institute under the Manufacturers/Brands tab. This new data is also included in thinkstep’s GaBi databases (www.thinkstep.com) and the Tally database (http://choosetally.com). Construction professionals interested in viewing and using steel industry EPDs and other transparency resources in their building projects can visit www.buildusingsteel.org for a list of steel product EPDs and updates on other sustainability resources.

LEED v4 Benefits for Building Construction Professionals The EPDs enable engineers, architects, designers, specifiers, and other construction professionals to include steel joists and steel decks as separate products toward the achievement of one point in LEED v4, using the Materials and Resources credit titled Building Product Disclosure and Optimization – Environmental Product Declarations. Open web steel joists, and steel floor and steel roof deck, have always been environmentally responsible products. With the development of Environmental Product Declarations voluntarily undertaken for these products, scientific data and results now exist to assist design professionals in the materials selection process. Through this process, the steel industry continues to demonstrate its commitment to transparency in sustainability reporting methods.▪ J. Kenneth Charles, III is Managing Director of the Steel Joist Institute (https://steeljoist.org). He is based in Florence, South Carolina and can be reached at kcharles@steeljoist.org. Robert C. Paul is Managing Director of the Steel Deck Institute (www.sdi.org). He is based in Glenshaw, Pennsylvania and can be reached at bob@sdi.org.

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business issues

CASE BuSinESS PrACtiCES

Foundations for Risk Management – They Still Matter By Brent White, P.E., S.E.

ur everyday lives are fraught with elements of risk – driving our children to school or ourselves to work, walking on the sidewalk, or even the public places we frequent. As practicing structural engineers, we deal with risk every day. The nature of our profession is to utilize our understanding of risk and mitigate it based on our experience, knowledge, and mastery of science and engineering principles. We design structures and structural systems that provide for the public welfare (safety) as well as achieving the functional and financial goals of our clients. Our engineering practices are inherent with risks that are part of the nature of our profession. When the risks are recognized and understood, methods to reduce risk can be employed. Over ten years ago, the Coalition of American Structural Engineers (CASE) recognized the need for additional tools that engineers could use to reduce risk. The CASE Risk Management Program was established to develop those tools, guidelines, and other activities. The Foundations for Risk Management were established and presented as a basis upon which to build useful tools. In an article published in STRUCTURE magazine (August 2005), Doug Ashcraft from CASE outlined and detailed the Foundations for Risk Management and the basis for their implementation. The published Foundations for Risk Management are described in the attached sidebar. As stated in 2005, “Structural Engineers have the highest claims-to-revenue ratio among practitioners in the Architectural/ Engineering field.” The 2015 Professional Liability Insurance Survey of member firms conducted by ACEC reinforces that this is still the case, with mean premiums for structural engineering firms double that of any other engineering discipline. Premiums reflect the claims losses covered by insurance. Recent insurance claim information shows that 48% of claims against structural engineers are due to design errors of some type and 21% are due to construction defects (Risk Drivers, XL Catlin, 2013). The disproportionate claim amounts for SE’s and increased premiums for structural engineering firms indicates we still have work to do in reducing risk exposure. Recently, the CASE Executive Committee has reviewed the Foundations for Risk Management (10 Foundations) to determine

if they are all still relevant considering the ever-changing nature of engineering practice. Engineering principles may not change, but practices do as knowledge and technology advance. The Executive Committee determined that the 10 Foundations are as relevant today as when they were established. A few minor adjustments have been made to sub-headings, but they still form the basis for the tools and products that CASE has and will develop. Since the Foundations for Risk Management were introduced, CASE has added to its existing library by providing additional contracts, guidelines, and tools to assist firms in reducing risk. All additional works continue to be based on the 10 Foundations. Currently, the CASE library contains 15 contracts, 16 guidelines and white papers, and 28 tools, all of which are available to CASE members for free and to all engineering firms for purchase. Recently added guidelines include Guidelines for International Building Code-Mandated Special Inspections and Tests and Quality Assurance (Foundations 6 – Scope, and 10 – Construction Phase) and Self-Study Guide for the Performance of Site Visits During Construction (5 – Education, and 10 – Construction Phase). Tool 10 – 1 Site Visit Cards (10 – Construction Phase) was recently updated to by adding additional content to assist the engineer during site observation visits. The contracts, guidelines, and tools vary in topic and content, but all are based on the risk management foundations. National Practice Guidelines for the Structural Engineer of Record is one of the first guidelines developed and published, and remains one of the most popular publications. This guideline has been updated multiple times to stay current and is very valuable as a reference when developing scopes of service. A Guide to the Practice of Structural Engineering is an interactive tool that is very helpful in developing young engineering talent. An Agreement for the Provision of Limited Professional Services is a basic form of agreement that can be extremely useful for small projects with a very limited scope of service. These documents are just three examples of popular publications that would likely be of use to most structural engineering firms. For success in any endeavor, a clear foundation and direction are essential. CASE believes

