STRUCTURE magazine - February 2020

STRUCTURE FEBRUARY 2020

NCSEA | CASE | SEI

STEEL/CFS

INSIDE: The Key at 12th

26

2020 Aluminum Design Manual Hotel Julian Hale Centre Theatre

9 22 30

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It was brought to our attention that a photo was inadvertently omitted of Michael Gustafson, P.E., one of the speakers for the Closing Keynote at the SEI Structures Congress (January 2020, page 46). STRUCTURE apologies for this oversight.

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STRUCTURE magazine is always looking for Structural Forum (opinion) articles and Letters to the Editor. We preserve a page at the end of the magazine to print these types of articles, as space permits. Please send your pieces to publisher@structuremag.org.

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by The National Council of Structural Engineers Associations (a nonprofit Association), 20 N. Wacker Drive, Suite 750, Chicago, IL 60606 312.649.4600. Application to Mail at Periodicals Postage Prices is Pending at Chicago, IL and additional mailing offices. STRUCTURE magazine, Volume 27, Number 2, © 2020 by The National Council of Structural Engineers Associations, all rights reserved. Subscription services, back issues and subscription information tel: 312-649-4600, or write to STRUCTURE magazine Circulation, 20 N. Wacker Drive, Suite 750, Chicago, IL 60606.The publication is distributed to members of The National Council of Structural Engineers Associations through a resolution to its bylaws, and to members of CASE and SEI paid by each organization as nominal price subscription for its members as a benefit of their membership.

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Contents FEBRUARY 2020

Columns and Departments 7

Editorial New Vision and Mission Guide NCSEA’s Direction in 2020 and Beyond

By Susan Jorgensen, P.E., SECB

9

Structural Specifications The 2020 Aluminum Design Manual

By J. Randolph Kissell, P.E., and Ronald D. Ziemian, Ph.D., P.E.

12

Structural Licensure Significant Structures

By Kristin Killgore, P.E., S.E.

14

Structural Rehabilitation Evaluation of Existing Timber Structures

By Jim DeStefano, P.E., AIA

19

Norwalk Bridge Disaster

Cover Feature 26 THE KEY AT 12TH

By Peter W. Somers, P.E., S.E.

By Frank Griggs, Jr., D.Eng., P.E.

32

By Ciro Cuono, P.E.

building, the Key Systems Building. This is a textbook example of how the 42

By David Nickell, S.E., Martin White, S.E., and Roger Reckers, S.E.

The project goal was to transform an abandoned property into a boutique hotel – Hotel Julian – including six new levels and rehabilitation of a once-prominent structure in the heart of Chicago’s downtown that had fallen into disrepair.

30 HALE CENTRE THEATRE

Structural Forum Operational, Redundancy, and Ductility Factors for Bridge Structures

Features 22 RISING ABOVE

InSights Design-Build and the Structural Engineer

Engineers created a new structure that integrated an adjacent historic AEC industry can meld modern design with classic architecture.

Historic Structures

By Roumen V. Mladjov, S.E., P.E.

In Every Issue 4 13 35 36 38 40

Advertiser Index Noteworthy Resource Guide – Bridge NCSEA News SEI Update CASE in Point

By Tait A. Ketcham, S.E., and Darren G. Dickson, S.E.

The Hale Centre Theatre is a world-class theater experience that is truly unique, and

On the Cover

was a structural engineering challenge to incorporate the stage and crane system

Courtesy of STRUCTURE’s Editorial Chair, John A.

technologies into the design.

The Key at 12th, Oakland, CA.

Dal Pino, S.E. Read more on page 26.

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

FEBRUARY 2020

5

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EDITORIAL New Vision and Mission Guide NCSEA’s Direction in 2020 and Beyond

By Susan Jorgensen, P.E., SECB, F.SEI, F.ASCE

I

t is an honor to address you as the 2020 President of the National engineers, what more can we be doing to encourage young people Council of Structural Engineers Associations (NCSEA). This is to join our profession? For one thing, the NCSEA Young Member going to be an exhilarating year as we follow through with some Group Support Committee has done a great job of developing tools significant changes. We are hosting the first-ever SEA Leadership to help advocate for structural engineering. I encourage you to log Retreat in May, bringing together the leaders of the organization. We onto the Member Portal for access to these documents. have changed our fiscal year to run from April 1st to March 31st. And, The NCSEA Structural Engineering Engagement and Equity (SE3) the Board of Directors is looking forward to further coordination Committee has also done a great job of gathering information on the and cooperation with our counterparts at the Structural Engineering current state of our profession. Its surveys of structural engineers from Institute (SEI) of the American Society of Civil Engineers (ASCE) across the country include overall career satisfaction and retention, and the Council of American Structural Engineers (CASE) of the career development, pay, and work/life balance. The findings help us American Council of Engineering Companies (ACEC). understand opportunities to enhance our profession. I look forward As announced at the NCSEA Structural Engineering Summit on to the SE3 Committee being able to use this information to help November 13, a group of leaders in the organization worked together develop tools and guidelines for how we can encourage engagement, in 2019 to develop a new strategic plan for the organization. The equity, and diversity. new vision statement, which describes our Advocacy includes educating the public desired future state, is, “Structural engiabout the value that structural engineers neers are valued for their contributions provide to society. To do this, we need to A strategic plan is only to safe structures and resilient combe able to step up and be leaders, not just of munities.” The new mission statement, our firms, but in the community. As most valuable if there is followwhich articulates the organization’s role in of you know, I have been a vocal advocate achieving the Vision, is “NCSEA, in partthrough. It does not do any of structural engineering licensure for a nership with its Member Organizations, very long time. NCSEA plans to develop supports practicing structural engineers tools that its Member Organizations and good to go to all this effort to be highly qualified professionals and individual engineers can use within their successful leaders.” To achieve this, the communities to demonstrate the value that if we just put the resulting group developed four goal statements we can bring. and supporting strategies that will be the In December, NCSEA conducted a webidocument on the shelf. guidelines for NCSEA’s direction for the nar providing details on the strategic plan, foreseeable future. presented by members of the Board of The goals fall into three categories: Education and Training, Perception Directors. If you were not able to join that webinar, I encourage you and Professionalism, and Codes and Standards. There are two distinct to watch the recorded version at https://bit.ly/2FvU8tr. There are also goals under Perception and Professionalism: Advocacy (External several documents mentioned in the webinar that are available for downCommunication) and Collaboration (Internal Communication). The load from the member-only pages. If you have questions, reach out to NCSEA Communications Committee, which was reorganized a few one of the Board members; for example, your Member Organization’s years ago, will have a big hand in helping us achieve these last two designated liaison (www.ncsea.com/members/organizations). goals, which are the ones that I am most excited about.

What is next? A strategic plan is only valuable if there is followWhen I was growing up, my mother worked for the Bureau of through. It does not do any good to go to all this effort if we just Reclamation, so I was introduced to the civil engineering profession. put the resulting document on the shelf. At its January meeting, My uncle and a close family acquaintance had attended the South the primary agenda item for the NCSEA Board of Directors was Dakota School of Mines and Technology, so I was familiar with their to determine which initiatives will be our focus for 2020. These are programs. I also had a great deal of encouragement from family and actionable, measurable tasks that we can strive to accomplish within friends. Unfortunately, not all potential engineers are as lucky. Many the next year or two. engineers seem to think that future engineers will come from STEM I am looking forward to getting started and further advancprograms and will be the best and brightest of the class. While this ing this organization.■ will be true, there will be others who could become outstanding engineers who may not have the encouragement and support to be Susan Jorgensen is the Quality Control Manager for Studio NYL, a structural steered toward engineering. engineering and façade design firm in Boulder, CO, and a Senior Structural We spend much time focusing on how young women are not being Engineer for Integral Engineering, a woman-owned small-business structural encouraged to pursue engineering, but, as my husband points out – design firm in Centennial, CO. She is currently the President of the NCSEA Steve is both a professional geologist and a professional engineer – these Board of Directors. (susiejorg315@comcast.net) same efforts need to be directed to young men as well. As structural STRUCTURE magazine

F E B R U A R Y 2 02 0

7

structural SPECIFICATIONS The 2020 Aluminum Design Manual Spoiler Alert!

By J. Randolph Kissell, P.E., and Ronald D. Ziemian, Ph.D., P.E.

T

he next edition of the Aluminum Association’s Aluminum Design Manual (ADM) became available in January 2020 (Figure 1).

Updated every five years, the Manual includes the Specification for Aluminum Structures which provides for allowable strength and load and resistance factor design of aluminum structures, members, and connections. Because compliance with this Specification is required by the International Building Code (IBC), changes to the Specification directly affect most building applications of aluminum in the United States. Furthermore, the Specification’s provisions are used by other code organizations, such as the American Welding Society (AWS) and the American Association of State Highway and Transportation Officials (AASHTO) in their standards for aluminum structures. This article reviews the significant changes to the Specification as compared to the 2015 edition.

The ADM was first published in 1994 but was preceded by several Aluminum Association publications dating back to the 1960s, including the Specification for Aluminum Structures, which celebrated its 50th anniversary in 2017. The Specification was reorganized in 2010 so that its presentation was consistent with the AISC Specification for Structural Steel Buildings. This format, which has been retained in the 2015 and 2020 editions, is presented as a unified specification that provides nominal strengths for use in both the allowable strength design (ASD) and load and resistance factor design (LRFD) methods.

It is organized into chapters and appendices that are consistent with AISC’s topics; for example, Chapter D addresses members in axial tension, and Chapter E addresses members in axial compression.

Welded Strengths Aluminum alloys are strengthened by tempering, which is achieved by heat treatment or cold working. The heat of welding offsets the increased strength gained by tempering, and this strength reduction zone typically extends 1 inch (25 mm) in each direction from the centerline of a weld. For welded connections, designers need to know the weld-affected tensile ultimate strength. Both the weld-affected tensile ultimate strength and the weld-affected tensile yield strength are required to design welded built-up members. Furthermore, the base metal and filler metal alloys in a weldment often differ and, consequently, the weld-affected strengths of both are needed.

While minimum weldaffected tensile ultimate strengths are provided in the American Welding Society’s D1.2 Aluminum Figure 1. The 2020 Aluminum Design Manual.

Welding Code for base

Table of nominal strengths of aluminum filler metals.

Filler

Tensile Ultimate Strength Ftuw (ksi)

Tensile Yield Strength Ftyw (ksi)

1100

11

3.5

2319

35

26

4043

24

11

5183

40

18

5356

35

14

5554

31

12

5556

42

19

5654

30

11

metal alloys, no strengths are established for aluminum filler metals in AWS’s specifications or codes. Consequently, accurately establishing the welded strengths needed for design in the Specification has been an ongoing effort. The 2020 Specification is the first to establish the weld-affected tensile ultimate and tensile yield strengths of both the base metals and the filler metals that are addressed by the Specification.

The strength of the weld-affected zone, which includes both base metal and filler metal, is the weighted average of the strengths of the base metal and the filler metal defined by their contribution to the cross-sectional area of the weld-affected zone. The filler metal strengths given in the 2020 Specification are shown in the Table.

Because welding reduces the strength of heat-treated or coldworked aluminum, designers sometimes seek to regain strength by post-weld heat treatments. An example is an aluminum light pole with a welded base; the base weld weakens the assembly where the maximum moment from wind loads occur. Designs utilizing post-weld heat treatments have been limited, however, because the previous Specification only provided post-weld heat-treated strengths for 6005 and 6063 alloys. The 2020 update adds the post-weld heat-treated strengths for 6005A and 6061, significantly extending the Specification’s usefulness.

Screw Chases Perhaps the most compelling reason to use aluminum in structural applications is that it can be cost-effectively extruded, producing complex cross-sections without labor-intensive fabrication. A good example is shown in Figure 2, where a chase is provided at the top of the extrusion to receive a screw anywhere along the extrusion’s length, a detail widely used in architectural applications.

