STRUCTURE magazine | January 2015

A Joint Publication of NCSEA | CASE | SEI

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January 2015 Concrete NCSEA Winter Leadership Forum Coral Gables, Florida January 29 & 30

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January 2015 30

Feature

ridge Hinge reconstruction B in San Francisco

edItorIal

7 the New Year, a time of transitions

By Andrew Rauch, P.E., S.E.

StruCtural reHaBIlItatIoN

24 divine design: renovating and Preserving Historic Houses of Worship, Part 2

By Nathaniel B. Smith, P.E. and

INFoCuS

Milan Vatovec, P.E., Ph.D. INSIgHtS

28 engineering on-the-go StruCtural ForeNSICS

10 Condition assessment of old Stone retaining Walls

By Dan Eschenasy, P.E. CoNStruCtIoN ISSueS

14 Crack Control Measures for tilt-up Concrete Panels

By John Lawson P.E., S.E. and Joe Steinbicker P.E., S.E. Code uPdateS

19 Changes to the 2015 National design Specification (NdS) for Wood Construction

By John “Buddy” Showalter, P.E.,

34

Feature

9 the Challenge of Writing

By Jon A. Schmidt, P.E., SECB

By Ric Maggenti, P.E., Sergio Gomez, P.E. and Roberto Luena, P.E. Projects on aging highways need be done as quickly as possible so as to minimize disruptions to a local economy’s infrastructure. Caltrans maintenance engineers observed the gradual disintegration of hinges on the Southern Freeway Viaduct on Interstate 280 in San Francisco.

Read about the unique scheduling and retrofit procedures developed to ensure the project’s success.

By Nick Murphy, P.E. HIStorIC StruCtureS

46 the Whipple Bowstring truss

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

51 the distinctive ‘Floating’ roof of Jasper Place library

By Derek Ratzlaff, P.Eng

daptive reuse Investigation a of roof Framing

By D. Matthew Stuart, P.E., S.E., SECB Industry City in Brooklyn, New York required an evaluation of the existing roof structures at several buildings of the historic Bush Terminal Complex. The primary purpose was to determine the load-carrying capacity for new “green” roofing systems, solar panel arrays and other adaptive reuse proposals.

39

Feature

.S. Construction u Spending up

By Larry Kahaner Construction spending in the United States rose more than expected in October, logging a 1.1 percent increase, the largest gain since May according to the Department of Commerce. This data suggests some momentum for the fourth quarter of 2014. Amid this backdrop of positive data, many foundations companies are seeing increased work.

StruCtural ForuM

58 the Case for three Significant Figures

By Phillip C. Pierce, P.E.

Bradford K. Douglas, P.E. and Michelle Kam-Biron, S.E., P.E.

On the cover Fast + Epp collaborated with Hughes Condon Marler Architects and Dub Architects to construct Jasper Place Library, a 15,000 square foot replacement of an existing facility. Read more on this project in the Spotlight article on page 51. Photo courtesy of Stephan Pasche.

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

STRUCTURE magazine

5

IN everY ISSue 8 Advertiser Index 45 Resource Guide (Anchor Updates) 52 NCSEA News 54 SEI Structural Columns 56 CASE in Point

January 2015

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Editorial

The new trends, New new techniques Year, and a Time current industry of Transitions issues

By Andrew Rauch, P.E., S.E., LEED AP, CASE Chair

F

irst, I would like to take the opportunity to wish all of you a Happy New Year. I hope this year holds promise for you in your individual careers, for your firms, and for our profession. Second, I would like to extend a thank you and best wishes to Bob Barnett of the Alabama firm of Barnett, Jones, Wilson. Bob has been a fixture on CASE’s Guidelines Committee for as long as I can remember, but is stepping back from his committee work as he moves into retirement.

His down-to-earth approach has helped to keep our practice guidelines grounded in reality. I will miss his wit and friendship during our meetings.

This past fall, I had the opportunity to attend the ACEC Fall Convention in Hawaii, tough duty I know. As part of this conference, I attended the CASE Risk Management Convocation. The Convocation’s three excellent sessions were interspersed among ACEC’s fascinating plenary sessions. The first Convocation session was presented by Brian Stewart of Collins, Collins, Muir & Stewart, James Schwartz of Beazley and Rob Hughes of Ames & Gough. This session topic was on potentially hidden risks in design contracts, showing us the type of language that can creep into your contracts and raise your standard of care without your realizing it. The second session was presented by Dan Buelow of Willis A&E. This session provided the five primary areas of firm risk management. The information, and the case studies that went along with it, provided a terrific introduction to risk management for those new to it and a good refresher for those already more familiar with the concepts. The third session was presented by Karen Erger of Lockton Cos. and Eric Singer of Ice Miller LLP. This session presented some of the enduring, long-standing risks of the engineering profession along with several new, emerging risks.

Their lighthearted style always makes the sometimes dry topic of contracts and risk management more interesting.

On the day before the convocation, I was able to attend ACEC’s small firm roundtable. This session is an open discussion of topics generated from the attendees who are CEO’s or other leaders from firms with fewer than 50 employees. I attend whenever I can, as I am always able to pick up nuggets of information and wisdom. These sessions, and the more informal ones that occur outside of the sessions and during our committee meetings, are one of my primary reasons for becoming and remaining actively involved in CASE. The topic of most interest to me at this session was on firm ownership transition. It was generated by several different individuals from the leader of a multi-generational firm, from a second generation firm and from solely-owned first generation firms. Others in attendance offered ideas and practices on how firms are valued.

Some are valued based on revenue; some are valued based on a combination of profit and asset value. One firm prices its stock at par value only using ownership as a means to distribute earnings.

Other firms use an ESOP, either full or partial, to accomplish this goal.

A second theme in this discussion that resonated with the attendees was the differing approach of the next generation, the STRUCTURE magazine

Gen-X’s and millennials, toward firm ownership. I know that I am generalizing, but the next generation of engineers does not put as much value on firm ownership as do the retiring baby boomer owners. This attitude, together with their tendency to move around during their careers, makes identifying these future leaders and potential owners much more difficult. When they have been identified, retaining them becomes the next challenge.

Rather than complaining about these circumstances, as leaders we need to accept these challenges and find ways to capitalize on them for our firms.

Based on the experience of our firm and on various presentations that I have attended on this topic, work-life balance and having an opportunity to grow and learn are important factors for these upcoming leaders. Work-life balance is an aspect of your firm culture that may need to be modified if it is not appropriate. An atmosphere of continual learning will help with the second factor.

CASE Tool 5-2 provides ideas for planning and monitoring the growth of young engineers. Although it is geared for those initial years of engineering practice, it can be adapted and modified to continue the growth of all the members of your firms.