STRUCTURE magazine

April 2017

Foundations for Risk Management 1. Culture Create A Culture Of Managing Risks & Preventing Claims 2. Prevention & Proactivity Be Proactive with Preventive Techniques, Don’t Just React 3. Planning Plan To Be Claims Free 4. Communication Communicate to match expectations with perceptions. 5. Education Educate all of the Players in the Process 6. Scope Develop and Manage a Clearly Defined Scope of Services 7. Compensation Prepare & Negotiate Fees that Allow for Quality and Profit 8. Contracts Negotiate Clear & Fair Agreements 9. Contract Documents Produce Quality Contract Documents 10. Construction Phase Provide Services to Complete the Risk Management Process The full detail for each foundation can be found at www.acec.org/case/news/publications. that the Foundations for Risk Management can provide support for our firms as we identify, evaluate, and mitigate risk in our engineering practices. For more details regarding each foundation and a downloadable pdf of the Foundation for Risk Management, go to www.acec.org/case/ news/publications. For further information regarding membership or to participate in CASE, please refer to the CASE website www.acec.org/case or contact Heather Talbert, htalbert@acec.org.▪ Brent White is the President of ARW Engineers in Ogden, Utah. He serves as the chair of the CASE Toolkit Committee and is a past-president of the Structural Engineers Association of Utah. He can be reached at brentw@arwengineers.com.

GINEERS

ASS O NS

STRUCTU

OCIATI

RAL

COUNCI L

NCSEA News

News form the National Council of Structural Engineers Associations

NATIONAL

2017 NCSEA Corporate Members NCSEA recognizes and thanks its Associate, Affiliate, and Sustaining members as well as its partnering organizations for their continued support in 2017.

Associate Members AISC American Wood Council Bentley Systems, Inc.

Insurance Institute for Business & Home Safety

Simpson Strong-Tie

International Code Council

USG Corporation

Steel Tube Institute

Precast/Prestressed Concrete Institute

Fabreeka International

Metal Building Manufacturers Assn.

Five Star Products

Affiliate Members Alpine TrusSteel

Freyssinet, Inc.

Pieresearch

Atlas Tube

Geopier

RISA Technologies

AZZ Galvanizing

Headed Reinforcement Corp. (HRC)

Scia Inc.

Bekaert

Hilti, Inc.

SE Solutions, LLC

Blind Bolt

Steel Deck Institute

Cast Connex Corporation

ITW Commercial Construction North America

Cold-Formed Steel Engineers Institute

Lindapter USA

Strand7

Construction Tie Products, Inc.

Mitek Builder Products

DECON USA

New Millenium Building Systems

DeWalt

Performance Structural Concrete Solutions

Steel Joist Institute Trimble

Sustaining Members ARW Engineers

Gerald E. Kinyon

Morabito Consultants, Inc.

Barter & Associates

Gilsanz Murray Steficek

O’Donnell & Naccarato, Inc.

Blackwell Structural Engineers

Glotman Simpson Consulting Engrs

Omega Structural Engineers, PLLC

Burns & McDonnell

The Harman Group, Inc.

Professional StruCivil Engineers, Inc.

Cartwright Engineers

The Haskell Company

Ruby & Associates, Inc.

Collins Engineers, Inc.

Holmes Culley

SES Group LLC

Cowen Associates Consulting Structural Engineers

James Ruvolo

Simpson Gumpertz & Heger Inc.

Criser Troutman Tanner Consulting Engineers

Joe DeReuil Associates

Sound Structures, Inc.

Jon Brody Structural Engineers

Stability Engineering

KBR

Structural Engineers Group, Inc.

Krech Ojard & Associates

STV, Inc.

L.A. Fuess Partners

TGRWA, LLC

LBYD, Inc.

Thornton Tomasetti

LHB Inc.

Wallace Engineering Structural Consultants, Inc.

CTL Group DCI Engineers Degenkolb Engineers DiBlasi Associates, P.C. Dominick R. Pilla Associates DrJ Engineering

Mainland Engineering Consultants Martin/Martin, Inc.

ECM Engineering Solutions, LLC

Mercer Engineering PC

A listing of these members, including contact information, can be found at www.ncsea.com/members. To become an Associate, Affiliate or Sustaining member of NCSEA contact Susan Cross at 312-649-4600, ext. 204, or scross@ncsea.com.