While screw chases provide economical connections for aluminum members, the pull-out strength of fasteners in the chase has not been addressed in structural design standards. The 2020 Specification is the first to include a pull-out strength for screws in screw chases, which for ¼-inch-diameter fasteners is given as: FEBRUARY 2020

9

Rn = (0.021 in2)Le Ftu (14/n)2/wc , where Le = length of engagement of the screw’s threads in the depth of the chase (inches) Ftu = tensile ultimate strength of the screw chase extrusion (k/in2) n = number of threads/inch of the screw wc = nominal width of the chase (inches) To determine the available pull-out strength (φRn for LRFD and Rn /Ω for ASD), φ = 0.50 and Ω = 3.0.

Flexural Strength Several changes are made to the flexural strength provisions in Chapter F.

compression or the elements in flexural compression, and computing the section modulus of each group. The 2020 Specification simplifies this by providing equations to use the elastic buckling stress of the shape to determine the local flexural buckling stress of the shape directly.

Single Angles The flexural strength of single angles is revised, consistent with changes for single angles in the 2016 AISC Specification.

Block Shear Strength

The block shear strength provision in previous Specification editions was similar to an earlier AISC The equation for the bending coefficient, Cb, approach in which the strength was the lesser of which accounts for the variation in the moment yielding on the gross shear area with rupture on over the unbraced length of a beam in deterthe net tensile area and yielding on the gross tensile mining the lateral-torsional buckling strength, area with rupture on the net shear area. In the 2020 Figure 2. Extruded aluminum screw chase. is changed to: Specification, the block shear strength is now taken as the shear rupture strength on the average of the 4Mmax net and gross shear areas plus the tensile rupture strength on the net R ≤ 3.0, where Cb = m 2 √Mmax + 4MA2 + 7MB2 + 4MC2 tensile area. The revised strength is more accurate and less cumbersome Mmax = absolute value of the maximum moment in the to compute. unbraced segment MA = moment at the quarter-point of the unbraced segment Flanges and Webs with Concentrated Forces MB = moment at the midpoint of the unbraced segment MC = moment at the three-quarter-point of the unbraced Web crippling was the only case of concentrated forces on flanges or webs segment addressed in previous editions of the Specification for Aluminum Structures.

Rm = 1.0 except for unbraced lengths of singly-symmetric In the 2020 Specification, the web crippling strength for extruded shapes members subjected to double-curvature bending from (Figure 3) is revised and made less conservative, and flange local bendtransverse loading, ing and web local yielding are added. The strengths for these three cases 2 are similar to those in the 2016 AISC steel Specification, as the rationale Iyf Rm = 0.5 + 2 for these strengths can be equally applied to both aluminum and steel.

Iy

Bending Coefficient

( )

Iyf =

moment of inertia of the flange on the negative side of the midheight (where the direction of the load is the positive direction) about the minor axis of the shape Iy = minor axis moment of inertia of the shape This equation is given in the Structural Stability Research Council’s Guide to Stability Design Criteria for Metal Structures (Wiley, 2010).

Flexure and Axial Compression The Specification includes a direct strength method for determining the capacity of members in flexure or axial compression. This method uses the elastic buckling strength determined by the finite strip method (FSM), which is an eigenvalue analysis of a model of a member divided into strips that extend along the member’s length. The opportunity to employ such a method in design is especially important for aluminum because extruded aluminum shapes can be very intricate, which complicates the determination of their buckling strengths.

The 2015 Specification provided a method to determine a section’s flexural local buckling stress using the section’s elastic buckling stress from FSM. This elastic buckling stress was used to determine the strength of the elements of the section in uniform compression and the strength of the elements of the section in flexural compression. The strengths of the two groups of elements were then combined using a weighted average based on their section moduli.

This approach was rather cumbersome because it required assigning each element of the section to either the elements in uniform 10 STRUCTURE magazine

Bridges and Buildings Around 1960, several aluminum highway bridges were built in the U.S. Consequently, and since its first appearance in 1967, the Specification for Aluminum Structures has addressed both bridges and buildings with a different set of safety factors for each. For example, while the Specification set a safety factor on tensile rupture of 1.95 for buildings, the safety factor for tensile rupture was 2.20 for bridges.

Figure 3. Web crippling of extruded members.

In this regard, the aluminum Specification has differed from its steel counterpart, the AISC Specification for Structural Steel Buildings, which from its beginning in 1923 has addressed building structures only.

When AASHTO developed the first LRFD bridge design specifications in the 1990s, they used the Specification for Aluminum Structures as the source of the nominal strengths for aluminum structural components and established resistance factors for aluminum bridges. Consequently, when the first LRFD Specification for Aluminum Structures was published in 1994, it addressed buildings only and left load and resistance factor design of aluminum highway bridges to AASHTO. However, allowable strength design safety factors for aluminum highway bridges lingered in the Specification for Aluminum Structures, even though allowable strength design is no longer used for bridges. The 2020 Specification drops references to bridges, thus limiting its scope to building structures, defined in the Specification as a structure of the type addressed by a building code. As with the AISC steel Specification, the aluminum Specification may reasonably be applied to all structures designed, fabricated, and erected in a manner similar to buildings, with building-like vertical and lateral load-resisting elements.

The 2026 Aluminum Design Manual Just as the AISC has adopted a six-year cycle for revisions to the steel Specification, the Aluminum Association is considering a six-year interval between revisions to the Aluminum Design Manual. Because the IBC has a three-year revision cycle, a six-year cycle may be more suitable for standards like the Specification for Aluminum Structures

that are referenced by the IBC. This also has the benefit of reducing the frequency of changes to design standards, thereby allowing design professionals to master them better.

In the next revision cycle, several issues may be considered for the aluminum Specification, including: • The flexural and axial compression strengths of members with transverse welds that affect the full cross-section or part of the cross-section • The flexural and axial compression strengths of members with longitudinal welds • An unbraced length below which lateral-torsional buckling does not occur • Provisions for tubular connections Of course, the authors would appreciate learning of any other issues or suggestions for improving future editions of the ADM. The 2020 Aluminum Design Manual is available from the Aluminum Association at www.aluminum.org.■ J. Randolph Kissell is a Managing Consultant for Trinity Consultants. He serves on Aluminum Association, ASTM, Canadian Standards Association, American Welding Society, and American Petroleum Institute committees that address aluminum structures, and teaches ASCE’s aluminum structural design seminar. (rkissell@trinityconsultants.com) Ronald D. Ziemian is a Professor in the Department of Civil and Environmental Engineering at Bucknell University and currently serves on the AISC, AISI, and Aluminum Association specification committees. (ziemian@bucknell.edu)

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11

structural LICENSURE Significant Structures

Suggested Language for Partial Practice Restrictions

By Kristin Killgore, P.E., S.E., PMP

T

he Structural Engineering Licensure Coalition (SELC) consists of representatives from the Council of American Structural Engineers (CASE) of the American Council of Engineering Companies (ACEC), the National Council of Structural Engineers Associations (NCSEA), the Structural Engineering Institute (SEI) of the American Society of Civil Engineers (ASCE), and the Structural Engineering Certification Board (SECB).

SELC has developed a document that provides a model definition for the term “significant structures,” which is used in structural engineering licensure legislation in several states and is being considered by several others to define partial practice restrictions. The national discussion and state-by-state adoption of structural engineering licensure have spurred the need to articulate to the public and Authorities Having Jurisdiction (AHJs) the best practices and industry intent when AHJs work to define partial practice restriction legislation. SELC worked to provide broad guidance with the understanding that each licensing board will be required to judge for itself the definition that best serves its jurisdiction.

The development of professional engineering legislation in the early 1900s established the precedent used by state and local jurisdictions through the ensuing decades to develop laws to protect the public health, safety, and welfare.

The licensing of professional engineers serves as a public statement that individuals practicing engineering meet required standards and seeks to prevent incompetent or unethical persons from practicing. As industry and education advance, so do the needs of the profession to adapt to these new circumstances.

The National Council of Examiners for Engineering and Surveying (NCEES) was formed in 1920 to improve the uniformity of laws and to promote mobility of licensure across state lines. To summarize the NCEES mission, they strive to provide outstanding nationally normed examinations, provide uniform model laws and rules for adoption by the member boards, and to promote professional ethics among all engineers. NCEES provides a platform for state licensing boards to interact with the profession and develop a uniform policy that can be adopted by all states as a standard of competence. Nevertheless, statespecific legislation and rules continue to exist.

12 STRUCTURE magazine

Practicing engineers are forced to navigate each state’s statutes and rules as they apply to their education, examination, and experience.

The history and development of the PE Structural Engineering (SE) exam is a direct response to the need for jurisdictions to distinguish licensed structural engineers from other professional engineers. As a result, professional organizations, such as NCSEA, CASE, ASCE, SEI, and SECB with interest in this topic, collaborate to assist their members with understanding how licensure and legislative policy affects practice. They work to disseminate information to fill the gaps in messaging between the different entities involved.

The NCSEA Structural Licensure Committee has collected the legislative language and policies adopted by each state for the practice of Structural Engineering, either as a licensed SE or PE. They include full practice restriction, partial practice restriction, title restriction, and roster designation. Some states have full practice restriction language that allows only engineers who have passed the NCEES 16-hour PE Structural Engineer exam (SE) to seal structural documents. Other states have a partial practice restriction that stipulates an SE license is required for “significant structures.” The title restriction language defines who can use the title of “Structural Engineer, S.E.” Finally, roster designation is a provision in statutes, rules, or licensing board procedures recognizing every licensee’s discipline, usually based on NCEES examinations passed by the licensee. Roster states keep a public database of all licensed engineers and their assigned disciplines.

Partial practice restriction language stipulates a licensed Professional Engineer with an SE designation is required for designing “significant structures,” and the language differs between jurisdictions. As more states adopt “significant structure” language, SELC has become concerned it is not uniformly defined.

The challenge of establishing a uniform definition of “significant structures” is complicated because different jurisdictions have differing needs. For instance, the high seismic states use partial practice restrictions because they require more sophisticated engineering applications due to increased risks from earthquakes.

Each jurisdiction reviews its needs, risks, and political atmosphere, and then creates policy to protect the built environment. These statutes

and rules generally follow a similar concept and potential application, though their language varies. More states are looking to adopt the NCEES Model Law and Rules, including the credentials for the Model Law Engineer and Model Law Structural Engineer, because they are seeking greater uniformity. Moreover, more applicants are choosing to take the PE Structural exam with a desire to practice across state lines. The shared goal is health, safety, and welfare protection of the public.

The SELC Significant Structure Model Recommendations are intended to be a guideline. SELC worked to represent general conditions that are currently adopted by AHJs and conditions that are being considered by AHJs who have begun the process of implementing structural engineer licensure.

The recommendations cover a wide range of structure types, all of which have specific code requirements and risk implications. The International Building Code (IBC) and ASCE/ SEI 7, Minimum Design Loads and Associated Criteria for Buildings and Other Structures, were the basis in conjunction with various existing statutes and rules. The document addresses both vertical and horizontal structures.

SELC envisions this document being used in multiple ways by AHJs, legislatures, practicing engineers, educators, and students with the general idea of providing a format for uniformity in understanding what a “significant structure” is. A person reading and trying to apply this document to his or her practice can personally decide if gaining the additional credential of S.E. is required. Structural Engineers Associations (SEAs) and other local groups must work with their state licensing boards to review the proposed guidelines and develop rules addressing the relevant needs and challenges by selecting or adapting the specific provisions that best address them.

To review the document, please go to www.selicensure.org.■ Kristin Killgore is an Associate/Project Manager for FSB Architects and Engineers in Oklahoma City. She is the co-chair for the NCSEA Structural Licensure Committee, a representative in the Structural Engineering Licensure Coalition, and a membership committee co-chair of the Oklahoma City Chapter of Commercial Real Estate Women.