If your firm has already identified your next generation of leaders and you have this transition plan in place, congratulations. If you are one who has the process underway, I wish you success in completing and implementing your plan. If you have not begun the process, my hope would be for you to understand that it requires a time commitment and encourage you to get started before it is too late.▪ Andrew Rauch, P.E., S.E., LEED AP, is a principal with BKBM Engineers in Minneapolis, MN. He is the current chair of the CASE Executive Committee. He can be reached at arauch@bkbm.com.

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January 2015

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

EDITORIAL STAFF Executive Editor Jeanne Vogelzang, JD, CAE execdir@ncsea.com Editor Christine M. Sloat, P.E. publisher@STRUCTUREmag.org Associate Editor Nikki Alger publisher@STRUCTUREmag.org Graphic Designer Rob Fullmer graphics@STRUCTUREmag.org Web Developer William Radig webmaster@STRUCTUREmag.org

EDITORIAL BOARD Chair Jon A. Schmidt, P.E., SECB Burns & McDonnell, Kansas City, MO chair@structuremag.org Craig E. Barnes, P.E., SECB CBI Consulting, Inc., Boston, MA John A. Dal Pino, S.E. Degenkolb Engineers, San Francisco, CA Mark W. Holmberg, P.E. Heath & Lineback Engineers, Inc., Marietta, GA Dilip Khatri, Ph.D., S.E. Khatri International Inc., Pasadena, CA Roger A. LaBoube, Ph.D., P.E. CCFSS, Rolla, MO Brian J. Leshko, P.E. HDR Engineering, Inc., Pittsburgh, PA Brian W. Miller Davis, CA Evans Mountzouris, P.E. The DiSalvo Engineering Group, Ridgefield, CT

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Greg Schindler, P.E., S.E. KPFF Consulting Engineers, Seattle, WA Stephen P. Schneider, Ph.D., P.E., S.E. BergerABAM, Vancouver, WA John “Buddy” Showalter, P.E. American Wood Council, Leesburg, VA Amy Trygestad, P.E. Chase Engineering, LLC, New Prague, MN

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January 2015

C3 Ink, Publishers A Division of Copper Creek Companies, Inc. 148 Vine St., Reedsburg WI 53959 Phone 608-524-1397 Fax 608-524-4432 publisher@structuremag.org January 2015, Volume 22, Number 1 ISSN 1536-4283. Publications Agreement No. 40675118.

Owned by the National Council of Structural Engineers Associations and published in cooperation with CASE and SEI monthly by C3 Ink. The publication is distributed free of charge to members of NCSEA, CASE and SEI; the non-member subscription rate is $75/yr domestic; $40/yr student; $90/yr Canada; $60/yr Canadian student; $135/yr foreign; $90/yr foreign student.

For change of address or duplicate copies, contact your member organization(s) or email subscriptions@STRUCTUREmag.org. Note that if you do not notify your member organization, your address will revert back with their next database submittal. Any opinions expressed in STRUCTURE magazine are those of the author(s) and do not necessarily reflect the views of NCSEA, CASE, SEI, C3 Ink, or the STRUCTURE Editorial Board.

STRUCTURE® is a registered trademark of National Council of Structural Engineers Associations (NCSEA). Articles may not be reproduced in whole or in part without the written permission of the publisher.

InFocus

The new trends, Challenge new techniques and of current Writing industry issues

By Jon A. Schmidt, P.E., SECB

W

riting is hard work for most people, myself included.

Mozart supposedly finished entire musical compositions in his head before committing any of the notes to paper, but for almost everyone else, our minds simply do not work that way. As David Hare put it, “The act of writing is the act of discovering what you believe.” I have certainly found that to be true when preparing these columns over the years.

I generally start by sorting through a particular jumble of thoughts, and then try to reorganize them in a way that will (hopefully) make sense to someone else. I know that I have not always – perhaps not even often – succeeded in that regard. This magazine’s audience of practicing structural engineers is not known for its philosophical bent, as I have acknowledged (and sought to change) in papers and presentations with titles like “Engineers Don’t Think Enough About Engineering.”

Perhaps I am hopelessly “kicking against the goads” by continuing to offer up rather dense tomes that advocate a different (one might say foreign) perspective on our profession – exploring not only what we do, but also how we do it and why it matters. The general dearth of feedback from readers, even in the days when there was a dedicated “Your Turn” page on the website for that very purpose, suggests that this might be the case.

At the same time, I do occasionally receive encouragement to continue doing what I have been doing, and not just from my fellow members of the Editorial Board and the SEI Engineering Philosophy Committee. It seems like, whenever I attend a conference, at least a couple of people come up to me and say that they enjoy my columns, even while not necessarily understanding them. They probably mean this as a compliment, but I cannot help feeling a twinge of frustration.

Such a comment is sometimes accompanied by the suggestion that I should “write a book about all of this.” Maybe the underlying assumption is that the limitation to a single magazine page forces me to boil everything down to an extent that precludes careful explanation, and not having that constraint would free me to lay things out more clearly. My honest response, though, is that I find the notion of writing an entire book very intimidating.

For one thing, I know how many hours I spend grinding out a 950-word piece every couple of months; so it feels like it would take me forever to generate 60,000 or more words to fill 150 or more pages. In addition, I simply consider myself to be far more adept at condensing and summarizing than at expanding and elaborating; why take a whole chapter to make a point when I can capture its essence in a paragraph or two?

I wonder, though, if I am falling into a common trap that authors Chip and Dan Heath call “the Curse of Knowledge” in their 2007 bestseller, Made to Stick. Back when I was in college, I tried to help my girlfriend (now wife) with her calculus homework, but I was consistently unsuccessful because – according to her – I kept “skipping steps” that were obvious to me, but evidently not apparent to her. Have I been guilty of making the same mistake here?

The Heath brothers carefully investigated what causes some ideas to thrive and others to fade away. Their goal was to identify

STRUCTURE magazine

what steps we can take to make our ideas more “sticky” – that is, more likely to be remembered and acted upon by others.

The Curse of Knowledge inhibits this because, “Once we know something, we find it hard to imagine what it was like not to know it.” The book lays out six specific characteristics of “sticky” ideas, which together form the slightly misspelled acronym, SUCCES: • Simple – prioritize to determine the core of your message, and then express it in a compact way by linking it to something that is already familiar.

• Unexpected – grab attention with your message by breaking a pattern, and then keep it by offering meaningful insight and sparking further curiosity.

• Concrete – employ sensory language in your message by painting mental pictures that relate to the real world and trigger multiple types of memory.

• Credible – confirm your message by citing expertise or experience (yours, others’, the audience’s) and including human-scale statistics or vivid details.

• Emotional – associate your message with something that people already care about by appealing to self-interest or group identity.

• Stories – prompt action in response to your message by providing simulation (how to act) and inspiration (why to act).