Partnering Organizations CASE

SEI

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April 2017

For the third year in a row, NCSEA is pleased to offer the Grant Program to our Member Organizations. This program has been developed to assist Member Organizations in growing and promoting their organization as well as, the structural engineering field, in accordance with our Mission Statement: NCSEA advances the practice of structural engineering by representing and strengthening its Member Organizations. Since implementation in 2015, NCSEA has been able to award 13 grants Member Organizations. These grants have helped fund women’s groups, attendance to SE review courses, educational forums, and other diverse activities. 2017 Grant Applications are now being accepted and can be found on www.ncsea.com. Applications are due August 1st and the winners will be announced at the NCSEA Structural Engineering Summit in October.

News from the National Council of Structural Engineers Associations

Previous grant recipient projects included: • SEAoI for $3,000: Improving SEAOI’s Women’s Networking Initiative to include two new events that will help women structural engineers in the Chicago area network and grow in their careers. • OSEA for $2,000: Supporting the pilot program of Engineering Alliance for the Arts in Tulsa. • SEAoA for $3,000: Helping the Young Member Group provide SE Review sessions, activities with Habitat for Humanity and Future Cities, technical tours, and networking opportunities.

• SEAMW for $2,000: Developing an outreach program directed to undergraduate & graduate students. • SEAKM for $1,500: Enhancing the student chapter programs at Kansas State University, the University of Kansas, and the University of Missouri-Kansas City. • SEAOT for $3,000: Setting up an Engineers Alliance for the Arts Student Impact Project at a Houston High School. • MNSEA for $1,000: Funding for a Structural Engineering Breakfast Forum with presentations and panel discussions for University of Minnesota engineering students. • SEAKM for $1,000: For the Kansas State University Chapter of SEAKM to send students to structural engineering conferences throughout the U.S. • SEAOI for $2,670: For a technology package to improve the quality and quantity of online programming. • SENH for $3,000: To help the Young Members Group host an SE Exam Review, participate in student outreach, and work with Habitat for Humanity. • SEAMW for $2,000: To host a Pecha Kucha Dinner Event and Presentation developed by the Young Members. • SEAC for $3,000: For an expansion of educational programming to project presentations, job site tours, and plant tours. • SEAU for $5,000: Update the 25-year-old Snow Load Study.

NCSEA News

NCSEA Grants Program

For more information, visit www.ncsea.com.

2017 STRUCTURAL ENGINEERING SUMMIT October 11–14, 2017 Washington Hilton . Washington, D.C.

Young Member Awards NCSEA is offering awards to young members belonging to a Structural Engineers Association Young Member Group to help them attend the annual NCSEA Structural Engineering Summit. The awards are divided into two categories: Young Member Scholarships This awards the recipient full registration to the Summit as well as a stipend for additional costs. Young Member Group of the Year This awards three finalists a free registration for a representative to attend the Summit where the winning groups will be announced and awarded an additional prize to fund future activities. The deadline for applications is May 26. For more information on these awards, past winners, and the applications, visit www.ncsea.com.

NCSEA Committee Openings NCSEA committees are accepting new members. Members of State Structural Engineers Associations can apply for positions on these committees: • Basic Education Committee • Communications Committee • Continuing Education Committee • Structural Engineer Emergency Response Committee • Structural Engineering Summit Committee • Young Members Support Group Committee The application, along with more details, can be found on www.ncsea.com.

NCSEA Webinars May 16, 2017 Structural Welding: Special Inspections with the IBC & AISC Robert E. Shaw, Jr., P.E.

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April 2017

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More detailed information on the webinars and a registration link can be found at www.ncsea.com.

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June 15, 2017 Seismic Design of Large Wood Panelized Roof Diaphragms May 2, 2017 Structural Steel & Bolting: Special Inspections with the IBC & AISC in Heavy Wall Buildings John Lawson, S.E. Robert E. Shaw, Jr., P.E.

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April 18, 2017 Upcoming Changes to AISC 341 – Seismic Provisions for Structural Steel Buildings James O. Malley, S.E.

COUNCI L

The Newsletter of the Structural Engineering Institute of ASCE

Structural Columns

Structures Congress 2018 Call for Abstracts and Sessions CALL FOR PROPOSALS Abstracts and session descriptions are invited addressing topics listed below, with emphasis on presentations that highlight innovative topics with practical application. Additional types of sessions that encourage broader participation and a more dynamic and interactive approach are available. Abstracts & Session Proposals due June 5, 2017 Submit your sessions at www.structurescongress.org.