FEBRUARY 2020

NOTEWORTHY Marc Barter Honored with Lifetime Achievement Award, NCSEA Media Role Transitioned to Brian Dekker

A

t the 2019 NCSEA Structural Engineering Summit in November in Anaheim, California, Marc Barter, P.E., S.E., SECB, President of Barter and Associates, Inc., Mobile, Alabama, was honored with a Lifetime Achievement Award from NCSEA and STRUCTURE magazine. Marc was recognized during the Awards Celebration for his outstanding vision, tireless dedication, and years Marc Barter, P.E., S.E., SECB of service to STRUCTURE in his role as President of NCSEA Media, the business operations side of the magazine. Marc’s efforts – largely behind the scenes – have been responsible for much of its long-term success, including his wisdom and resolve during the “Great Recession” that ensured its survival at a time when the publishing industry was struggling.

Beyond his involvement with STRUCTURE, Marc has been an integral part of the history of NCSEA. He was one of the Council’s founding members in 1993, subsequently serving on the Board of Directors from 1994 to 2001 and as President in 1999-2000. He also assisted several efforts to start new SEAs around the country as chair of the Member Organization Development Committee. Marc

has previously received two of NCSEA’s Special Awards: the Service Award, which honors those who have made a clear and indisputable contribution to the organization and therefore to the profession; and the Robert Cornforth Award, which is presented to an individual for exceptional dedication and exemplary service to a Member Organization and to the profession.

In January, Marc stepped down from his role as President of NCSEA Media. The NCSEA Media Board of Directors is excited to announce that it has elected another NCSEA Past President – Brian Dekker, P.E., S.E., President of Sound Structures, Inc, Lake Zurich, Illinois – to assume the position going forward. Marc and Brian have been collaborating on this transition for several months. After serving as a member of the Board of Directors of the Structural Brian Dekker, P.E., S.E Engineers Association of Illinois, Brian served on NCSEA’s Board of Directors from 2011 to 2017, including a term as President in 2015-2016. Brian has a passion for outreach and advocacy within the structural engineering profession and his experience as both a volunteer leader and a business owner will be a valuable asset to STRUCTURE’s future.■

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structural REHABILITATION Evaluation of Existing Timber Structures

By Jim DeStefano, P.E., AIA, F.SEI

M

an has been building timber structures throughout Europe and Asia for over 4,000

years. In North America, timber structures have been built since the first Europeans arrived 400 years ago.

Consequently, there are thousands of old timber structures still in service.

When restoring or renovating an old timber structure, or when adapting it to a new use, it is often necessary to evaluate the structural integrity and load-carrying capacity of the timbers. When structural deficiencies are identified, structural remediation

Older timber structures are easily adapted to a variety of uses.

may be in order. If the structural evaluation is based on overly conservative or unrealistic assumptions, the resulting remediation program may be excessively costly and may result in unsightly and unnecessary alterations.

Deterioration and Impairment It is rare to find an old timber structure that does not exhibit some degree of deterioration that may affect the capacity of the structure.

Timber deterioration may be caused by fungal decay, insect infestations, structural overload, or mechanical damage. The reduction in structural load resistance associated with timber deterioration is referred to as impairment.

Fungal decay, often called decay or rot, is by far the most common type of timber deterioration. Rot is caused by a fungus that feeds on the lignin and cellulose fibers of the wood. There are a variety of rot fungi types. Brown rot is the most common form of decay, while wet rot and white rot are not uncommon. Dry rot is a form of brown rot, but the term is frequently misused since many engineers believe all

Wet discolored timber is evidence of decay.

14 STRUCTURE magazine

types of decay are dry rot. Precise identification of fungi is difficult, but, fortunately, it is not necessary for most projects.

Several species of insects bore into or feed on wood tissue. In North America, the most common are termites, powderpost beetles, carpenter ants, and carpenter bees. For purposes of evaluating the structural load-carrying ability of an impaired timber, the portion of the timber containing decay or insect damage is typically treated as a void.

Condition Assessment

The condition assessment of a timber structure begins with a visual examination to evaluate the extent of deterioration and to identify signs of structural distress.

To properly locate the damaged areas in the structure, an understanding of the places where rot is likely to occur is essential.

For example, areas where persistent roof leaks are evident or where timbers are pocketed into a masonry wall are often more susceptible to rot. For a more in-depth evaluation of timber condition, an awl is a simple and indispensable tool for probing the surface of a timber to identify the depth and extent of deterioration, from either An awl is an effective tool for evaluating surface deterioration.

rot or insect damage. Any portion of the techniques is determining what allowwood that can be penetrated with modest able stress values are appropriate. pressure from an awl should be assumed Engineers who are not experienced to be impaired. evaluating timber structures may There may be deterioration present make erroneous assumptions about the within the core of a timber that cannot timber species and grade that can lead be seen and is too deep to probe with to flawed conclusions and misguided an awl. Sounding with a hammer can recommendations. For instance, if for be effective at identifying hidden deteexpediency, Spruce-Pine-Fir (SPF) No. rioration. The sound that the timber 2 grade is assumed for analysis purpose, makes when struck with the hammer but the actual timbers are Southern is an indication of the soundness of the Pine conforming to a Select Structural timber. A dull thud is an indication that grade, the analysis will be overly conserthere may be internal deterioration. vative and will significantly undervalue Some form of nondestructive evalua- A resistance drill can identify hidden deterioration within a timber. the structure. tion (NDE) may be warranted if hidden deterioration is suspected. There are some sophisticated NDE systems Identifying Timber Species and Grade such as ultrasonic stress-wave measurements that have been used with limited success in evaluating deteriorated timbers. Although The timber species must be identified before design values can be not entirely non-destructive, resistance drilling is an effective method determined. Some timber species, particularly hardwood species, have that leaves minimal evidence of the test. distinctive characteristics that can be visually identified by a trained Resistance drilling creates a small diameter hole (typically 1⁄8 inch) eye. However, since timbers in existing structures are often aged, in the timber, and the torque required to advance the drill bit is stained, dirty, or even painted, it is usually necessary to take specimens measured and plotted versus depth. Rotted or insect-damaged areas of the timbers and examine the anatomical features of the wood with clearly show up. a hand lens or under a microscope to determine the wood species.

It is worthwhile to measure the moisture content of the timbers The Forest Products Laboratory provides a wood species identificawith a hand-held moisture meter. A high moisture content (above tion service, but this service is not intended for large quantities of 30%) is an indicator that conditions are conducive to fungal decay. samples or extensive ongoing use by private firms. It is usually more Signs of structural distress such as fractured, split, or deflected timbers should be identified. Particular attention should be paid to connections and joinery since that is where most structural ® failures initiate.

Seasoning checks are not splits and are often misidentified as structural defects. Checks are ordinary timber features and are not defects.

No reduction in design bending strength is warranted for a checked BETTER PERFORMANCE timber. Checks typically do not require remediation.

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In the structural evaluation of an existing timber structure that has been in service for decades, the first step should always be an assessment of the structure’s performance. If the structure is reasonably free from damage or deterioration and has been safely supporting the imposed loads with no sign of structural distress, and no change of use is anticipated that would impose higher loads than have been carried in the past, there is usually no need to embark on a detailed structural analysis or to consider structural remediation.

The National Design Specification for Wood Construction (NDS) is a reliable standard for the structural design of new timber structures but is not a good standard for predicting the actual behavior or adequacy of existing structures. Within timber grade classifications, there is a wide variation in strength properties. The published allowable stress values are calculated based on the weakest 5% of timbers of a given species and grade. Consequently, the published reference design values are very conservative for most of the timbers that are in service.

For adaptive reuse of an old timber structure where the new use has higher loading requirements than the previous use, a structural analysis is appropriate. One challenge when determining the loadcarrying capacity of an existing timber structure using analytical

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expedient to engage the services of a wood not one that has published design values, scientist or a commercial service to identify the design values can be calculated based the species based on small specimens taken on procedures described in ASTM D2555, from the structure.

Standard Practice for Establishing Clear Once the timber species has been identiWood Strength Values, and ASTM D245, fied, the next step is to assign a grade to the Standard Practice for Establishing Structural timber. It would be unusual to find a grade Grades and Related Allowable Properties for stamp on timbers unless the structure is less Visually Graded Lumber. than 50 years old. Published grading rules Allowable stress values should be adjusted are intended for the grading of freshly sawn based on the in-service moisture content timbers at a sawmill. The grading rules have of the timber. The published values in the restrictions on many timber characteristics NDS Supplement are based on timbers that (such as stain, pitch pockets, and pinholes) are in the green condition with a moisture that are primarily of cosmetic concern and content above 19%. Timber gains strength have an insignificant bearing on structural and stiffness as it dries and seasons. Refer to properties. The strength defining timber TFEC (Timber Frame Engineering Council) characteristics are limited primarily to the Technical Bulletin 2018-9 for recommended slope of grain and knot size. Consequently, adjustments to reference design values for when performing in situ grading, greater bending in timbers with a moisture content emphasis should be placed on the slope of of 19% or less. grain and knot size rather than cosmetic Examining the end grain of a timber specimen with a It is essential to base the structural analysis hand lens to identify the wood species. characteristics. on actual timber dimensions rather than In assigning grades to timbers, in-situ grading tabulated nominal dimensions. The timber follows the grading rules of rules-writing agencies such as the Northeast dimensions change as the timbers season and shrink. It is the actual Lumber Manufacturers Association (NeLMA), the Western Wood dimensions that really matter.

Producers Association (WWPA), the Southern Pine Inspection Bureau As one becomes familiar with the imprecision involved in the grad(SPIB), or others. ing rules for timber and the procedures for determining reference Straightness of grain has a significant influence on the flexural or design values in ASTM D245, it becomes clear that, if a timber tensile strength of a timber. A timber with a 1:6 slope of grain has in an existing structure is found to have calculated stresses that approximately 40% of the flexural strength of a timber with a straight exceed the design values given in the NDS Supplement, it does grain. For flexural members, the slope of grain is most critical in regions not necessarily mean that it is not capable of safely supporting the of high bending stress. The slope of grain can safely be permitted to applied loads. It is a mistake to reject a member because calculated exceed grade limits in areas of little or no bending without requiring stresses exceed the design value associated with the given species and that the grade for the entire timber be reduced for determination of grade by relatively small amounts, on the order of 10 percent. For allowable bending stress. example, 50 psi calculated overstress in bending falls more or less Knots are a significant strength-reducing feature in timber due to within roundoff error for that property. Moreover, given that the the deviation of grain around the knot. When grading a timber, knots design value is based on the 5th percentile exclusion limit, flexural located in regions of high flexural strength are of the most interest. stresses that are more than 100 psi above the design value might There is a commonly held belief that old timber is stronger than new reasonably be considered acceptable for timbers in existing structures, timber because the trees grew more slowly in the dense virgin forests particularly if the timbers are performing well. of the old days and “they just do not grow them like they used to.”

While there is some truth to that belief, it is not universally factual.

Conclusion It is generally true for softwood timber species, but it is not true of hardwoods such as oak. Slow grown oak timber is brash (less ductile) If the timber structure is reasonably free from damage or deterioraand weaker than fast grown oak. tion and has been safely supporting the imposed loads with no sign In softwood timber, density often relates to the rate of growth, which of structural distress, and no change of use is anticipated that would is measured as the number of growth rings per inch along the radial impose greater loads than have been carried in the past, service stresses axis. If there are more than six rings per inch measured on a radial exceeding design values need not be reason for strengthening or line and one third or more “summerwood” (this is the less porous replacement of the timber structure. portion of an annual ring of wood that develops late in the growing On the other hand, if timbers are exhibiting signs of structural disseason and is identified as a narrow dark band), Douglas Fir and tress or are severely deteriorated, remedial measures are appropriate.

Southern Pine are graded as “dense.” A “dense” grade designation This article contains excerpts from TFEC 3-2019, Guide to Structural relates to an increased allowable bending strength value in the NDS Evaluation of Existing Timber Structures, published by the Timber of between 15% and 20%.

Frame Engineering Council (TFEC). The full document is available at www.timberframeengineeringcouncil.org.■

Structural Analysis Once the timber species and grade have been established, allowable stress values can be selected from the NDS. If the timber species is

16 STRUCTURE magazine

Jim DeStefano is the President of DeStefano & Chamberlain, Inc., located in Fairfield, Connecticut. (jimd@dcstructural.com)

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historic STRUCTURES Norwalk Bridge Disaster

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

T

his failure was not a structural failure but a failure of safe operational control of a wood and iron swing bridge built across the

Norwalk River for the New York and New Haven Railroad. This line, as the name implies, was built to connect New York City with New Haven, Connecticut. The line was chartered in 1844, but construction did not start until 1847. The first train reached New Haven in January 1849.