The 2010 movie Inception portrays how these ingredients could facilitate planting an idea in someone else’s head without the other person realizing it. Although dreams take place entirely in the mind, they seem quite concrete while we are dreaming, and the strategy is to create a story with unexpected elements that will surprise the subject in a certain way. The characters explicitly discuss the importance of finding “the simplest version of the idea” and tapping into (preferably positive) emotions. One of them specializes in impersonating someone who already has credibility with the target.

The film made me wonder if it would be possible to “perform inception” without dream-sharing technology, because I want to be more successful in conveying and spreading my ideas about engineering and philosophy. That led me to the Heath brothers, and they revealed the problem: like most engineers and philosophers, I am quite comfortable operating in the realm of the complex, routine, abstract, and analytical. Breaking out of this default mode of thought requires an alternative, which I will discuss next time.▪ Jon A. Schmidt, P.E., SECB (chair@STRUCTUREmag.org), is an associate structural engineer at Burns & McDonnell in Kansas City, Missouri. He chairs the STRUCTURE magazine Editorial Board and the SEI Engineering Philosophy Committee, and shares occasional thoughts at twitter.com/JonAlanSchmidt.

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January 2015

Structural ForenSicS investigating structures and their components

T

he New York City stock of retaining walls is dominated by concrete and masonry walls. The older stock, dating from late 1800s and early 1900s, consists of stone masonry walls. Originally, these soil retaining structures were mostly commissioned and supervised by public works, parks, railway or highway administrations. In the early 1900s, under pressure from strong residential needs, the city started to open streets in hilly areas that previously had not been considered suitable for construction. Private development ensued and developers began to erect stone retaining walls to meet street lines or to create terraces around their properties.

A recent New York City local law requires periodic inspection of walls that are taller than ten feet and that front a right of way. The professional performing the condition assessment of old stone walls needs to be capable of recognizing symptoms of distress while being aware of the regulatory and design criteria as well as of the construction methods that formed the retaining wall practice at the time these walls were erected.

This article provides a general overview of the issues related to the assessment of old stone retaining walls existing in New York City. Most of the symptoms of deterioration discussed were observed during the New York City Building Department’s inspections and filtered through the experience of several forensic collapse investigations (See Figures 2, 5 and 6, see page 12).

Condition Assessment of Old Stone Retaining Walls

By Dan Eschenasy, P.E., F.SEI

Construction Dan Eschenasy, P.E., F.SEI, is the New York City Buildings Department Chief Structural Engineer. He is a member of the ASCE Structural Assessment of Buildings Committee.

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

Modern engineering systems classify old masonry walls as “gravity walls”, as their stability is provided by their weight. At the time they were built, the classification was based on the type of stone used for their exposed face – ashlar and rough.

Ashlar, built with stone precisely cut, represented the higher “class” of wall construction in contrast to the rough (or rubble) walls that were built with stone that was not cut or not cut at right angles.

The retaining walls were usually erected in lifts and started with the regular masonry face behind which lesser quality stone was deposited or dumped. Like in any multi-wythe bearing walls, headers (through-stones) were necessary to connect the vertical wythes. The mason’s skill consisted of selecting each stone so that it fit with the adjoining stones. Walls built without mortar or any other binding layer are called dry walls. In the absence of mortar, the gaps between stones were filled with smaller stones called pins. The pins were also used to hold the larger stones in desired positions. High quality stone dry wall construction possessed significant

10 January 2015

stone-to-stone contact. Some stone walls, most likely built after World War I, were stabilized with anchor rods and, as such, are not gravity walls. The importance of water drainage and of the type and mode of backfill has been recognized since the earlier periods.

Building Code Regulation The first city building code instructions involved only basement walls that were intended to retain soil. The first ordinance to cover any structure retaining soil was issued in 1915 and was incorporated in the 1916 code. Retaining walls were required to be “so designed that in resisting the pressures to which they are subjected, including any water pressure that may exist, the working stresses of the materials shall not be exceeded, the soil shall not be overloaded and the stability of the wall shall be insured.”

This text remained until 1938, when the code was changed to provide engineering design instructions only for basement walls.

The first explicit factor of safety of 1.5 for overturning and sliding was set in the 1968 Code, matching the widely recognized Design Manual: NAVFAC DM-2 Dec. 1967. This factor of safety value has remained in the code since. In 1995, the code was amended to include seismic loads on retaining walls.

Design Criteria Because original construction records rarely exist, it is unlikely that an engineer performing a condition assessment of a particular wall would know which design method was used. Of course, the fact that a wall has survived decades is proof of the reliability of the original design, but sometimes, without an in-depth analysis, it may be difficult to establish whether an observed deterioration is an indication that the structure is reaching the limits of its safe life.

Around 1890, J. Trautwine, arguing that “experience, rather than theory must be our guide”, published empirical guides for proportioning retaining walls. These guides seem to have been widely followed.

Trying to make sense of the numerous theories of retaining wall design in his Treatise of Masonry Construction (1899), Ira Baker found only three reliable theories (Coulomb’s, Rankine’s and Weyrauch’s theories) and two empirical rules (English by Benjamin Baker and Trautwine’s rules).

Ira Baker enumerates the following “methods of failure”: ”(1) By revolving about the front of any horizontal joint, or (2) by sliding on the plane of any horizontal joint, or (3) by the bulging of the body of masonry.” Developed around the same period, the classification of failures into overturning, crushing and sliding was more helpful, as it

retaining walls started to be built around World War I. Not uncommon in New York City are walls with stone or brick veneer with concrete backup stem walls. They were built after 1940 and are assessed as concrete (flexible) walls.

Visual Assessment

Figure 1. Crack in rubble wall.

could be used as a guide to design. Friction and compressive strength of the wall material or of the underlying soil could be evaluated and compared with limits determined by testing.

By and large, these modes of failure are still basic considerations in modern gravity wall designs. General soil slope stability became a recognized mode of failure after 1920.

The 1920 G. Paaswell’s overview of contemporary design methods shows that most had embraced Rankine’s and Coulomb’s theories.

Paaswell reports that the calculation methods produced various overturning factors of safety, all higher than 2.5. In his view, the attention paid to overturning was exaggerated since most retaining walls collapsed due to underlying soil failures and rarely in overturning. He favored graphic design methods that better predicted pressures on soil, as they forced the resultant to be in the middle third of the base.

In short, most of New York’s stone masonry walls were erected during the period when designs evolved from empirical methods to quasi-modern design theories. Concrete

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January 2015

Figure 3. Irregular alignment at top of wall.

reached, but again, this might be disturbed by subsequent events (e.g., high rainy seasons) capable of increasing the pressure.

Outward rotation or movement of a wall has associated signs of distress that include sink holes and tension cracks at or around the top of the wall. Sometimes sink holes may only indicate erosion of the retained soil. At the bottom of the wall, one might observe soil swelling and sloping towards the wall. For long stretching walls, observation of the alignment at the top of the wall can indicate differential movement of wall segments. It might also help distinguish walls built with batter from wall segments that moved (Figure 3).