Abstracts Single Abstracts address a single subject. These are reviewed and grouped with other single abstracts to create a full session, but may also be used in other session types described above. Part of the submission process includes telling NTPC how this abstract/session impacts and improves the Structural Engineering profession. Think about how this can help create leaders in the Structural Engineering Profession. How does this benefit the profession? What impact does this have globally or socially? How does this bring together the broader project teams? How does this help SEI realize the Vision for the Future of Structural Engineering? Questions? Contact Debbie Smith at dsmith@asce.org or 703-295-6095

Session Types At submission, you must select your first choice of one of these options. • Innovative Executive Sessions (IES) – 10 speakers present for 3 minutes each, each with one PowerPoint slide. Then all move to an area for small group discussion with each presenter. This consists of three 20 minute blocks so the audience can rotate to different speakers. • Comprehensive Sessions – may extend beyond the traditional 90 minute time frame and will provide detailed information as well as practical or technical application. An example of this might be a session on a new Code or Standard. Audience participation and dividing into small working groups, if appropriate, is encouraged. • Panel Sessions – multidiscipline project team members discuss project’s success and lessons learned, etc. Panel sessions can also include debates or other formats. • Case Studies – presenter(s) describe in detail an entire project including issues like management structure, design, issues encountered, solutions to overcome problems, and outcome. • Other creative sessions – encourage audience participation and even breakout groups • Traditional Sessions – a moderator and 4 to 5 presentations/papers.

Invited Topics Blast & Impact Loading & Response of Structures

Construction & Varied Building Types Damping, Isolation, and Smart Structures Extreme Load Issues (fire, seismic, flood) Disproportionate Collapse Foundations and Substructures How Buildings & Codes can Address Underserved Populations & Congestion Resilience and Sustainability Restoration and Repair of Existing Structures Seismic Retrofitting Structural Innovations – Materials, Analysis or Design

Blast and Impact Load Characterization Computational Methods Nonstructural Components Post Blast Issues Progressive Collapse Risk Assessment Robustness/Resilience/Redundancy of Structures Special Structures Structural Engineer as Innovator in Terrorism Protection

Business and Professional Practice

Bridges and Transportation Structures Analysis and Material Issues Bridge Design Practice, Code & Standards Bridges as Solutions to Societies Transportation Issues Construction & Rehabilitation Design & Extreme Loads Foundations and Substructures Inspection, Assessment, and Evaluation Monitoring, Serviceability, and Smart Bridges Resilience and Sustainability

Buildings Codes and Standards – Buildings Connection Detailing and Design Constructability/Erection/Fabrication Issues and Techniques

BIM in Business Practice CASE Spring Risk Management Convocation Engineer’s Role in Leading Social Change Globalization Law and Ethics Licensing and Certification Profession Practice and Engineering Management Professional Practices Lessons Learned Project Delivery Systems Risk Reduction and Claims Management Sharing Claim experiences Trial Designs & Design Examples

Education ABET Accreditation Capstone Projects

STRUCTURE magazine

Educating the Global Engineer Leadership and Professionalism Learning and Education Reform Structural Engineering Curriculum Teamwork and Non-Technical Education

Forensic Accidents and Accident Investigation Methods Collapses and Collapse Investigation Methods Failure Case Studies and Investigation Methods Failures due to Design Errors and Omissions Failures due to Product or Material Defects

Natural Disasters Climate Change Earthquake Hurricane Storm Surge Tornado Tsunami

Nonbuilding and Special Structures Analysis Procedures for Loads other than Seismic Application of Seismic Isolation and Supplemental Damping to Nonbuilding ST Codes and Standards Nonbuilding Design Loads for Nonbuilding Structures and Special Structures Performance & Loading of Nonbuilding Structures in Past Earthquakes Practical Design and Detailing

April 2017

Nonstructural Systems and Components Analysis Procedures for Loads other than Seismic Ceiling Systems, Curtain Walls, and Cladding Codes and Standards – Nonstructural Systems Design Loads for Nonstructural Systems and Components Equipment Anchorage and Design Mechanical, Electrical, and Plumbing Systems Performance of Nonstructural Components in Past Earthquakes Practical Design and Detailing Seismic Qualification of Equipment to Meet ASCE 7-10 Certification

Research Computational Methods of Analysis Hybrid Simulation New Research Novel Structural Materials Resilience Risk and Reliability Analysis Structural Control Structural Health Monitoring Structural Optimization Methodology & Applications Structural Testing

ASCE is proud to announce the release of Dream Big: Engineering Our World. This film, celebrating how engineering builds our world, was championed by ASCE with strong support from Bechtel Corporation. Narrated by Academy Award® winner Jeff Bridges, Dream Big: Engineering Our World is a first of its kind film for IMAX and giant screen theaters that will transform how we think about engineering. From the Great Wall of China and the world’s tallest buildings to underwater robots, solar cars, and smart, sustainable cities, Dream Big celebrates the human ingenuity behind engineering marvels big and small, and reveals the heart that drives engineers to create better lives for people around the world. This film will take viewers on a journey of discovery from the world’s tallest building to a bridge higher than the clouds. Along the way, the audience will witness how today’s engineers are shaping the world of tomorrow. Dream Big is more than a movie, it’s a movement.