After leaving the New York and Harlem Extension at Williamsbridge, the

Bridge Site, approximately 50 miles from New York City. (Note some of the lines were added after the opening of the New York and New Haven line.)

line ran along the north shore of Long Island Sound and had to cross many streams and rivers draining from the mainland into the Sound. Some of these waterways were used for shipping, and the railroad had to provide for the boats using them.

In 1841, the New York and Harlem Railroad built a bridge over the Harlem River for its northern extension, marking the northern boundary of Manhattan Island. It was at Park Avenue (then called Fourth Avenue) with three fixed, wooden, 90-foot-long Town Truss covered spans. The remaining span was a 90-foot wooden swing span with a clearance of about 30 feet on each side of the pivot. The line then headed north to Albany through White Plains, ending at Chatham Four Corners where it linked up with the Albany and West Stockbridge (Boston and Albany) line to Albany. Its engineer was Alan Campbell and his assistant W. W. Evans.

It was decided to build swing bridges, much like the Harlem River span, that, when open, provided for shipping and when closed provided for rail traffic over the navigable rivers the line crossed. The longest of these was at Milford, where it crossed the Housatonic River. The bridge consisted of covered bridges on each end flanking a 134-foot wooden swing bridge. The total length of the bridge was 1,293 feet. The Norwalk Bridge was much shorter but had a similar swing span with open flanking wooden deck trusses. These were not the first wooden swing bridges but were early ones.

Train in the river with some cars still on approach spans, New York City to the right.

The charter for the Norwalk Bridge required a horizontal clearance of 60 feet on both sides of the center swing pier. A tower was placed on the top of the trusses and chains dropped down to the trusses to support the cantilevered arms when the bridge was open. The method used to inform the locomotive engineer as to whether the span was open or closed was a red ball on a high post mounted on the bridge, so it was visible from a distance. “When this is displayed from the top of the pole, it signifies that all is right; but if the engineer can’t see it from a point about a quarter of a mile distant, where there is a sign, on which is written ‘Look out for the Draw’ with a hand pointing in the direction of the ball, he must stop.” This system worked well until May 6, 1853, when a train from New York City, bound for New Haven, ran through the signal and crashed into the Norwalk River with the locomotive, given its speed, actually crashing into the swing span pier 60 feet away.

Local newspapers covered the accident, in part, as follows: “The 8 o’clock train for New York ran off the draw-bridge into the river near this place. One car was completely submerged, and two others completely demolished. There has been a terrible loss of life.

The excitement is so great that it is impossible to get a list of the killed or injured. The engine went through first, followed by two passenger cars. The 4th passenger car split in two, one half of which was thrown into the river and the other half caught on the draw…The drawbridge was open, the steamboat Pacific having just passed through. The locomotive baggage car and two passenger cars plunged into the river, fifteen feet below the surface. Every person in the first two cars were either killed or severely injured…

It appears that the train left New York with about 200 passengers, a number of whom were bound to Bridgeport and other places in Connecticut…The train proceeded as usual until it reached South Norwalk, a distance of about 44 miles from New York. At this place is a bridge across the river, with a draw that swings to one side, leaving an open space for vessels to pass through. It appears that before the train reached Norwalk, the draw had been opened to allow the steamer Pacific to pass through. The steamer had cleared the bridge, but before the draw could be replaced, the train suddenly approached the bridge going at a rate of thirty miles FEBRUARY 2020

19

an hour and perhaps faster. The water at this place, at high tide, is about nine feet deep, and the soft mud beneath it also quite deep.

On a high pole at the draw, a signal is placed, the position of which is, according to the rules of the road, to be arranged by the draw-tender, to indicate that the way is clear or otherwise, as the case may be. It is likewise customary for a man to wave a flag at or near the entrance of the bridge, in the village, to indicate to the engineer that there are no impediments in that immediate locality, as well as to keep people from the track. The engineer alleges that he looked out reasonably and that he not only saw the flag-waving at the point last mentioned but the signal on the pole at the draw so arranged as to indicate that all was right for the train to pass and that he accordingly went on.

Appleton’s illustrations.

The draw-tender, on the other hand, asserts that the reverse was the case – that he made the signal that the draw was open and the bridge, of course, impassable. The fault, therefore, lies between these two men. An investigation will determine upon which the dreadful responsibility must rest.

The draw being thus open, the advancing train leaped into the chasm.

The engine went first and was buried in the mud so deep that at low water it was out of sight. The engineer, who says he had reversed his engine, saved himself by leaping off at the abutment of the bridge. The fireman saved himself in a similar manner. The baggage and smoking car in which there were a number of persons, fell upon the engine, followed by two passenger cars; a third passenger car fell halfway down, end broken in two, a portion of the passengers falling into the water, while others managed to save themselves, some of them being injured. The first passenger car contained some forty persons, many of whom were rescued through the roof. The baggage-car, when it struck the engine was much broken up, and the persons in it killed.

One of the passenger cars was wholly submerged, and every person in it suppose to drowned.”

The engineer, Edward W. Tucker testified, “I believe I was going at the rate of fifteen miles per hour past the Norwalk depot; I whistled for breaking up just west of the bridge over the road coming up to the depot; I am certain the ball was up; I cannot be deceived; I did not look through the window glass, but entirely out; I do not think I could have been mistaken anything for the signal; I can see the signal just before I got to the bridge; I am certain I saw the signal; I am very careful…I sounded the whistle the moment I saw the end of the draw; the brakes were not applied for if they had been, I think the train might have stopped before going off the bridge…”

The bridge keeper, William Harford, testified, “As near as I can remember, it was fifteen minutes from the time I started the draw to close it before the train went over… I then lowered the ball and laid it on the bridge. I kept the bridge down a few minutes and listened if I could hear the train coming… I only heard the whistle as the train came around the curve; the whistle was blown twice; I heard no bell…that is my opinion as near as I can guess the length of time; I have not seen the engineer, and I don’t want to see him hardly.

Other persons testified that the ball was in a down position indicating the bridge was open. A total of 46 people were killed and 85 injured.

A coroner’s inquest found, in part: The immediate cause of this disaster was the negligence and recklessness of the said engineer.

20 STRUCTURE magazine

1st – In running around the curve at a rate not less, certainly, than twenty miles per hour; when under the circumstances should have been half that.

2 nd – In not discovering that the ball was down immediately after emerging from the cut.

3 rd – In not looking for the ball at the highway crossing east of the depot.

4 th – In relying, as he says he did, upon the flags of the switch-tenders, when he well knew that they were not in sight of the draw, and had nothing to do with it.

5 th – In not running even slower than usual when the track was wet and slippery.

In addition to all this, he well knew that the draw was required to be very frequently opened. In not discovering that the ball was down, we think he was guilty of gross negligence. In running around the curve at this rapid rate, and under such circumstances, we think him guilty of the most criminal recklessness.

At the same time, we do not think the entire responsibility of this disaster rests upon him. As we have before observed, the rules of the company do not make it the duty of the conductor to observe the signals, nor are we prepared to say that they should.”

Appleton’s Magazine had a lengthy article on the disaster, writing: “There were three other causes conspiring with this temporary carelessness, or the result would never have been experienced. First, the curve in the road and a number of intervening objects shut the signal out from view during a considerable portion of the immediate approach to the bridge. Second, the color of the signal had faded by exposure from a bright vermillion to a reddish-brown. The third, and principal, is the fact that, at the distance of some half a mile, the point where the eye of the engineer first meets this signal of safety, it is exhibited not standing out against the sky but against a distant wood, any dark spot in which might, in the temporary stupid condition supposed, be taken for the signal. This is the theory we have formed, and confidently believe in, at the present moment. The only look at the signal was made mechanically, on first emerging from the bridge; at this distance, some dark spot in the background was made to answer the purpose, and the fated train swept on till near the bridge before the absence of the accustomed signal flashed on his lethargic brain.”

The coroner’s report was carried in full in many newspapers later in May 1853 and was signed by all 12 members of the Jury. Tucker and Comstock, the conductor, were charged with manslaughter, but both were acquitted. Death claims amounted to about $290,000, which almost bankrupted the railroad. The state legislature passed a law that required all trains to come to a complete stop before proceeding across any swing span, agreed to by Appleton’s. In the early years of the development of the American Railroad, this was the worst disaster on record and, as is often the case where there is loss of life, Legislatures overreact as they did here. Making the train stop before proceeding, while safe, requires a longer time for the train to get from point A to point B thus negating the economic advantage of the railroad, its speed.■ Dr. Frank Griggs, Jr. specializes in the restoration of historic bridges, having restored many 19 th Century cast and wrought iron bridges. He is now an Independent Consulting Engineer. (fgriggsjr@twc.com)

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Addition, Renovation, and Rehabilitation at Hotel Julian

By David Nickell, S.E., Martin White, S.E., and Roger Reckers, S.E.

he condition of the building certainly did not match its high-profile location. For years, the existing 12-story building at 168 N. Michigan sat vacant on one of Chicago’s busiest thoroughfares. With an address on Michigan Avenue near the northwest corner of Millennium Park, countless residents and tourists would pass by each day. This empty shell was a once-prominent structure that had fallen into disrepair due to previous renovation attempts that were abandoned in mid-construction. Pieces of the original terra cotta façade had been removed, openings had been created in exterior walls and left uncovered, and the interior was in a similarly poor condition (Figure 1). During the design team’s walk-through at the beginning of the project, water that had penetrated the unsealed roof and traveled down 12 levels could be seen puddling on the basement slab.

The structure was originally constructed in 1911 as a bank office building and for decades occupied a place on the historic “Michigan Avenue Street Wall.” It utilized the popular structural system, of that era in Chicago, of clay tile flat arch slabs spanning to steel I-beams and built-up steel columns. These columns extended to concrete-encased steel grade beams and hand-dug concrete caissons. The lateral system consisted of masonry infill shear walls in the long direction of the building and built-up steel girder moment frames in the short direction.

Structural Scope The original programming goal of providing a 200+ key boutique hotel ultimately required a structural scope that could be split into two categories: addition and renovation/rehabilitation.

The addition came in the form of six new levels rising above the top of the existing structure, increasing the total building height from 160 to 240 feet and the square footage from 70,000 to 100,000. This significant increase required changes to the existing structure, renovations to accommodate programming changes, and repairs to in-situ conditions.

Addition The rehabilitated exterior façade facing Michigan Avenue. Courtesy of Anthony May.

22 STRUCTURE magazine

The design team’s first task was to assess the capacity of the existing structure to support the increased gravity loads

from the 6-story addition. Field measurement and documentation of each column lift were required due to a lack of column information in the original structural drawings. Small coupons of the existing steel were taken and analyzed by a testing agency to determine the yield strength, ultimate strength, and weldability of the steel. Sonar testing of the existing concrete caissons, performed by the geotechnical engineer, was completed to determine the bearing depth and used to provide a design bearing capacity.

After a thorough review of the existing drawings and subsequent field investigation, structural analysis revealed that the existing columns and caissons were adequate to support the weight of the new addition. This was anticipated by the design team, based on a table listing assumed dead and live loads for future stories on a scrap sheet of the existing building drawings.

Unfortunately, it did not appear that the original designers accounted for the lateral load of a new addition.

Although the 80-foot-tall addition increased the height by only 50 percent, it more than doubled the overall overturning moment on the building. The existing masonry shear walls (resisting loads against the short face of the building) were determined to be structurally adequate. However, the existing moment frames at the front and back of the building (resisting loads against the long face of the building) had no excess capacity to resist the new loads.

A full-building 3-D analysis utilizing ETABS software revealed that all components of the moment frames were overstressed, from the bearing capacity of the existing caissons to the stress in the columns, plate girders, and riveted connections.