Incipient sliding failure at the base may be preceded by swelling of soil at the bottom of the wall. In some cases, there is a separation of soil at the top of the wall. Sliding of portions of the wall along intermediate planes can lead to outward deformation of

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Figure 2. Retaining wall stabilized with rakers after collapse. Note lean of wall.

Intended for the National Park Service, the Retaining Wall Inventory and Condition Assessment Program ( WIP) recommends that assessments of old walls be guided by visual observations and also take into consideration determinations whether the wall “is consistent with other structures of its type and period of construction exhibiting established construction workmanship and good performance,” Casting some doubts on the effectiveness of visual inspections Y. C. Chan reports, in his Study of Old Masonry Retaining Walls in Hong Kong, several cases of walls that collapsed without forewarning signs. This is not New York City’s forensic experience, but one can envision cases where walls in good condition were overwhelmed by newly applied forces that exceeded the original design.

Any aging stone facade may show signs of deterioration, i.e. delamination, peeling, erosion, loss of mortar, unit cracking, etc.

A visual assessment of a stone retaining wall needs to differentiate between such symptoms of aging and those that indicate the possibility of a more severe failure or accident. For instance, some cracks, commonly found in the vicinity of corners, are just the result of deformations due to thermal movement. Such expansion cracks, even when they completely separate the wall into two segments, might not affect the wall’s stability, as each segment may remain capable of resisting the out of plane forces acting upon it (Figure 1).

Outward lean of a wall is a significant symptom presaging collapse (Figure 2). It may be caused by insufficient or deteriorating strength or by the failure of the soil underlying the toe. In the absence of original drawings, it is difficult to ascertain whether the present orientation of the wall face matches the original intended geometry. (e.g., did the wall move from an original batter?). Over a long period of time and as a result of intermittent load increases (e.g., high rainy seasons and icing pressures at the top) and simultaneous reduction of friction, the wall might have slowly moved from the original vertical or battered position, thus reducing the original factor of safety. It is conceivable that the outward displacement of a wall might decrease the pressure of the retained soil (i.e. from at rest pressure to active pressure). A new equilibrium is then

Figure 4. Bulging wall.

the top of the wall or bulging at the lower parts of the wall. Sliding of the top of the wall may lead to collapse of this top portion (Figure 4 ).

When bulging is local, one could assume that it is due to some construction deficiency like an improperly pinned or placed stone. But bulging on larger areas is a sign of crushing and sliding due to stresses concentrating towards the outside edge of the wall.

Bulging can also be caused by insufficient ties between wythes.

Even when the aspect of the outside face is satisfactory, there remains significant uncertainty as to the method of construction used for each particular wall (Figure 5).

Increase in Load Unlike other structures, a retaining wall is exposed to most of the design loads as soon as it is built. One could assume that, over the long period since a wall’s erection, the high and continuous loads have already produced the collapse of poorly constructed or designed walls. Assessment of indications of changes potentially leading to an increase in loading conditions is essential.

Change in grading, demolition or construction of a nearby building can be significant sources of new or increased loading (e.g., new pressures on soil or changes in water flow patterns.)

An effective assessment needs to include the entire system of rain water management, as water accumulation behind the wall can produce a significant load increase. Many wall collapses have been associated with heavy rainfalls. Usually, when provided with drains and weep holes, walls need not be designed to resist water pressure. But the drains can deteriorate or get clogged. Fines transported from elsewhere might reduce the drainage

Figure 5. A visual inspection prior to collapse might not have detected that the wall was only 2 feet deep.

capacity of the crushed stone layer intended to allow water circulation. New grading of areas, or of streets at tops of walls, may change the distribution of rain water.

Significant vegetation growth on the face of a mortared stone wall could be a sign of continuous water presence due to a lack of sufficient drainage. Water leaking through joints or cracks is a sign of a drainage system malfunction.

Dry stone walls generally allow water to circulate, except for cases when subsequent repairs added mortar to the face of the wall (Figure 6 ). Ice formation or tree roots might create “wedges” that could lead to some local wall deterioration.

Detailed Assessment The condition assessment needs to correlate the various symptoms observed and to integrate them into a final evaluation that indicates the safety risk, if any, posed by the retaining wall in its totality or posed by individual elements. In some cases, uncertainty about the wall condition will require a detailed engineering investigation. Exploratory probes and tests can reduce by a significant amount the uncertainty regarding data to be used in calculations (wall profile, position and inclination of back side, characteristics of backfill, specific weight of the wall itself, engineering properties of mortar, depth of wall foundation and capacity of underlying material, etc.).

Often, the confidence of the assessment can be improved by the use of a sensitivity analysis, a method that helps establish by what

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January 2015

degree an uncertain result (e.g. overturning factor of safety) is dependent of the variation of an uncertain input (e.g. weight of wall, backfill density or soil friction, etc.)

Evaluation The large number of uncertainties that make assessments of old stone walls difficult should not necessarily lead to the conclusion that these walls are inherently unsafe. The evaluation should take into consideration all observations of individual symptoms, and consider their cumulative effects as well as their relationship to each other and to the wall’s structure. In some cases, the engineering opinion might need to be supported by probes and engineering calculations.▪

Figure 6. Collapsed dry wall. Repair pointing at the base, intended to keep pins in place, might have contributed to collapse.

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ConstruCtion issues discussion of construction issues and techniques

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hen it comes to enclosing large building volumes, it is hard to beat tilt-up concrete construction for economy and durability.

Long considered the mainstay for warehouses and big-box retail, the tilt-up method is now frequently employed for commercial projects, churches, schools and Class A office buildings nationwide. With newer types of occupancies driving attention to aesthetics higher and higher, the importance of minimizing concrete cracking in the site-cast precast wall panels is greater than ever.

Tilt-up concrete construction incorporates concrete wall panels that are formed, cast and cured on a ground supported slab at the building site and then tilted into place, one large panel at a time. The individual wall panels are erected around the building’s perimeter, separated by vertical joints. Single story occupancies are still most common; however, many buildings are now multiple stories. While many of the features of tilt-up panel construction tend to reduce the potential for developing cracks when compared to conventional concrete construction, the unique method of how the buildings are constructed still requires some special considerations for controlling cracking. The lifting and setting of wall panels, as well as the effects of restrained drying shrinkage, are important items to address to minimize potential wall cracking.

Crack Control Measures for Tilt-Up Concrete Panels

By John Lawson P.E., S.E. and Joe Steinbicker P.E., S.E.

Construction Related Cracking John Lawson, P.E., S.E. (jwlawson@calpoly.edu), is Associate Professor in Architectural Engineering at California Polytechnic State University, San Luis Obispo.

Joe Steinbicker, P.E., S.E. (joes@ssa-engineers.com), is a charter member and past chairman of ACI Committee 551, Tilt-Up Concrete Construction. He is also a founding member of the Tilt-Up Concrete Association and past member of their Board of Directors.