Structures Congress 2017 The Premiere Event for Structural Engineering Come for the innovative solutions and cutting-edge knowledge, leave with connections and resources to advance your career. Visit the congress website at www.structurescongress.org for more information and to register

Errata SEI posts up-to-date errata information for our publications at www.asce.org/SEI. Click on “Publications” on our menu, and select “Errata.” If you have any errata that you would like to submit, please email it to Jon Esslinger at jesslinger@asce.org.

SEI Local Activities Austin Chapter The SEI Austin Chapter held its second Structural Engineering Talks event, March 9, at the Alamo Drafthouse in Austin, TX. Industry and academic leaders, Gregory Fenves, Stan Caldwell, William Bulleit, and Kirk Marchand, presented talks on a broad range of topics. Learn more on the Chapter website at https://sites.google.com/site/austintxsei.

Illinois Chapter The SEI Illinois Chapter will be presenting its 22nd Biennial Lecture Series in March and April. These prestigious seminars feature distinguished speakers from across the globe and attract many talented professionals from the local area. Learn more on the Chapter website at www.isasce.org/technical-groups/ structural-engineering-institute-illinois-chapter-sei-il.

Welcome to the SEI Norfolk Chapter The new SEI Norfolk Chapter is planning to hold technical presentations on innovative structural designs, some as joint events with AIA, ULI, and AGC, to further integrate structural STRUCTURE magazine

engineers in the forefront of project development. Chapter activities will also include site tours, sessions designed to help study for and pass the SE Exam and volunteering at ASCE Norfolk Branch events. To learn more, contact SEI Norfolk Chapter Chair Chris Vaught at chris.vaught@mbakerintl.com.

Get Involved in Local SEI Activities Join your local SEI Chapter, Graduate Student Chapter (GSC), or Structural Technical Groups (STG) to connect with colleagues, take advantage of local opportunities for lifelong learning, and advance structural engineering in your area. If there is not a SEI Chapter, GSC, or STG in your area, review the simple steps to form a SEI Chapter at www.asce.org/structural-engineering/sei-local-groups. Local Chapters serve member technical and professional needs. SEI GSCs prepare students for a successful career transition. SEI supports Chapters with opportunities to learn about new initiatives and best practices, and network with other leaders – including annual funded SEI Local Leader Conference, technical tour, and training. SEI Chapters receive Chapter logo/ branding, complimentary webinar, and more.

April 2017

The Newsletter of the Structural Engineering Institute of ASCE

Today’s young dreamers will engineer tomorrow’s future – what better time to start dreaming BIG? The Dream Big project encompasses resources and programs designed for students, teachers, engineers, and science centers, including 50+ handson activities, girl-centered events, lesson plans, design challenge exhibits, videos, and more. Visit the Dream Big website at www.dreambigfilm.com to find an IMAX theater near you showing the film, to learn more about the projects featured in the film, view video clips, and find education resources.

Registration Now Open

Structural Columns

Dream Big IMAX ® Film

The Newsletter of the Council of American Structural Engineers

CASE in Point

CASE Winter Planning Meeting Update On February 17 – 18, the CASE Winter Planning Meeting took place in San Diego, CA. CASE does two planning meetings a year to allow their committees to meet face-to-face and interact across all CASE activities. Over 30 CASE committee members and guests were in attendance, making this another well attended and productive meeting. During the meeting, break-out sessions were held by the CASE Contracts, Guidelines, Membership, Toolkit, and Programs & Communications Committees. Current initiatives include: Contracts Committee – Ed Schweiter (ews@ssastructural.com) • Created a Contract Guide for instructing people on the appropriate contract for certain scenarios. • Preparing all CASE Contracts for next legal review in 2018 – prep work has begun with a single clause template being implemented for all sample contract documents. Guidelines Committee – Kirk Haverland (khaverland@larsonengr.com) • Revising the following Practice Guideline Documents: • CASE 962B – National Practice Guidelines for Specialty Structural Engineers • CASE 962-F – A Guideline Addressing the Bidding and Construction Administration Phases for the Structural Engineer • Working on the following new documents: • Commentary on ASCE-7 Wind Design Provisions • Commentary on ASCE-7 Seismic Design Provisions • Began preliminary discussion on a potential Geotech Guideline document/white paper • Future publications: • Guideline on the Use of Geotechnical Reports • White paper on Beyond the Building Code

CASE Member Firms Win Engineering Excellence Grand, Honor Awards

Looking for Innovative Ideas!