Additionally, deflections were determined to exceed the industry standard limits. This major shortcoming of the existing lateral system, but the adequacy of the gravity system, is most likely attributed to advances in lateral analysis and changes in code-required wind loads over the past century.

Each moment frame would need to be wholly retrofitted or a new solution would need to be devised.

Strengthening the existing moment frames was considered and found to be infeasible since the size of the existing caissons limited the capacities of the

Figure 1. The exterior faรงade facing Michigan Avenue at the outset of the project.

Figure 2. One of three new braced frames erected in the existing building.

frame. Therefore, an alternate system was required that would not disrupt the occupiable space, that could be erected inside of an existing structure, and which was stiff enough to draw load away from the moment frames.

The solution was to install a hybrid lateral system consisting of two components throughout the full height of the existing 12-story building: 1) Three new braced frames (Figure 2) adjacent to the elevator shafts were used for the main supplement to the existing lateral system. New columns were erected between the existing double I-beam girders and HSS braces were installed within the shaft walls at each level, extending down to the existing steel grade beams and up through the new addition. This allowed the new lateral component to fit seamlessly into the building while not impacting the architectural intent of the space.

2) The steel braced frames were coupled with double angle steel knee braces (Figure 3, page 24 ), installed at approximately 175 locations throughout the interior of the building. This turned the existing interior double I-beam girders into link beams between the steel brace frames and knee braces.

This provided the additional lateral stiffness required to draw load away from the exterior moment frames.

This approach required local reinforcement of the existing columns against prying effects on the riveted built-up steel columns, but maximized the excess axial and bending strength of the interior columns.

In conjunction with the analysis and engineering associated with reinforcement of the existing structure, the six stories of the addition were also designed. Although the design of the new framing was straightforward, erection of the framing posed a significant challenge to the contractor.

The constrained project site did not permit the use of a tower crane for steel erection. Neighboring buildings are present on the north and south sides, while the building is bounded on the east and west sides by public streets that could not be obstructed (Michigan Avenue and Garland Court, respectively). Instead, the design team and contractor collaborated to develop FEBRUARY 2020

23

Figure 3. These double angle steel knee braces were installed at approximately 175 locations throughout the interior of the existing building.

Figure 4. A typical level showing extensive demolition of the existing clay tile slab.

a method of supporting mobile cranes on the highest constructed floor in order to erect the next floor above, then raising the crane to that floor and continuing the process. For the first floor of the addition, the existing roof, this required reinforcement of existing beams and installation of a new composite slab-on-deck located inches above the existing clay tile slab. This floor and the subsequent floors above were designed for two uses: the load imposed by the mobile cranes during construction and the code-required loading in the final condition.

Renovation / Rehabilitation The project also required significant renovation and rehabilitation to convert an early 20th-century building into a modern hotel, due primarily to the building’s condition at the start of the project.

There were multiple periods of vacancy during its 105-year lifetime, including immediately before the project start. Water infiltration and exposure to the weather had compromised portions of the clay tile slab and caused significant corrosion of the steel framing in select areas. Some specific areas of rehabilitation included: • Steel beams throughout the existing building were reinforced or replaced due to corrosion. The most extensive rehabilitation occurred at the existing roof, where full bays of steel beams were removed and replaced due to the extent of section loss. Investigations of the various conditions were performed to determine whether the beams were to be reinforced with plates or replaced with new beams.

• Previously abandoned renovation attempts created openings in the existing clay tile slab around nearly every existing column (approximately 200 locations) (Figure 4 ). These areas, combined with new demolition due to programming requirements, were infilled using a cast-in-place concrete system developed to reduce construction time and costs compared to a slab-on-metal deck infill. This was achieved by eliminating the need for field welding new beams and metal deck to the existing painted steel I-beams, which would have required costly lead abatement before welding.

Eliminating the need for new steel beams at the perimeter

24 STRUCTURE magazine

of the openings also proved to be a key advantage due to the irregular sizes and shapes of the openings in the existing slab (Figure 3).

• The condition of the existing clay tile slab was reviewed throughout the building to identify areas of possible deterioration. Clay tile flat arch slabs are an archaic slab system that is susceptible to water damage in the mortar placed between the clay blocks. Standard patching/repair details were employed as much as possible, but several locations required complete removal of the existing slab.

The aforementioned cast-in-place concrete infill method was used to replace the existing slab at these locations.

New Life for an Old Master The existing building in the heart of Chicago’s downtown, once a candidate for demolition, received a much-needed rehabilitation.

However, this was only part of the story. The ambitious goal of adding six levels to a 105-year-old building created an architectural highlight that stands out on this busy section of Michigan Avenue. Hotel Julian is now a modern hotel with a structure as impressive as its coveted location.■ David Nickell is a Principal at TGRWA in Chicago and is a past President of the Structural Engineers Association of Illinois (SEAOI). (dnickell@tgrwa.com) Martin White is a Senior Structural Engineer at TGRWA. (mwhite@tgrwa.com) Roger Reckers was the Principal-in-Charge at TGRWA. (rreckers@tgrwa.com)

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The Key th at 12

Salvaging History: Oakland’s Structural Rebirth

By Peter W. Somers, P.E., S.E.

Figure 1. Design vision. Courtesy of Gensler.

T

he Key at 12th is an 18-story office development in the heart of the central business district of Oakland, California. In an area where construction is booming and old buildings are being demolished all over the city to make way for modern facilities, Magnusson Klemencic Associates (MKA) was intrigued by the idea of designing a tower that repurposed a building rather than leveling it. Engineers worked sideby-side with architects and contractors to create a new structure that integrated the adjacent historic building, the 8-story Key Systems Building (KSB), into a combined development of 334,000 gross square feet (Figure 1). The project includes ground-floor retail, two occupied roof terraces, and is located next to a transportation hub.

The Key at 12th is a textbook example of how the AEC industry can meld modern design with classic architecture, proving that progress can coexist with preservation.

a hotel and office. One project began installing approximately 80 precast piles on the bare site, and another project contemplated demolishing all of the KSB except for the façade and integrating the façade into a new building. Both projects stalled and were ultimately abandoned due to financial considerations, in part because of the cost to integrate the historically significant building but also because attracting tenants to a difficult site proved challenging.

Finally, in 2017, Ellis Partners purchased the site and engaged Gensler to design an office building that integrated the KSB into the project in a manner that salvaged the existing structure while providing Class A office space. Preserving the KSB was a critical feature in successfully navigating the entitlement process, while creating a maximum-sized and highly-functional office floor plate was essential for attracting top-tier tenants (Figure 2).

Site History

Project Vision

The Key at 12 site occupies approximately one-third of a city block bounded by Broadway, 11th Street, and 12th Street, and originally contained the KSB and several low-rise structures. Significantly damaged in the 1989 Loma Prieta earthquake, the low-rise buildings were demolished and their one-level basements were filled with rubble up to grade.

The KSB was also damaged and, unfit for occupants since the event, it stood vacant for the last 30 years.

Several development projects had been proposed for the site, including

Combining the dual goals of historic preservation and modern office design, the team configured a floor plan with a side-core layout to maximize the size of the office floor plate adjacent to Broadway, placing the elevators, stairs, and other core functions on the west side of the site, adjacent to another 12-story office building located on the property line. The building is split – the lower levels (1 through 8) combine a new structure with the existing KSB while the upper levels (10 through 18) are new construction. Gensler’s design merged new with old and function

th

26 STRUCTURE magazine

Figure 2. Existing site with historic KSB building. Courtesy of Gensler.

with form. The higher levels of office feature floor plates that cantilever approximately 25 feet over the KSB, resulting in maximum space and a design feature that combines and contrasts with the KSB. The structural system consists of light-weight concrete slabs on composite steel decking, supported by steel framing. The cantilever is supported by two-story steel trusses located on the three exterior sides. To avoid interior trusses, MKA designed an approximately 100-foot-long exterior truss at the end of the cantilevered bay that transfers loads to 25-foot-long cantilever trusses located on the east and west perimeter sides of the building.

The tower’s lateral system consists of buckling-restrained braces (BRBs) and is comprised of single-story bracing configured in an E-shape at the core and two-bay, multi-story braces on the east side of the building to control torsion due to the offset core. With a roof height of 240 feet, the building is designed using the prescriptive requirements of ASCE 7-10, Minimum Design Loads for Buildings and Other Structures.

The foundation consists of a mat under the core on the western two-thirds of the site and a pile-supported grade beam on the west side of the site.

Integration of the Key Systems Building A central feature of this project was to bring new life to the vacant and dilapidated KSB. The building, constructed in 1911, is a steel-frame structure with concrete floors and masonry exterior walls. Consistent with buildings of this vintage, the structure did not have a well-defined lateral system. Rather than add intrusive and space-constraining new lateral elements within the KSB, the design solution was to use the

Figure 3. Lateral system plan summary.

new tower to buttress the existing KSB by adding diaphragm ties and collectors (Figure 3). The new tower’s lateral system was proportioned based on the mass of the KSB and designed to be stiff enough to protect the existing, brittle, exterior wall systems at the KSB. A series of north-south oriented collector elements were added at each floor to tie the KSB into the new tower diaphragms.

The existing south exterior masonry wall was removed after the two structures were connected to allow clear access between the KSB and the new tower. Also, the line of exterior columns located at the former perimeter walls was removed to provide a more substantial open office space. The relatively close-spaced columns (approximately

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15 feet on-center) did not align with the columns of the new tower and would have created a forest of columns at the transition between the two buildings. The existing KSB framing that had been supported by these columns is now supported by cantilever steel beams extending from the new building columns. MKA worked closely with the contractor to sequence both the masonry wall and column removal to avoid extensive temporary shoring. Occupants will have an unobstructed view from the new building into the restored brick walls and wood windows of the KSB.

Lateral System Design To minimize the building’s weight Figure 4. Lateral system elevation. and to provide more flexibility at the interior of the side-core layout, a steel-braced lateral system was selected for the project. It was determined that an all-steel structural system was faster to erect than a concrete core. A braced frame was placed at the eastern perimeter along Broadway to control torsion and satisfy the requirements in ASCE 7-10 for the height increase to 240 feet for braced frame structures. To reduce the number of braces, provide a more open façade, and to meet the design intent of the architect, this perimeter brace is arranged in a multi-story “X” configuration and celebrated as a design feature visible through the curtain wall. The core bracing, which is generally hidden from view, was configured as single-story bracing in a chevron pattern to minimize the unbalanced loading on the beams.

The main design challenge with the BRB lateral system was the interaction with the trusses supporting the cantilever. MKA’s design solution was to provide a two-story “elastic” zone at the level of the trusses (Figure 4 ).

Standard BRB framing exists above and below this level, but the two levels of truss floors utilize wide flange bracing designed for amplified seismic forces (omega) to force BRB yielding either above or below the transfer level. In addition, the trusses themselves were designed for gravity loads plus amplified seismic forces based on the relative lateral stiffness of the trusses compared to the other bracing elements on these floors. Ductile seismic performance is assured

through yielding in the BRB elements, and stability is protected through the strength of the elastic zone elements.

The BART Influence The Bay Area Rapid Transit (BART) system plays a significant role in the design of a building as engineers must consider and strategize ways to adapt a structure’s foundation around the tunnels. This poses many challenges. BART requires new developments adjacent to their tunnels and underground stations to limit any loading within the Zone of Influence (ZOI) to no more than the current load on the site. The ZOI is defined as a line starting from the lowest point of the BART structure adjacent to the subject property and extending up at a slope of 1.5 horizontal to 1 vertical until it hits grade (Figure 5).

While downtown Oakland benefits from relatively good soils and an 18-story building using a light-weight steel structure could generally be supported on shallow spread footings or a mat, the proximity of the tower to the BART station required a different approach – deep foundations. Based on the depth of the tunnel and proximity to the site, the ZOI crosses the basement level approximately one-third of the way into the site. Therefore, all structural elements located in this third of the site needed deep foundation elements to transfer the load below the ZOI. The Key at 12th utilizes double-cased auger cast piles (24-inch piles within 33-inch steel casings) above the ZOI that are effectively free-standing concrete columns within the ZOI. Lateral forces are transferred from the perimeter braced frame back to the mat foundation through a basement-level transfer slab.