In some respects, the concrete wall panels experience the greatest potential for cracking as they are being tilted from horizontal to vertical while being erected. As the panel is lifted from the casting slab, over 1g of force can develop normal to the wall’s surface due to dynamic forces or bonding to the casting slab. These bond forces can develop from an inadequate application of the bond breaker coating on the casting slab, or excessive rain water left standing in the panel openings and reveals without an adequate side draft on at least one edge. As a precaution, the bond breaker application should always be checked just prior to casting the panels. Excessive bending stresses can result in horizontal or vertical cracks aligned at architectural reveals or edges of openings. However, with the use of adequate safety factors, properly located lift-points and appropriate rigging, the out-of-plane bending moments generated during lifting can usually be reduced to acceptable levels to minimize the potential for cracking. If the panel can’t be lifted with an adequate factor of safety, additional measures can be employed as presented later in this article.

14 January 2015

To successfully lift the panels for most of the tilt-up projects designed and built today, the use of sophisticated computer software to analyze the stresses generated in the panels during lifting is required. A specialty lifting engineer, often associated with the tilt-up accessory vendor, who has the required expertise and experience, most often provides this service. Typically, the panel designer will not provide the analysis and design required for lifting the panels. However a general understanding of the lift engineering process will help in designing panels that can be erected economically with minimum potential for cracking during construction.

Ideally, the tilt-up panels can be erected without developing any cracks during the lifting process.

Therefore, the panels are typically designed using only the allowable flexural tension strength of the uncracked panel section without relying on the steel reinforcement. The calculated bending stresses within the panel are kept low enough so that cracking should not occur. The minimum concrete flexural strength required prior to lifting the panels is specified by the specialty lifting engineer to provide an adequate factor of safety of about 1.67 against cracking. For most projects, a minimum compressive strength of 2,500 psi with a corresponding allowable flexural stress of 300 psi (typically calculated as 6 √f'c) is specified by the specialty lifting engineer and is considered the minimum requirement prior to lifting the panels.

If the calculated flexural tension stress exceeds the specified minimum allowable due to large panel openings or reduced sections at reveals or recesses, a higher strength concrete can be specified for those panels to increase the allowable flexural stress in order to maintain an adequate factor of safety against cracking. When the concrete strength is increased, the panel reinforcing should be checked to verify that φMn ≥ Mcr is still satisfied as required by ACI 318. Another approach often used is to design the lifting stresses closer to the ultimate plain concrete flexural stress (sometimes calculated as high as 10 √f'c) with less margin against cracking, and provide redundant steel reinforcement to resist the entire calculated bending moment should cracking occur. Many times, when the as-designed structural reinforcing is accounted for, no or only a few extra reinforcing bars are necessary to be added to the engineered wall design. When reinforcing is added for lifting, the section should be checked to verify that it is not over-reinforced, creating a compression controlled critical section.

In some panels with extremely large or unusual openings, external strong-backs will have to be added temporarily to the panel to resist the calculated bending moments and stiffen the panel sufficiently in order to keep the concrete flexural stresses below the estimated cracking strength of the section. The use of strong-backs add time and

Figure 2. Grout setting pads at panel joints with an inactive shim at the panel center.

Figure 1. Panel to panel connector plate designed with bolts and slotted holes to accommodate panel shrinkage and temperature movements, inadvertently welded on both sides of the joint.

expense to the project. Many times slightly increasing the thickness of the panels can eliminate the need for strong-backs and actually reduce the cost of the project. Simply adding reinforcing steel has limited effectiveness, especially because the steel remains primarily dormant until the concrete cracks.

Drying Shrinkage Cracking The Engineer-of-Record (EOR) for a building typically has limited involvement in the means and methods of rigging and lifting a panel during construction, and the related cracking that could occur. However, the EOR often has more control to address potential cracks associated with concrete drying shrinkage.

Cracking in tilt-up wall panels can occur when excessive restraint prevents the movement from horizontal drying shrinkage.

Drying shrinkage naturally occurs as water exits the concrete material, and can become a significant consideration depending upon several factors. Fortunately, vertical panel joints that are free of panel-to-panel connections inherently provide strain relief for the horizontal concrete shrinkage; however, diaphragm chord connections at the roof and floors, and foundation and slab connections, create unintentional restraint. Greater panel widths have greater horizontal shrinkage potential, so limiting widths where possible is recommended. Panel widths between 20 and 30 feet are most common.

When welded panel-to-panel connections occur, isolated embedded plates and anchors near the panel joints could suffer a concrete

breakout failure unless sufficient reinforcing steel is utilized to develop the resulting forces deeper into the concrete. Figure 1 illustrates a panel-to-panel connection with bolts in horizontal slotted holes to accommodate the horizontal movement; however, the plate was inadvertently welded on both sides, creating horizontal restraint. Tilt-up designers often avoid welding a large series of panels together across the panel joint to minimize this problem. Roof and floor chord connections are an exception.

At the roof and floor chords, welded connections are common, but the use of horizontally slotted bolt holes near the panel joints in rolled steel ledger sections minimizes the restraint to horizontal shrinkage near the vulnerable panel joint edge. Additionally, some engineers specify a delay in welding the panels together across the joint until roof erection is well underway to allow a larger percentage of the ultimate horizontal shrinkage to occur, and allow the concrete strength to increase, prior to welded restraint. The best solution is to keep restrained panel-to-panel connections well away from panel joints.

One of the more aggravating cracking patterns is caused by base restraint due to long term drying shrinkage. When the wall panels are erected, they are normally placed on two 1-inch to 2-inch thick grout setting pads placed on the foundation, and the frictional restraint at this bearing condition may have significant

Figure 3. Potential crack pattern associated with setting pads and other base restraint conditions.

resistance to the horizontal shrinkage (Figure 2). The resulting tensile forces can combine with the vertical shear forces to result in a cracking pattern of several radiating cracks in the lower quarter of the panel’s height (Figures 3 and 4 , see page 16). Ideally these setting pads are hard plastic shim packs instead of grout pads, thus minimizing the frictional restraint to horizontal in-plane shrinkage. Situations where contractors use a single grout setting pad at the panel joints (Figure 2) have been especially problematic. For contractors who insist on using grout setting pads, the potential for

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STRUCTURE magazine

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January 2015

be an appropriate course of action to consider, as is demonstrated in the following example:

Figure 4. Cracking associated with base restraint.

developing these cracks can be minimized by providing independent setting pads away from the panel joint instead of a single common setting pad, thus reducing the amount of shrinkage strain between the friction restraints as well as reducing the interacting vertical shear at the pad support.