Congratulations go out to CASE Member firm Magnusson Klemenic Associates, Inc. for winning a Grand Award. Their highlighted project, Elliott Bay Sewall Habitat and Public Space in Seattle, WA, is a finalist for the Grand Conceptor Award being presented at the 50th Anniversary Engineering Excellence Awards Gala held during the ACEC Annual Convention. CASE Member Firms Thornton Tomasetti & GRAEF won Honor Awards for their respective projects, U.S. Bank Stadium, Minneapolis, MN; NSMJAWA 90-inch Water Main Hot Tap & Line Plug, Des Plaines, IL. STRUCTURE magazine

• Creating a Master Glossary of terms, pulling together all definitions from all publications into one document • Will be reviewing the new AISC COSP and updating the CASE Commentary document with new information • Will be reviewing the 2015 version of Special Inspections and updating the CASE document accordingly Membership Committee – Stacy Bartoletti (sbartoletti@degenkolb.com) • Asking all CASE firms to send in names to populate our online Members-Only Community page. This will help to disseminate CASE news quickly to a wider audience. • Sending recruiting letters to new ACEC firms that have been tagged as having a structural component • Working on retention plan with ACEC staff for upcoming membership renewal period beginning mid-June Programs and Communications Committee – Nils Ericson (nericson@m2structural.com) • Confirmed the session for the 2017 NASCC Steel Conference • Confirmed sessions for the Summer Risk Management Seminar in August • Discussed options for sessions at the 2017 ACEC Fall Conference • Discussed options for the four sessions at the 2018 Structures Congress Toolkit Committee – Brent White (brentw@arwengineers.com) • Tool 1.3 Office Policy Guide template to be released in Spring • Future Tools discussed include: Project Manager Training; Short-term Staffing; Multidisciplinary project; Working with Guidelines Committee on a document related to Delegated Design

Does your firm have an innovative idea or method of practice? Looking to get more involved in short duration projects? We are inviting you to “share the wealth” and submit a proposal for a web seminar topic, publication, or education session you would like to see CASE present at an upcoming conference. Our forms are easy to use, and you may submit your information via email. Go to www.acec.org/coalitions and click on the icon for Idea Sharing to get started. Questions? Contact us at 202-682-4332 or email Katie Goodman at kgoodman@acec.org. We look forward to helping you put your best ideas in front of eager new faces!

April 2017

Once again, CASE will put on the industry’s only seminar dedicated solely to improving your firm’s business practices and risk management strategies. Come and join us and learn about Lessons Learned in Managing Your Risk in Chicago on August 3 – 4. Gather for training and collaboration with industry leaders and project managers from firms of all sizes intended to improve your structural engineering practice. Immerse yourself in topics designed to help engineers learn better ways of reducing areas of risk and liability on projects while learning about tools that are available to implement better practices immediately in your firm. The Seminar is geared towards Owners, Principals, Project Managers, and Risk Managers – if you are concerned with risk management, new trends, and profitability, you cannot afford to miss this event! Registration for the event will open mid-April, seats will be limited. For more information about this seminar, contact Heather Talbert at htalbert@acec.org or 202-682-4377.

Engineers are often asked to serve as expert witnesses in legal proceedings – but only the prepared and prudent engineer should take on these potentially lucrative assignments. If asked, would you be ready to say yes? Developed exclusively for engineers, architects, and surveyors, this unique course will show you how to prepare for and successfully provide expert testimony for discovery, depositions, the witness stand, and related legal proceedings. Applying Expertise as an Engineering Expert Witness is a focused and engaging 1½ day course that will run you through each step of the qualifications, ramifications, and expectations of serving as an expert witness. For more information about the course, please contact Katie Goodman at 202-682-4377 or kgoodman@acec.org.

August 3 – 4, 2017; Chicago, IL

June 15 – 16, 2017; Boston, MA

CASE Risk Management Tools Available Foundation 4: Communication – Communicate to Match Expectations with Perceptions • A high percentage of claims occur because of poor communication. • Be proactive in communications, not reactive. • Create an atmosphere for good and open communication. • If in doubt, communicate early and often. • Select the best method of communication (email may not always be the best approach). • Communicate effectively.

Tool 4-3: Sample Correspondence Guidelines (Updated in 2015!) The intent of CASE Tool 4-3, Sample Correspondence Guidelines, is to make it faster and easier to access correspondence with appropriate verbiage addressing some commonly encountered situations that can increase your risk. The sample correspondence contained within this tool is intended to be sent to the Client, Owner, Sub-consultant, Building Official, Employee, etc., to keep them informed about a certain facet of a project or their employment.