The site beyond the ZOI is founded on a concrete mat that varies from 5 to 7 feet at the core. The column layout for the tower was based on three bays in the east-west direction with the first interior column located on the mat foundation. However, during design, additional as-built information on the BART tunnel depth revealed the tunnel to be slightly deeper than initially anticipated. This required the mat’s leading edge be thickened by 4 feet to bear outside the ZOI.

A Development for Oakland’s Future Expected to open in early 2020, The Key at 12th continues the rebirth of downtown Oakland while preserving one of the architectural treasures of its history. As cities continue to change, grow, and modernize, projects such as the Key at 12th show that we can successfully integrate old and new construction.■

Figure 5. Foundation concepts.

28 STRUCTURE magazine

Peter W. Somers is a Principal at Magnusson Klemencic Associates. He is the leader of MKA’s Existing Buildings Technical Specialist Team, Past President of the Seattle Chapter of the Structural Engineers Association of Washington, and actively involved in structural engineering code development, particularly those related to the renovation of existing buildings. (psomers@mka.com)

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Hale Centre Theatre TRULY ONE OF A KIND

By Tait A. Ketcham, S.E., and Darren G. Dickson, S.E.

H

ale Centre Theatre in Sandy, Utah, is a world-class theater expeThe overall building height is primarily driven by the requirements rience that is truly one of a kind. It features a centrally located for the stage – clearances required over the stage, catwalks, and round stage with seating radiating concentrically outward, subsequent clear height required for the overhead crane systems or each row increasing in diameter. When patrons experience a show at “bogies.” These combined requirements resulted in a total structure Hale Centre Theatre’s center stage, the viewing angle is 360-degrees. height of just over 158 feet, with approximately 90 feet above exterior The Theatre is approximately 130,000 square feet with two separate grade and 68 feet below grade. The perimeter walls of each theater stages. The theater-in-the-round seats over 900 patrons and the smaller are 18 inches thick, designed to meet the stringent sound transmisJewel Box theater seats 460 people. The total construction cost of the sion requirements as well as act as the primary lateral system for the building was $80 million, of which $20 million was allocated to the building. Due to the quantity and thickness of the walls, the shear stage technology and overhead crane systems. What makes this theater demand due to seismic loads is relatively low. The more significant unique is the stage and crane system technologies incorporated into design issue was adequately connecting these very tall and heavy walls the design. TAIT Towers from London, England, was the designer to the diaphragm for out-of-plane loads. The tallest individual wall and installer of these systems. About Hale Centre Theatre, they have was 116 feet above the footing. One interesting fact is that, due to stated: “You will not be able to find a lift system or overhead crane this height and thickness, the resulting concrete yield calculates to system like this anywhere.” These high-tech systems created several over 6.5 cubic yards of concrete per linear foot of wall. unique structural design challenges for the structural team.

The radiused suspended seating is also one of the most unique The round revolving stage was designed to provide 20 feet of vertical aspects of this project. To allow for two slip stages used to cover stage travel. This required the overall stage structure to be at a height of 40 openings when the stage is lowered to the pit level, the seating was feet. The theater was designed to have the stage level 14 feet below grade. required to be suspended. These slip stages retract below the seating The level that supports and houses the round stage and ancillary equip- on opposing sides. The beams for seating matched the radius of the ment is known as the sub-pit, which extends an additional 40 feet below stage and had to span to sloping beams, creating large torsion effects. the pit level. The existing groundwater table was approximately at the This resulting thrust was resolved with tube sections at strategic points elevation of the stage, compounding along the radius beams extending the challenges. Many options were up the seating and into the floor vetted, and the resulting design was diaphragm at the top of the seatto permanently dewater 14 feet (to ing. Directly over the slip stage, at pit level) and design for hydrostatic the bottom of the seating, it was and buoyancy pressures reaching required to maintain the typical over 40 feet at the bottom of the 21-inch step between seating rows. sub-pit. The resulting design hydroAs a result, a very shallow structure static uplift pressures exceeded 3000 was required to still allow for the psf. The structural design utilizes a 16-inch-deep slip stage and associ52-foot inside diameter, 18-inchated clearances. The design utilizes thick wall that acts as a compression cantilevered tubes in-plane with ring to resist the water pressure the deck that results in a strucforces. The walls are supported on tural depth of only 4 inches at this a 36-inch-thick continuous mat lowest row of seats. footing underpinned with twentyOne of the governing factors in nine 16-inch round steel pipe piles the design was to have a columnextending over 70 feet below the free space within the viewing area Aerial view showing the subpit compression ring. mat footing. of the theater. Also, the “Loading 30 STRUCTURE magazine

Loading level framing supporting a suspended three-tiered catwalk below.

900-ton crane hoisting 6-foot-deep plate girders.

Level” above the stage and seats was to be used as a storage space for show sets, props, wardrobe, and other support spaces for the theater production. The resulting design has four main columns within the box of the theater that provide the majority of the load support for the floor and the roof above. This level is approximately 36 feet above the seating and designed with 125 psf storage loading. The design utilizes six-foot-deep, built-up plate girders. Four of the girders span 110 feet to two transfer plate girders spanning up to 107 feet. The weight of the transfer girders exceeds 700 plf.

This level also supports all the catwalks that encircle the space above the stage and seating areas. The catwalks are suspended from this level using tube column hangers resulting in the column-free space desired in the viewing area.

The clearance above the Loading Level was driven by the height required to support two 15,000-pound overhead cranes or “bogies” with 4,000-pound payloads and the associated hoisting requirements for each. One concern for the bogie support is that the hoisting requirements are exact, down to 1⁄8 inch. Keeping snow load deflections within this limit, while allowing precise calibration of the hoists, was not realistic within the same structural system. This also was not acceptable from a safety standpoint. The solution was to support the bogies from two trusses that are supported independently from the roof. The result is two steel wide flange trusses that span 138 feet and are independent of the roof. The trusses are braced laterally to the exterior walls via a series of struts and ties. The trusses have been designed to limit the maximum deflection of 1 inch while under full loading of the bogies in a dynamic loading condition.

In addition to design challenges, there were many construction challenges for the contractor, Utah-based Layton Construction. For example, constructing the sub-pit that extends approximately 54 feet into the groundwater. The contractor decided to install steel sheet piling in a circle, slightly larger than that required to construct the round sub-pit. The circular geometry was chosen over a square because it allowed for a compression ring to brace the sheet piling while excavating without adding horizontal tiebacks or internal bracing that would create future construction conflicts. Then a series of construction wells were constructed to draw the water down.

In addition to the depth into the ground, the height above grade was also a significant challenge to construct. With very thick and heavy walls that extend up to 116 feet above the footing, constructing these walls before any floor diaphragm being in place was a significant concern. Close collaboration between the contractor’s construction approach and the wall design allowed the contractor to build and sequence the construction in a manner that met the project schedule.

An additional interesting construction challenge that required collaboration was the installation of the large plate girders. The concrete walls were required to be constructed for the full height of the structure, so a 900-ton crane was over 90% utilized to hoist the furthest girder into place, over 125 feet away from the crane set-up location and 90 feet over the wall. Due to the proximity of the crane outriggers to the basement wall, the wall was designed to accommodate the 450-kip outrigger reactions caused by the crane. The resulting outrigger pad consisted of 15- x 20-foot bearing mats of 12- x 12-inch wood timbers with an additional 10-inch x 8-inch x 15-foot solid steel bearing pad on top of the wood mat. The resulting bearing pressure was near 1400 psf.

From the outset, the owner’s goal was to create a world-class venue that would attract theater-goers from all continents. The unique design issues from a structural perspective were challenging, but, in the end, add significantly to the overall experience of the venue.

Hale Theatre’s mission is to provide innovative, professional family theatre education that involves and elevates the community.■ Tait A. Ketcham is the President at Dunn Associates, Inc in Salt Lake City, Utah, and Engineer of Record for this project and Past President of the Structural Engineers Association of Utah. (tketcham@dunn-se.com)

Suspended radius framing for seating with cantilevered tubes at bottom row to allow the slip stage to retract beneath the seats.

Independently supported “bogie” truss system.

Darren G. Dickson is a Senior Associate at Dunn Associates, Inc in Salt Lake City, Utah. (ddickson@dunn-se.com)

FEBRUARY 2020

31

INSIGHTS Design-Build and the Structural Engineer A Call for Leadership

By Ciro Cuono, P.E.

D

esign-Build, though not new as a delivery method for building projects, appears to be on the rise. Traditionally known as the Master-Builder method, it is a means of building where one party holds responsibility for both the design and the construction. The Master-Builder method was the only method before the now ubiquitous design-bid-build project structure. The Romans for example, famous for their roads, aqueducts, and amphitheaters, did not design a project, bid it out to subcontractors, and then select the low bidder to build it, but rather designed and built structures in a collaborative, somewhat simultaneous fashion. In building a house for a client during Colonial times, one party, such as a master carpenter, was responsible for delivering the general layout and exterior details, selecting structural members, and completing construction. In this way, the carpenter acted as the architect, engineer, and builder simultaneously. The concept of design, bid, and build arose out of the natural specialization of the architect, engineer, and builder in the post-1850s world, where modern structural engineering was born and separated from architecture, and architects and builders fully separated as distinct and separate entities.

A century ago, an architect or engineer might be expected to design both the structural framing of a building and the heating and cooling equipment. However, the building environment of today, like most fields, is continually becoming more specialized and complex. Every 3 years, codes get a little thicker, new products and techniques continuously come online, and more highly specialized knowledge is developed.

Given the development of the field into specialized areas and the foreseeable continuation of high-depth knowledge, the idea of a single person Master-Builder is virtually impossible. Just like a country doctor in another era may have acted as an internist, surgeon, and obstetrician, today that would be unheard of, impracticable, and potentially dangerous.

Therefore, the Master-Builder paradigm can only exist as a team effort among a group of specialists – an oligarchy of architects, engineers, and builders who work together to design and build a joint project as one team.

32 STRUCTURE magazine

While the idea of design-build is not new, I believe it will continue to gain more market share in the AEC industry for a few reasons: 1) Technology: 3-D modeling programs, ease of file transfer and sharing.

Greater technological sophistication of builders all will lead to increased and more natural collaboration.

2) Competition: Increased competition in the AEC industry as a whole, including from emerging firms abroad, will lead to innovation, including inventiveness of delivery methods and construction techniques.

3) Prefabrication: Prefabrication of building components and whole buildings is likely to increase. This will doubtless be a natural evolution from 3-D modeling and manufacturing technology. Prefabrication of components like concrete panels and structural insulated panels is basically a design-build endeavor. It seems logical that this will eventually extend to whole buildings and, therefore, the whole design and build effort.

In the current state of practice, most designbuild projects are either builder-led or architect-led with some exceptions. In builderled projects, a general contractor provides design-build services and hires an architect and consultants to provide the design. In contrast, in an architect-led project, the architect, in conjunction with consultants, designs the projects and then hires a general contractor or acts as a construction manager and hires the various sub-contractors. In either case, the structural engineer is not in charge. Why is this? Why can the structural engineer not be in charge?

Structural engineers design the primary and most crucial part of a building and we lead, in the literal sense, the construction effort. After all, buildings are not mechanical systems or excavation sites or facades – they are structures, and structure always goes first.

One can envision a future where structural engineers seize a leadership role and morph into a design-build paradigm in which they own and operate companies that design and build the foundations and framing systems of buildings and have, on staff, collaborative and capable specialists such as architects,

technicians, civil and mechanical engineers, and seasoned construction professionals. In this concept, an Owner still retains a design Architect to put the Owner’s vision on paper (or in a model) and then the Owner hires a company to complete the design and build it.

In this vision of the future, a company that the Owner hires is a design-build company led by structural engineers who complete a traditional design role and act as master coordinators for the rest of the design and construction effort with fellow specialists.