Similar restraint issues can occur after the joint below the panel is grouted, or if panels are immediately connected to foundations and/or the slab-on-grade. By delaying connections to the footing or slab and allowing a larger percentage of the ultimate drying shrinkage to occur, while also allowing the concrete strength to increase, the likelihood of developing these cracks is reduced.

Many of the solutions discussed so far deal with minimizing the restraint or resisting it with reinforcing steel. It is also helpful to encourage much of the drying shrinkage to occur prior to any connection or restraint forming. For example, extending the time between when the concrete panel is cast and lifting it into place allows the concrete’s tensile strength to increase and allows a larger portion of the ultimate shrinkage to occur.

Typically panels are lifted within two weeks of casting. Use of proper curing techniques also allows a rise in concrete tensile strength while slowing down drying shrinkage.

The amount of shrinkage expected in the concrete can also be reduced by controlling the amount of water necessary in the mix, and/or increasing the amount of coarse aggregate without causing honeycombing or voids, and/or other techniques such as shrinkage reducing admixtures.

It is not practical to expect all restraint to be eliminated, and it may be prudent to provide additional reinforcing to limit crack widths.

In many parts of North America, the tilt-up wall panels are placed on cementitious grout pads on top of the foundation, with the resulting joint subsequently grouted, and the only positive connection occurring at the floor slab at some later date during construction. In this situation, providing enough reinforcing steel to withstand the calculated restraint force may

Panel thickness = 8 inches Service gravity load acting at base of panel, PTOTAL = 110 kips Factored gravity load acting at base of panel Pu TOTAL = 150 kips Factored gravity load acting on each grout pad support Pu = 0.5Pu TOTAL = 75 kips Estimated coefficient of friction between panel and pad µ = 0.6 (ACI 318-11 Section 11.6.4.3) Maximum horizontal self-straining shrinkage force Tu = µPu = 0.6(75 kips) = 45 kips Recommended Grade 60 reinforcing steel area: As =(45 kips)/(0.9(60 ksi)) = 0.83 in2; Use (3) #5 horizontal bars at base of wall (As = 0.93in2) Service load steel stress, fs = (110/2) 0.6 / 0.93 = 35.5 ksi < 40 ksi (ok) Check the maximum clear cover cc on reinforcing provided, per ACI 318-11 Section 10.6.4: s = 15(40,000/35,500) – 2.5 cc with s = panel thickness = 8 inches and solving for maximum cc, where cc is the distance from the bottom of the panel to the surface of the reinforcement. cc = (15(40,000/35,500) – 8)/2.5 = 3.6 inches Place the first bar at 3 inches from bottom of panel; cc provided = (3 – 0.625/2) = 2.7 inches < 3.6 inches (ok) Situations where additional restraint is present, such as panel to footing connections and connections to the floor slab not delayed sufficiently, will have higher self-straining loads Tu and can be addressed in a similar fashion.

Well above the panel’s base, diagonal cracks emanating from the corners of window or door openings can occur (Figure 5) due to

Figure 6. Diagonal corner bars to control cracking.

stress concentrations from long term drying shrinkage at these re-entrant corners. The use of two No. 5 x 4-foot reinforcing bars centered diagonally at the opening corners in addition to the No. 5 bars required by ACI 318-11 Section 14.3.7 (Figure 6) have been successful, keeping the crack size reasonably tight.

Conclusion In closing, the nature of tilt-up concrete construction using individual panels with largely unrestrained panel joints is a great asset to controlling cracking. With greater performance demands, driven by developers and owners, more and more effort is placed on controlling all cracking potential in tilt-up panels.

Because the engineer’s panel design significantly affects a tilt-up project’s constructability, best practices are when the building’s design engineer and contractor’s lifting engineer freely communicate about the difficult portions of the project before construction commences.

Whether a simple warehouse or a five-story class A office building, understanding the mechanisms that lead to possible cracks and addressing them at both the design level and construction level will be of great benefit to a successful finished project.▪

Additional Resources

Figure 5. Potential corner cracks at wall penetrations from drying shrinkage.

STRUCTURE magazine

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January 2015

Engineering Tilt-Up, Timothy Mays & Joe Steinbicker, Tilt-Up Concrete Association, 2013.

The Construction of Tilt-Up, the Tilt-Up Concrete Association, 2011.

Design Guide for Tilt-Up Concrete Structures (ACI 551.2R-10), American Concrete Institute, 2010.

Tilt-Up Concrete Construction Guide (ACI 551.1R-05), American Concrete Institute, 2005.

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he 2015 Edition of the National Design Specification® (NDS®) for Wood Construction was recently published.

The updated standard designated ANSI/AWC NDS-2015 was approved as an ANSI American National Standard on September 30, 2014 (Figure 1). The 2015 NDS was developed by the American Wood Council’s (AWC) Wood Design Standards Committee and is referenced in the 2015 International Building Code (IBC).

Primary changes to the 2015 NDS are listed here, and major topics are subsequently covered in more detail: • Incorporation of cross-laminated timber (CLT) in several chapters of the NDS, including a new product chapter specific to CLT • Addition of terminology for laminated strand lumber and oriented strand lumber • Clarification that withdrawal design values for lag screws excludes the length of the tapered tip • Inclusion of char rates for CLT and structural composite lumber • Relocation of reference to Special Design Provisions for Wind and Seismic (SDPWS)

Cross-Laminated Timber The primary change to the 2015 NDS is incorporation of design provisions for CLT. To keep CLT with other product chapters (4-9), Chapter 10 is renamed Cross-Laminated Timber and each subsequent chapter is renumbered accordingly. The one-sentence reference to SDPWS in 2012 NDS Chapter 14 was moved to Section 1.1.1.4, which allows Chapters 15 and 16 to remain unchanged.

In NDS Chapter 3, a time dependent deformation (creep) factor for design of CLT was added.

The factor of 2.0 is associated with use in dry service conditions and is consistent with the factor of 2.0 for wood structural panels used in dry service conditions. For column design, CLT is associated with a “c” factor equal to 0.9 for calculation of the column stability factor, CP, consistent with glulam.

The new CLT Chapter 10 is consistent with other product chapters in the NDS (Figure 2) but most closely modeled after Chapter 9 for wood structural panels. The applicable product standard for CLT is ANSI/APA PRG 320 Standard for Performance-Rated Cross-Laminated Timber, and applicable design values are to be obtained from manufacturer’s literature or code evaluation report.

Connection provisions were revised to accommodate CLT in Chapter 12, Dowel-Type Fasteners.

A new section applicable for lag screw withdrawal from CLT’s narrow edge (top, bottom, left or right edge) was added. For lag screws loaded in withdrawal from the narrow edge, the end grain factor,

Code Updates code developments and announcements

Figure 1. The 2015 NDS is now available and is referenced in the 2015 IBC.