Tool 4-1: Status Template Report This tool provides an organized plan for keeping clients informed and happy. This project status report is intended to be sent to your Client, the Owner, and any other stakeholder you would like to keep informed about the project status.

Tool 4-4: Phone Conversation Log Poor communication is frequently listed among the top reasons for lawsuits and claims. It is the intent of this tool to make it faster and easier to record and document phone conversations.

Tool 4-2: Project Kick-Off Meeting Agenda Effective communication is one of the keys to successful risk management. We often place a significant amount of effort and care into communication with our clients, owners, and external stakeholders. With all that effort, it’s easy to take for granted communication with our internal stakeholders – the structural design team. If a project is not started correctly, there is a good chance that the project will not be executed correctly either. Tool 4-2 is intended to help the Structural Engineer communicate the information that is vital to the success of the structural design team, and start the project off correctly. STRUCTURE magazine

Tool 4-5: Project Communication Matrix This tool is to provide an easy to use and efficient way to (1) establish and maintain project-specific communication standards, and (2) document key project-specific deadlines and program/coordination decisions that can be communicated to a client or team member for verification. You can purchase these and the other Risk Management Tools at www.acec.org/bookstore.

Follow ACEC Coalitions on Twitter – @ACECCoalitions. 61

April 2017

CASE is a part of the American Council of Engineering Companies

Applying Expertise as an Engineering Expert Witness SAVE the DATE!

CASE in Point

First Annual CASE Risk Management Seminar PLAN TO ATTEND!

EnginEErEd Wood Products guidE a definitive listing of wood product manufacturers and their product lines American Wood Council

Phone: 202-463-2766 Email: info@awc.org Web: www.awc.org Product: National Design Specification (NDS) Description: ANSI/AWC NDS-2015 National Design Specification (NDS) for Wood Construction is referenced in the 2015 International Building Code. It includes design information for glulam, I-joists, structural composite lumber, wood structural panels, and cross laminated timber.

Applied Science International, LLC

Phone: 919-645-4090 Email: support@appliedscienceint.com Web: www.extremeloading.com Product: Extreme Loading for Structures Description: A new level of nonlinear dynamic structural analysis. Efficiently study structural failure from any number of actual or possible extreme events. Model timber structures for progressive collapse, blast, and seismic analysis. Model high-rise structures composed of reinforced concrete, steel composite and more with as-built and as-damaged details.

Dlubal Software, Inc.

PFS TECO

Phone: 608-839-1013 Email: steve.winistorfer@pfsteco.com Web: www.pfsteco.com Product: Certification, inspection, and testing services for EWP manufacturers Description: Employee-owned, independent, third-party certification and testing agency for manufacturers of panel products, engineered wood products, building components, and hearth products; an approved IPIA/DAPIA for HUDcode manufactured housing. Five U.S. offices, two laboratories and clients in more than a dozen countries. PFS TECO – Marks You Can Build On!

RISA Technologies

Phone: 949-951-5815 Email: info@risa.com Web: risa.com Product: RISAFloor Description: RISAFloor and RISA-3D form the premiere software package for wood design. Create 3D models of your entire structure and get full design of wood walls (with and without openings), flexible wood diaphragms, dimension lumber, glulams, parallams, LVL’s, joists and more. Custom databases for species, hold-downs and panel nailing offer total flexibility.

Phone: 267-702-2815 Email: info-us@dlubal.com Web: www.dlubal.com Product: RFEM Description: RF-Limits now has design of timber connections with steel plates per NDS-2015. RFTimber AWC is complete with LRFD/ASD design of members according to NDS-2015, including fire resistance design, tapered/curved glulam design, and automatic cross-section optimization. With RF-Laminate, deflection and stress design of crosslaminated timber (CLT) is possible per NDS-2015.

S-FRAME Software

Hoover Treated Wood Products, Inc.

Simpson Strong-Tie ®

Phone: 800-531-5558 Email: pam@plywall.com Web: www.plywall.com Product: PLYWALL® Pre-Engineered Noise Barrier Description: Pre-engineered, pre-fabricated treated wood barrier system used for noise abatement and aesthetic screening. PLYWALL® has been tested in accordance with ASTM E-90 with performance and STC ratings comparable to concrete and masonry. Heights range from 6-32 feet and can meet the news IBC Codes for wind loading.