Currently, in some states, a design-build model, as outlined above, is not allowed under one entity, and the design needs to be under a separate contract. However, the benefits of this design-build system are many. First, this would put structural engineers on top of the food chain, leading to more consistency in fees. Fees would no longer be simply fees but would have to be truly thought of as a percentage of the entire construction cost. Secondly, this would lead to greater efficiency of design.

Designs could be more daring and less simplified if the structural engineer knows they have control over what happens in the field.

Thirdly, working cooperatively and directly with sub-contractors who build structures (an invaluable experience that many structural engineers have had) would bring better and direct training in constructability and practicality. Additionally, this forced leadership role would elevate structural engineering practice and help to attract future talent.

I view this model as the future of our business, coming full circle to something close to the Master-Builder idea, albeit through broad-scale cooperation of highly trained specialists in varied backgrounds. While this model may not be attractive to all structural engineers, the idea of leadership and collaboration should be a goal common to all engineers.■ Ciro Cuono is the Founding Principal of Cuono Engineering PLLC, a structural engineering firm located in Port Chester, NY, and NYC, and is a past Assistant Adjunct Professor at The Bernard and Anne Spitzer School of Architecture at the City College of NY. (ccuono@cuonoengineering.com)

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NCSEA NCSEA News

National Council of Structural Engineers Associations

NCSEA Hosts Timber-Strong Design Build Competition at ’19 Summit In partnership with the American Wood Council, Simpson Strong-Tie, and APA–The Engineered Wood Association, NCSEA brought the Timber-Strong Design BuildSM Competition to the 2019 Summit in Anaheim, California. This “hands-on” competition, designed for university engineering students, provided a real-world experience in both planning and building a wooden structure within a team environment.

Student teams were required to submit the design of their structure along with a report that calculated the carbon footprint of the structure as well as the cost of materials. The building portion took place on November 12th at the Disneyland® Hotel where six teams competed to build a two-story wood structure within 90 minutes. The six teams represented schools from four states: California (California State University-Sacramento, University of California-Los Angeles, and California Polytechnic State University – San Luis Obispo,), Kentucky (University of Kentucky), Minnesota (University of Minnesota – Twin Cities), and Florida (University Students from Calfornia Polytechnic building their of South Florida). structure.

As volunteers taped off the parking lot indicating where each school would be doing their build, the students arrived with their pre-fabricated panels, tools, and safety equipment ready to compete. The teams were not only required to keep their builds within the 90-minute time frame, but they were also required to keep all materials within a given area while they completed their structure. Structural engineer judges observed and scored aspects of the build while additional volunteers kept an even closer watch on the students’ safety as well as their correct use of tools and equipment. Once time was called, a verbal presentation was made by each team which included a display board to reference aspects of their design and build.

The winners were: 1st Place: California Polytechnic State University, San Luis Obispo 2nd Place: University of California, Los Angeles 3rd Place: University of Kentucky Teams were responsible for the deconstruction and removal of the structures, but with an added opportunity: schools were given the option to donate their structure to the Childhood Cancer Foundation of Southern California (CCFSC). In turn, the CCFSC would give it to one of their patient’s families to be reassembled in their backyard. Three schools donated their creations. As a special highlight of the day, a young patient and her family attended the build and she was able to choose which structure would be reassembled in her backyard, courtesy of the support of Simpson Strong-Tie employees. As a memento of the young patient’s attendance at the event, NCSEA gave a hardhat with the Council’s logo as a remembrance of the day.

The representative from the Childhood Cancer Foundation of Southern California posing with strudents from UCLA who built the playhouse she chose.

2020 Excellence in Structural Engineering Awards NCSEA's Excellence in Structural Engineering Awards annually highlights some of the best examples of structural engineering ingenuity throughout the world. Projects are judged on innovative design, engineering achievement, and creativity. Multiple winners are presented in eight categories with an outstanding winner chosen from each category. The winners will be honored at NCSEA's Structural Engineering Summit in Las Vegas, Nevada this November.

The awards are presented in the following categories: • New Buildings under $30 Million • New Buildings $30 Million to $80 Million • New Buildings $80 Million to $200 Million • New Buildings over $200 Million • New Bridges or Transportation Structures • Forensic/Renovation/Retrofit/Rehabilitation Structures under $20 Million • Forensic/Renovation/Retrofit/Rehabilitation Structures over $20 Million • Other Structures Entries are due on July 14, 2020. Structural engineers and structural engineering firms are encouraged to enter. More information about the awards along with submission instructions can be found on www.ncsea.com.

36 STRUCTURE magazine

News from the National Council of Structural Engineers Associations Communications Committee's First Public Outreach Challenge Roars NCSEA's Communications Committee challenged NCSEA Member Organizations to inform and educate other industries, professions, and the general public about Structural Engineering through the publication of news articles, videos, blogs, and other creative content.The SEAs were asked to submit a portfolio of content generated over the past two years, which the judging panel would score based on both quantity and potential audience.

The Member Organizations that participated in the inaugural challenge submitted over 300 individual pieces of content. Three MOs were recognized as finalists at the NCSEA Structural Engineering Summit in Anaheim, California, in November. Finalists each received a shake table for use in their public outreach efforts. From these finalists, a winner was selected and named the Voice of the Profession.

Third Place: Structural Engineers Association of Oregon (SEAO) SEAO members contributed to several print articles in publications from college alumni magazines and firm blogs to regional and local business journals. Members also discussed structural engineering at a high school engineering contest and as a member of a community disaster preparedness panel.

Stand-Out Contribution: bit.ly/39W3flf Published in a prominent regional business newspaper, this article, authored by an SEAO Structural Engineer, took advantage of a recent seismic event in the area to capture the general public’s attention and address key concerns of nearby residents, while highlighting the impact of structural engineering in a way the public can understand.

Second Place: Structural Engineers Association of Illinois (SEAOI)

Maria Mohammed, chair of SEAOSC's Communications Committee, accepting the "Voice of the Profession" award on behalf of SEAOC.

SEAOI generated a wealth of technical articles for industry publications, assisted with numerous articles for both local and major newspapers, and expanded to electronic media with podcasts, YouTube videos, and a healthy social media presence.

Stand-out Contribution: bit.ly/2R61pFW Published in a prominent newspaper, this article uses the public’s existing interest in a new Chicago skyscraper to explain how seemingly aestheticonly features are also intentional, and teach the general public structural engineering basics through easy-to-understand graphics.

First Place and Voice of the Profession: Structural Engineers Association of California (SEAOC) SEAOC submitted a comprehensive package of over 60 individual articles and initiatives undertaken by its members, demonstrating a significant impact on public education about the structural engineering profession. Submissions ranged from social media posts, selfpublished MO newsletters, and podcast contributions to participation in press conferences, a steady stream of SE-related articles in local and major newspapers, and leadership within a regional Safer Cities program.

Stand-out Contribution: bit.ly/2uCRYWW The Safer Cities Advisory Program provides communities an avenue to engage structural engineers in the development and implementation of regulations and programs to mitigate seismic risk. MO members have built an impressive network of relationships with public policy makers and the general public through this program, improving their community’s safety, as well as the local perception and understanding of structural engineers.

NCSEA Webinars

Register by visiting www.ncsea.com

February 20, 2020 Basics of Strut and Tie Modeling

Royce Floyd, Ph.D., S.E.

This webinar will provide a general overview of strut and tie modeling based on the ACI 318 Building Code Requirements for Structural Concrete and Commentary. It will include discussion of situations where a strut and tie model is appropriate, strut and tie model development, and calculation of strut and tie model strength. The webinar will also include limited discussion of required detailing.

Courses award 1.5 hours of continuing education after the completion of a quiz. Diamond Review approved in all 50 states.

F E B R U A R Y 2 020

37

SEI Update New SEI/ASCE Titles

Life-Cycle Design, Assessment, and Maintenance of Structures and Infrastructure Systems is a state-of-the-art comprehensive report outlining current status and research needs examining: • The environmental impact on concrete and steel structures; • Strategies for assessing these deteriorating systems; • Life-cycle management concepts; and • Maintenance policies for these structures and infrastructure networks.

Recommended Practice for Fiber-Reinforced Polymer Products for Overhead Utility Line Structures, MOP 104, Second Edition, details best practices for the use of fiber-reinforced polymer (FRP) composite poles and crossarms in resilient conductor support applications. This new edition updates and expands on nearly every aspect of FRP pole and crossarm testing, design considerations, installation, and asset management, providing the line designer with another tool in the line design toolbox in addition to the traditional materials of wood, steel, and concrete. www.ascelibrary.org

Congratulations to the 2020 SEI Fellows!

The SEI Fellow (F.SEI) grade distinguishes members as leaders and mentors in the profession. Join us to recognize these new SEI Fellows at Structures Congress 2020, April 5-8 in St. Louis: Thomas Broz, P.E., S.E., F.SEI, F.ASCE Guy Lund, P.E., F.SEI, M.ASCE Karl J. Rubenacker, P.E., S.E., F.SEI, M.ASCE Peter Chase, P.E., F.SEI, M.ASCE Adolfo Matamoros, Ph.D., P.E., F.SEI, M.ASCE Benjamin Schafer, Ph.D., P.E., F.SEI, M.ASCE Karen Chou, Ph.D., P.E., F.SEI, F.ASCE Jamie Padgett, Ph.D, F.SEI, A.M.ASCE Shuxian Wassenius, P.E., F.SEI, M.ASCE Benton Cook III, P.E., S.E., F.SEI, M.ASCE Keith Porter, Ph.D., P.E., F.SEI, M.ASCE Chung Fu, Ph.D., P.E., F.SEI, F.ASCE Hayder Rasheed, Ph.D., P.E., F.SEI, F.ASCE Learn more about SEI Fellows and how to advance at www.asce.org/SEIFellows.

Three Reasons to Join SEI: A Perspective from a Graduate Student

By Antonio Zaldivar de Alba, S.M.ASCE, University of Illinois at Urbana-Champaign

First, joining SEI is completely free for students!

We all know the financial challenges of graduate school, so SEI/ASCE helps by making student membership free. Student membership comes with plenty of benefits such as discounts to attend conferences, STRUCTURE magazine, discounted membership for the first year after graduation, and much more.

Second, as an SEI student member, you are eligible to apply for an SEI scholarship to get involved at Structures Congress, and for the O.H. Ammann Research Fellowship in Structural Engineering.

Both can help you reach your academic and professional goals.

Lastly, and for me most importantly, you can get involved in an SEI Graduate Student Chapter (GSC). You can form one or join an existing Chapter if your university already has one. Being part of a GSC not only opens the door to opportunities inside your university but throughout SEI/ASCE. SEI GSCs can send a representative to the SEI Local Leaders Conference (LLC) with most of the expenses covered

by SEI. I had the opportunity to attend the SEI LLC in 2018 and I can tell you it is a great venue to expand your network by meeting

Errata 38 STRUCTURE magazine

leaders from student and professional chapters, developing leadership skills through specialized training, and discussing ideas to improve the structural engineering profession. Also, you can be a part of the SEI Graduate Student Chapter Leadership Council, where you will meet and collaborate with student leaders from other universities, learning valuable leadership skills.

As a graduate student, you are always busy with demanding courses, research, teaching assistant duties, volunteer work, and life! But I want you to know that SEI has opportunities for students with all levels of interaction and the benefits for all of them are plentiful. The more involved you get, the more you will be able to get out of it. SEI has allowed me to travel, meet people, improve my leadership skills, discover new ideas, and pursue my goals in structural engineering. I encourage you to expand your horizons and try everything that SEI has to offer – you will not be disappointed.

Antonio is a structural engineering Ph.D. student researching thunderstorm-generated wind loading. He has been an active SEI student member since he joined UIUC in 2015, has held leadership roles since 2018, and serves as the chair of the SEI Graduate Student Chapters Leadership Council.

SEI Standards Supplements and Errata including ASCE 7. See www.asce.org/SEI-Errata.

If you would like to submit errata, contact Jon Esslinger at jesslinger@asce.org.