Ceg = 0.75, is applicable regardless of actual grain orientation. While the Ceg factor is normally applied only to end grain applications in other wood products, application to all grain orientations in narrow edges of CLT is intended to conservatively account for the mix of end grain and side grain in the narrow edge of a CLT panel where the minimum edge distance requirements for lag screws cannot be maintained (as opposed to small diameter nails and wood screws).

New sections applicable for wood screw and nail withdrawal from end grain of CLT were added.

The approach of not recognizing wood screw or nail withdrawal from end grain of CLT is consistent with existing provisions for wood screws and nails in end grain of other wood products. The Ceg = 0.0 factor is added to clarify that there is no design strength associated with such applications.

New sections were added to address determination of dowel bearing strengths for fasteners installed in CLT. For fasteners installed in the panel face, dowel bearing strength is based on direction of loading with respect to the grain orientation of the CLT ply at the shear plane.

Where the loading direction is parallel to the grain at the shear plane, a reduced bearing length approach is used to account for the effect of reduced bearing strengths in perpendicular to grain orientations in adjacent layers. For fasteners installed in the narrow edge, dowel bearing strength perpendicular to grain, Fe, is the applicable bearing strength where fastener diameter, D ≥ ¼ inch, and is intended to account for: 1) presence of end grain bearing in the connection, and 2) end distance, edge distance,

STRUCTURE magazine

Changes to the 2015 National Design Specification (NDS) for Wood Construction

19

By John “Buddy” Showalter, P.E., Bradford K. Douglas, P.E. and Michelle Kam-Biron, S.E., P.E.

John “Buddy” Showalter, P.E. is Vice President of Technology Transfer, Bradford K. Douglas, P.E. is Vice President of Engineering, and Michelle KamBiron, P.E., S.E. is Director of Education with the American Wood Council. Contact Mr. Showalter (bshowalter@awc.org) with questions.

Figure 2. Adjustment factor table excerpted from 2015 NDS new Chapter 10 Cross-Laminated Timber.

and spacing of fasteners that would not otherwise comply with NDS provisions for placement for D ≥ ¼ inch if applied to individual laminations of a CLT panel. For example, if the CLT panel is comprised of three 1½-inch thick laminations, the total thickness would be 4½ inches. Meeting edge distance requirements for 1½-inch laminations might not be possible. For fasteners with D < ¼ inch, a single value of Fe is the applicable bearing strength.

Reduced bearing lengths are used to account for perpendicular grain orientations in crossing laminations where fasteners are installed in the panel face, penetrate multiple laminations, and are loaded parallel to the face grain.

A new section, table, and Figure 3 includes end distance, edge distance, and spacing requirements for fasteners in the narrow edge of CLT. Fastener placement provisions are based on CLT cross section dimensions as opposed to individual laminations within the CLT. End distance, edge distance, and spacing requirements for fasteners in the panel face of CLT should be designed in accordance with existing NDS requirements for these fasteners in other wood products.

A new section for lag screws loaded laterally in the narrow edge of CLT was added.

For lag screws installed in the narrow edge of CLT and loaded laterally, in addition to use of Fe for dowel bearing strength,

the connection design value must also be adjusted by the end grain factor, Ceg = 0.67, regardless of whether the fastener is installed in end grain or side grain. The factor is normally applied to end grain applications only, but for CLT it is intended to conservatively account for the mix of end grain and side grain in the narrow edge, and to address difficulties in meeting minimum edge distance requirements if applied to individual laminations of the CLT. For fasteners with D < ¼ inch, Ceg = 0.67 is applicable where the fastener is installed in end grain.

Chapter 13, Split Ring and Shear Plate Connectors, clarifies that provisions for design of these types of connections are not directly applicable to CLT. Possible considerations

Figure 3. Fastener placement figure excerpted from 2015 NDS new Chapter 10 CrossLaminated Timber.

for their use, as part of an engineered design, would need to include requirements for end and edge distance, spacing, and effects of perpendicular crossing laminations.

Chapter 14, Timber Rivets, consistent with design of shear plate and split ring connectors in CLT, clarifies that provisions for design of timber rivet connections are not directly applicable to CLT. Chapter 16, Fire Design of Wood Members, includes a char rate model for CLT based on observations from testing. Accordingly, a

Figure 4. Effective char depth table excerpted from 2015 NDS Chapter 16 Fire Design of Wood Members.

STRUCTURE magazine

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January 2015

new effective char depth equation and table for CLT were added (Figure 4 ).

Structural Composite Lumber In Chapter 8 on Structural Composite Lumber, terminology was added for LSL (laminated strand lumber) and OSL (oriented strand lumber). Structural composite lumber products LSL and OSL are addressed in ASTM D5456 Standard Specification for Evaluation of Structural Composite Lumber Products, but have not previously been defined within the NDS. Added product definitions for LSL and OSL are consistent with those in ASTM D5456.

Chapter 16, Fire Design of Wood Members, was also revised to address structural composite lumber products (PSL, LVL, and LSL).

purchase in electronic format (PDF) only.

Once the NDS Commentary and other support documents to be included in the 2015 Wood Design Package (WDP) are updated, printed copies will be available for purchase. Once the NDS Commentary and other support documents are complete, those who purchased electronic versions of the 2015 NDS and 2015 NDS Supplement will receive those documents in electronic format at no additional charge. Check the AWC website (www.awc.org) for status updates on the 2015 WDP.

Conclusion The 2015 NDS represents the state-of-the-art for design of wood members and connections.

Reference to the 2015 NDS in the 2015 IBC will make it a required design standard in those jurisdictions adopting the latest building code.

However, building officials have the option to accept designs prepared in accordance with newer reference standards even if the latest building code has not been adopted in their jurisdiction. IBC 104.11 for alternate materials and design provides the authority having jurisdiction with that flexibility.▪

Withdrawal Design Values for Lag Screws

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Chapter 12, Dowel-Type Fasteners, clarifies that the withdrawal design value for a lag screw excludes the length of the tapered tip. The addition of “excluding the length of the tapered tip” is consistent with the Table 12.2A table heading which says the length of thread penetration “shall not include the length of the tapered tip.”

NDS Supplement The 2015 NDS Supplement: Design Values for Wood Construction incorporates new design values for southern pine. The American Lumber Standard Committee (ALSC) Board of Review approved changes to design values for all grades and all sizes of visually-graded Southern Pine and Mixed Southern Pine lumber with a recommended effective date of June 1, 2013. Additionally, new and revised grades of machine stressrated lumber and machine evaluated lumber are also included in the 2015 NDS Supplement.

More Details A comprehensive table listing section by section changes to the NDS is available in a web version of this paper available at www.awc.org.

Availability The 2015 NDS with 2015 NDS Supplement is currently available for STRUCTURE magazine

21

January 2015

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Structural rehabilitation renovation and restoration of existing structures

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his series of articles discusses some of the commonly encountered structural issues with renovation projects focusing on historic buildings of this type, and provides guidance on ways to address them.

Part two of this series focuses on wall systems.