LifeSpan Decks

Phone: 919-845-1025 Email: swalden@steelnetwork.com Web: www.lifespandecks.com Product: Lifespan Steel Framed Decks Description: Different than wood framed decks that deteriorate over a short period of time, Lifespan Steel Framed Decks will last a lifetime. Options for concrete topped deck, composite topped deck, and overhead garage storage

Phone: 604-273-7737 Email: info@s-frame.com Web: s-frame.com Product: S-LINE Description: Continuous Concrete Beam Design and Detailing with S-LINE. Design and detail reinforced concrete beams for both strength and serviceability to multiple codes. View interactive results including capacity envelopes on shear, moment, and torsion diagrams. Comprehensive reports incorporate equations employed, clause references, and diagrams.

Phone: 800-925-5099 Email: web@strongtie.com Web: www.strongtie.com Product: LSSJ Field-Adjustable Jack Hanger Description: The ideal hanger for connecting jack rafters to hip/valley members. Its simple design makes installation intuitive and quick, resulting in lower labor costs. Featuring a versatile, hinged seat, the LSSJ is easily field-adjustable to typical rafter slopes. Product: Strong-Wall® Wood Shearwall Description: Offers added front, back and side access holdowns and top-of-wall connection that allow for easy installation and inspection in various framing conditions. The Strong-Wall Wood Shearwall delivers greater lateral-force-resistance performance than most comparable wood shearwalls while providing installers the ability to field-trim the shearwall.

StructurePoint

Phone: 847-966-4357 Email: info@StructurePoint.org Web: www.structurepoint.org Product: Reinforced Concrete Design Software Description: spSlab is used for analysis, design and investigation of reinforced concrete floor systems; analyzes beams, one-way slab systems (including standard and wide module joist systems), and two-way slab systems (including waffle and slab bands). spColumn is used for design of shear walls, bridge piers as well as typical framing elements in buildings and structures.

Trimble Solutions USA, Inc.

Phone: 770-426-5105 Email: Kristine.plemmons@trimble.com Web: www.tekla.com Product: Tekla Structures Description: Can be used for wood framing: True BIM model of wood framing, parametric components allow for easy creation and design change, easily add or move doors and windows, library of industry standard wood connections included, clash checking functionality to eliminate change orders, easily customizable. Product: Tedds Description: Design a range of wood elements, including: beams (single span, multi-span and cantilever); wood columns; sawn lumber, engineered wood, glulam and flitch options; shear walls (multiple openings; segmented or perforated); connections (bolted, screwed, nailed, wood/wood and wood/steel); produce detailed and transparent documentation.

TrimJoist Corporation

Phone: 800-844-8281 Email: marty.hawkins@trimjoist.com Web: www.trimjoist.com Product: TrimJoist Description: Combination of an open web floor truss and a wood I-joist bringing the best features of each together to form a trimmable floor truss. As the name indicates, it can be trimmed on the construction site for a perfect fit. TrimJoist is produced in stock lengths from 4 feet to 30 feet and in depths of 117/8-, 14- 16and 18-inch.

WoodWorks Software

Phone: 800-844-1275 Email: sales@woodworks-software.com Web: www.woodworks-software.com Product: WoodWorks Design Office Suite Description: Version 11 now available: NDS 2015, IBC 2015, SDPWS 2015 & ASCE 7-10 compliant. SHEARWALLS: designs perforated and segmented shearwalls; generates loads; rigid and flexible diaphragm distribution methods. SIZER: designs beams, columns, studs, joists; up to 6 stories. CONNECTIONS: Wood-to-wood, -steel, -concrete.

All Resource Guide forms for 2017 are now available on the website, visit www.STRUCTUREmag.org.

STRUCTURE magazine

April 2017

Work quickly. Work simply. Work accurately. StructurePoint’s Productivity Suite of powerful software tools for reinforced concrete analysis & design

Finite element analysis & design of reinforced, precast ICF & tilt-up concrete walls

Analysis, design & investigation of reinforced concrete beams & one-way slab systems

Design & investigation of rectangular, round & irregularly shaped concrete column sections

Analysis, design & investigation of reinforced concrete beams & slab systems

Finite element analysis & design of reinforced concrete foundations, combined footings or slabs on grade

StructurePoint’s suite of productivity tools are so easy to learn and simple to use that you’ll be able to start saving time and money almost immediately. And when you use StructurePoint software, you’re also taking advantage of the Portland Cement Association’s more than 90 years of experience, expertise, and technical support in concrete design and construction.

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Visit StructurePoint.org to download your trial copy of our software products. For more information on licensing and pricing options please call 847.966.4357 or e-mail info@StructurePoint.org.

STRUCTURE magazine | April 2017

Articles inside

BUILDING BLOCKS

STRUCTURAL SYSTEMS

INSIGHTS

CONSTRUCTION ISSUES

EDITORIAL

HISTORIC STRUCTURES

STRUCTURAL SUSTAINABILITY

STRUCTURAL REHABILITATION

STRUCTURAL SPECIFICATIONS