News of the Structural Engineering Institute of ASCE

Announcing 2020 SEI Futures Fund Lecture Presentations March 19 April 27 May 6 July 16

Don Dusenberry, P.E., F.SEI, F.ASCE, on Performance-Based Design at SEI New Orleans Chapter Emily Guglielmo, P.E., F.SEI, M.ASCE, on ASCE 7-16 Seismic at SEI University of IL Urbana-Champaign Graduate Student Chapter Don Dusenberry on Performance-Based Design at SEI Oregon State University Graduate Student Chapter Kevin LaMalva, P.E., M.ASCE, on Structural Fire Engineering at SEI Colorado Chapter

Thank you to each of the speakers for generously sharing their time and expertise. Event details to be announced.

Learn more and give to support SEI Vision initiatives www.asce.org/SEIFuturesFund.

ASCE Week March 22–27, 2020 | Orlando, FL • Earn up to 44 PDHs • Register by February 28 for 25% off regular seminar prices • Choose from two private Disney tours! Earn up to 4 PDHs! www.asceweek.org

SEI Online

SEI News SEI on Twitter

Follow us: @ASCE_SEI

Read the latest at www.asce.org/SEINews

Standards SEI on Facebook SEI Visit www.asce.org/SEIStandards Follow us: @SEIofASCE

to View ASCE 7 development cycle F E B R U A R Y 2 02 0

39

CASE in Point Did you know?

CASE has tools and practice guidelines to help firms deal with a wide variety of business scenarios that structural engineering firms face daily. Whether your firm needs to establish a new Quality Assurance Program, update its risk management program, keep track of the skills young engineers are learning at each level of experience, or need a sample contract document – CASE has the tools you need!

CASE has several tools available for firms to use for recruiting and retaining employees.

962 962-B Tool 2-2 Tool 2-3 Tool 3-2 Tool 3-5 Tool 4-3 Tool 5-1 Tool 5-2

National Practice Guidelines for the Structural Engineer of Record National Practice Guidelines for Specialty Structural Engineers Interview Guide and Template Employee Evaluation Templates Staffing and Revenue Projection Staffing Schedule Suite Sample Correspondence Guidelines A Guide to the Practice of Structural Engineering Milestone Checklist for Young Engineers

You can purchase these and the other Risk Management Tools at www.acec.org/bookstore.

CASE Winter Member Meeting February 27-28, 2020

The 2020 CASE Winter Member Meeting is scheduled for February 27-28, 2020, in New Orleans. The agenda for the meeting includes:

Thursday – February 27 1:30 pm to 5:30 pm 6:15 pm to 7:30 pm

CASE ExCom Meeting CASE Project Speaker

Friday – February 28 7:30 am to 8:30 am 8:30 am to 10:00 pm 10:00 am to 10:30 am 10:30 am to 12:00 pm 12:00 pm to 1:15 pm 1:30 pm to 5:30 pm

Shared Breakfast CASE Roundtable – Stacy Bartoletti, Moderator Shared Morning Break Technology Panel Discussion – Kevin Peterson, Moderator Shared Lunch CASE Breakout Sessions

Registration can be found at www.acec.org/coalitions/upcoming-coalition-events.

Questions? Contact Heather Talbert at htalbert@acec.org.

Donate to the CASE Scholarship Fund!

The ACEC Council of American Structural Engineers (CASE) is currently seeking contributions to help make the structural engineering scholarship program a success. The CASE scholarship, administered by the ACEC College of Fellows, is awarded to a student seeking a bachelor’s degree, at minimum, in an ABET-accredited engineering program. Since 2009, the CASE Scholarship program has given $32,000 to help engineering students pave their way to a bright future in structural engineering.

We have all witnessed the stiff competition from other disciplines and professions eager to obtain the best and brightest young talent from a dwindling pool of engineering graduates. One way to enhance the ability of students to pursue their dreams to become professional engineers is to offer incentives in educational support.

Your monetary support is vital in helping CASE and ACEC increase scholarships to those students who are the future of our industry.

All donations toward the program may be eligible for a tax deduction, and you do not have to be an ACEC member to donate! Contact Heather Talbert at htalbert@acec.org to donate.

40 STRUCTURE magazine

News of the Council of American Structural Engineers CASE Practice Guidelines Currently Available

CASE 962-D – A Guideline Addressing Coordination and Completeness of Structural Construction Documents

CASE 962-F – A Guideline Addressing the Bidding and Construction Administration Phases for the Structural Engineer

These guidelines focus on the degree of completeness required in structural construction documents (“Documents”) to achieve a “successfully completed project” and on the communication and coordination required to reach that goal. They do not attempt to encompass the details of engineering design; rather, they provide a framework for the SER to develop a quality management process. Currently, the coordination and completeness of Documents varies substantially within the structural engineering profession and among the various professional disciplines comprising the design team. The SER’s goal should be meeting both the owner’s and the contractor’s needs by producing a complete and coordinated set of Documents. Owners and contractors generally understand that some changes to the Documents will occur because they realize that no set of Documents is perfect. The SER must focus on completeness, coordination, constructability, and the reduction of errors in order to minimize potential changes. A companion document is available: CASE Tool 9-1: Coordination and Completeness of Structural Construction Documents.

This is a guide to the SER’s roles after the construction documents have been issued for construction. It provides guidance on pre-bid and pre-construction activities through the completion of the project. The appendices contain tools and forms to assist the SER in applying this guide to their practice. The project construction delivery system (e.g., design/build, design/bid/build) and for whom the SER works (e.g., owner, architect, general contractor) will influence the approach and the process during the bidding and construction administration phases. It is important to understand that no single method can be defined to accommodate and be totally effective for every construction situation and construction team makeup. Therefore, this guideline includes suggested approaches to the various components that can make up the bidding and construction administration phases.

CASE 962-E – Self-Study Guide for the Performance of Site Visits During Construction Co-authored by ten professional engineers on the CASE National Guidelines Committee, Guidelines for the Performance of Site Visits is a guide intended for the younger engineer but will be useful for engineers of all experience levels. Structural engineers know that site visits are crucial construction phase services that help clarify and interpret the design for the contractor. Site visits are also opportunities to identify construction errors, defects, and design oversights that might otherwise go undetected. Engineers should include adequate construction phase services as a part of their scope of services to ensure the design intent is properly implemented. In 2016, the document was updated with key points to summarize each section, updated references and definitions, and details on current tools for conducting site visits. A companion document is available and was also updated in 2016: CASE Tool 10-1: Site Visit Cards.

CASE 962-G – Guidelines for Performing Project Specific Peer Reviews on Structural Projects Increasing complexity of structural design and code requirements, compressed schedules, and financial pressures are among many factors that have prompted the greater frequency of peer review of structural engineering projects. The peer review of a project by a qualified third party is intended to result in an improved project with less risk to all parties involved, including the engineer, owner, and contractor. Many aspects of the peer review process are important to establish prior to the start of the review to ensure that the desired outcome is achieved.

These items include the specific goals, scope and effort, the required documentation, the qualifications and independence of the peer reviewer, the process for the resolution of differences, the schedule, and the fee. The intention of these guidelines is to increase awareness of such issues, assist in establishing a framework for the review, and improve the process for all interested parties. A companion document is available and was updated in 2019: CASE #7 – An Agreement for Structural Peer Review Services.

You can purchase these and the other Risk Management Tools at www.acec.org/bookstore.

Follow ACEC Coalitions on Twitter – @ACECCoalitions.

FEBRUARY 2020

41

structural FORUM Operational, Redundancy, and Ductility Factors for Bridge Structures

By Roumen V. Mladjov, S.E., P.E.

T

he structural design of buildings and bridges is currently based on the Load and Resistance Factor Design (LRFD) method. The main structural design philosophy is to maintain the factored resistance (the strength of the entire structure and all its elements) above the maximum demand from the worst possible combination of loads on the structure. The ratio of the strength to the demand represents the safety of the structure, where the nominal resistance is reduced by multiplying factors < 1.0, while the loads are increased by multiplying factors >1.0. These multipliers are the safety factors prescribed by the design codes and specifications for both building and bridge structures.

For simplicity, all strength-reducing or loaddemand-increasing factors are called safety factors in this article.

The basic LRFD bridge design equation is: Σ ηi γi Qi < ϕRn, where ϕRn is the factored resistance/strength of the structure, and Σ ηi γi Qi is the factored load combination.

The code safety coefficients in structural analysis and design have worked satisfactorily, ensuring the general safety of building and bridge structures. Over the years, structural design codes have been developed, evolved, and enhanced. Building and bridge structures have their individual specifics with different governing design codes while using the same general philosophies and similar approaches in design.

Historically, the design and construction of building and bridge structures have influenced each other, borrowing structural systems and construction methods. Building codes prescribe importance factors, depending on the building occupancy categories, to increase the demand for more important structures.

Until recently, the bridge design specifications did not differentiate between the bridge’s importance. Now, AASHTO has introduced in its design specifications a new load modifier ηI, the product of three “safety factors”: operational importance ηI, redundancy ηR, and ductility ηD, or (ηi = ηI x ηR x ηD).

For each of these factors, the required upper values are 1.05 maximum for critical or essential bridges and for design having non-redundant and non-ductile elements; a 42 STRUCTURE magazine

lower value of 0.95 is allowed for less important bridges, for design with higher levels of redundancy, and with ductility beyond those required per specifications.

Operational importance applies to the strength and extreme event limit states only.

While the bridge “safety” factors for operational importance, Great Belt East Bridge, Denmark. redundancy, and ductility are from 1.05 to 0.95 or combined are up to a) Importance factor:1.3 to 0.95 based 1.16, the respective ASCE 7 building factors on the amount of average daily traffic are from 1.0 to 1.5 or combined are up to and the importance of the road: 1.95 (1.5 Importance Factor Category IV, 1.3 b) Redundancy factor: 1.0 for 5 or more Redundancy Factor), almost seventy percent elements capable of redistributing loads; 1.1 for 3 such elements; 1.15 higher. for two such elements; 1.25 for a Introducing the load modifier, ηi, was a posisingle element without a “back-up”; tive decision; however, the upper and lower c) Non-ductile structures, elements, and values (1.05 to 0.95) do not correctly repreconnections should not be allowed in sent the significant difference between critical earthquake-prone areas. essential bridges and regular bridges. For example, no difference is considered between The proposed change would improve the bridges carrying a few hundred, or 200,000 to combined value for the ηi load modifier for 300,000 vehicles daily, or for a bridge located bridges varying from 0.95 to 1.63, from the on a critically important road. This approach current value from 0.86 to 1.16. has been criticized by other engineers, like AASHTO may consider a reliability factor Theodore P. Zoli in his article, Operational to be assigned by the Engineer of Record, Importance, Redundancy, & Ductility – Code depending on the reliability of the design, Considerations for AASHTO LRFD. construction, control, and maintenance of Regarding the redundancy, 1.05 is a very low the structure. Such a factor could be between value for a non-redundant bridge structure; 1.25 1.10 (for not completely reliable) and 0.95 would probably better represent the increased (for a very reliable project). risk of using a single or very few members of the In conclusion, bridge design specifications structure without back-up for eventual failure. need to be updated, correcting the combined The reduction to 0.95 for the redundancy factor load modifier ηi based on the discussion above. should be removed as it reduces safety; the use Also, it may be necessary to ensure that state of redundant elements is a requirement.

Departments of Transportation likewise amend Regarding ductility, non-ductile components their specifications to coincide with AASHTO’s and connections should not be allowed for specifications, provided that the state requirebridges in seismic areas, similar to what is ments are equal or more stringent; these required for building structures in California. amended requirements should not use Using safety factors for importance, redun- lower loads or lower safety factors than dancy, and ductility is necessary, but current those provided by AASHTO.■ provisions are not sufficient. It is not acceptable that the current safety of some bridges on Roumen V. Mladjov has more than 55 years essential roads, carrying 200,000 to 300,000 in structural and bridge engineering and vehicles per day, should be less than the safety construction management; his main interests of a two-story building with 30 to 40 occuare structural performance, seismic resistance, pants. Bridge design specification should be efficiency, and economy. (rmladjov@gmail.com) improved as follows: FEBRUARY 2020

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