Part one, published in the December 2014 issue of STRUCTURE magazine, reviewed common issues with foundations. Part three, to be published in an upcoming issue of STRUCTURE, will focus on historic roof systems.

Unreinforced Masonry Walls The exterior walls of historic houses of worship are typically unreinforced masonry that support the roof and at least some portion of the floor loads. Stone masonry, brick masonry, or a brick or stone back-up wall with stone cladding are the most common exterior wall systems seen in houses of worship in the northeastern U.S., although some smaller structures have wood-framed exterior walls.

Divine Design: Renovating and Preserving Historic Houses of Worship Part 2: Walls

By Nathaniel B. Smith, P.E. and Milan Vatovec, P.E., Ph.D.

Nathaniel B. Smith, P.E., is a Senior Project Manager at Simpson Gumpertz & Heger’s office in New York City. He can be reached at nbsmith@sgh.com.

Dr. Milan Vatovec is a Senior Principal at Simpson Gumpertz & Heger Inc. He can be reached at mvatovec@sgh.com.

Typical Masonry Wall Systems

Although load-bearing, unreinforced masonry (URM) is a very common construction type for exterior walls in buildings built prior to the 1920s, historic houses of worship often feature their own unique variants that can amplify the effects of the expected in-service deterioration, lack of ductility, or weakness in flexure or tension typical for URM elements. The large, open spatial areas within these buildings often create significant distances between levels of lateral support for the walls; unbraced heights of wall can be 30 feet or more. To counteract the slenderness effects of these large un-braced heights, walls are either built very thick (3 to 4 feet or more), or are reinforced with exterior buttresses to provide increased lateral support. The buttresses are typically located between window openings, and are also usually positioned to align with the main roof-framing members (where they bear on top of the wall) to help resist the outward lateral thrust from the roof framing. Buttress can

Spalling of brownstone behind painted cement stucco.

24 January 2015

Spalling of cast stone masonry.

vary in size from relatively small, 3- to 4-foot protrusions, to extremely large, such as the flying buttresses seen in many gothic cathedrals.

The exterior masonry walls also typically feature large window and door openings. The openings can be 20 feet or more in height, and 6 feet or more in width. They will typically feature halfround or gothic arches at their tops and are usually lined with wooden door or window frames. These large openings can significantly affect the ability of exterior walls to act as shear walls to resist inplane loads from wind and seismic effects, and must be carefully considered when undertaking major renovations or alterations.

Deterioration As with any masonry wall, deterioration of the masonry and mortar will occur over time due to exposure to weather and potentially ineffective in-place water-management systems. Repeated wetting and drying of the mortar and masonry, as well as freeze/thaw effects, will cause deterioration of the mortar, spalling of masonry, and formation of cracks or other distress. Exposure-related deterioration or erosion of mortar is typically addressed through periodic repointing of the mortar joints. However, if left unattended, the mortar joints can erode to the point that the support for the masonry units becomes compromised, movement ensues, and additional distress results in the formation of cracks and bulges. If the deterioration is pervasive, significant strengthening or rebuilding of the wall may be the only option. Timely, planned maintenance and repair cycles are key to longevity of these wall systems.

Although stone masonry is typically more resilient than clay-fired masonry, some stones are still susceptible to spalling and other deterioration. Susceptibility of sandstones to spalling depends on how the stone is cut and installed.

Thinner sections of sandstone are often cut along the bedding planes, which is the weakest part of the stone and easiest to cut. The stones are then placed on the building with the bedding plane oriented vertically. Given the relatively porous nature of sandstone, freeze/thaw effects related to the absorbed moisture can often lead to substantial exfoliation of the vertical face (as the

bedding planes delaminate), leading to section loss and more spalling. In some sedimentary stones such as brownstone, clay particles encapsulated within the stone will react with the absorbed water, which then can lead to exfoliation as the now wetted clay creates a weak point within the stone.

In an effort to preserve exterior walls on aging houses of worship, stucco coatings are often applied over the masonry. The stucco is typically cement based, and is often painted.

Older paints are not vapor permeable and will actually create a barrier that traps moisture within the masonry, which accelerates the deterioration processes within the mortar and stonework. Ironically, while the application of stucco and paint was meant to be a preservative treatment, it often amplifies water-management problems. Also, while such situations can “fester” for a while without manifesting themselves, up close examinations and probing can reveal areas where the coating is delaminated from the masonry, and where moisture is trapped within the system.

Loose, delaminated stucco or parging layers are a falling hazard, and should be removed promptly. Periodic inspections and reviews are paramount.

Arched Openings

Preparation of repair area for cast stone with shear pins.

When spalling is present, it can be repaired through application of repair mortars to build out the full cross section of the stone. Mortars can be pigmented to match the existing color of the stone and aggregates can be added to match the texture. All loose material needs to be removed from the existing stone to ensure that the mortar patch achieves a good bond, and deeper repairs (typically greater than 1-inch) may require additional mechanical attachment (shear pins, wire mesh, etc.).

Failure to properly prepare the stone surface prior to applying the patch material will result in premature failure of the patch and is one of the main causes of failure.

Of particular concern when it comes to the condition of masonry and mortar joints are arched openings at doors and windows.

Deterioration of the mortar within masonry arches can cause the masonry units within the arches to shift, or even fall out of the arch.

Loss of masonry and mortar can alter the load path within the arch system, cause the arch to sag and spread, and render the arching action ineffective (arches are meant to resist predominantly compressive forces). This can result in transfer of the building loads into the window or door frames. Therefore, care must be taken when replacing existing frames to make sure that no masonry loads are being carried by the frame prior to removal.

Distress at arches is commonly manifested by cracks running through the peak of the arch.

This can often be remedied by stitching the masonry with mechanical anchors. Helical ties, embedded epoxy bars, or grouted bars can be used to provide mechanical attachment to the arch sections, and cracks can be filled with mortar or epoxy to reestablish the load path through the arch. If substantial movement has occurred (masonry is severely

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January 2015

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Distressed masonry above gothic arch.

displaced), the arch is likely beyond repair and will need to be rebuilt. This will typically require a carefully planned and implemented phasing of shoring, rebuilding, and load transfer (e.g. needle beams to temporarily support the masonry above the arch to allow for rebuilding).

New Openings in Masonry Renovations of historic houses of worship often include proposed new openings in the masonry walls. These openings are typically meant to accommodate new means of egress associated with relocated stairs, or possibly a new elevator. Because the exterior masonry walls are also typically the main lateral-load resisting system (shear walls), creating new openings in these walls needs to be carefully considered. Even without introduction of new openings, masonry walls of this type usually do not meet, nor were they ever designed to meet the lateral load resistance requirements of modern-day building codes.

To complicate matters further, the lateral load path is often not very well defined in these types of structures. In general, lateral loads are typically expected to be transmitted from exterior walls through the floor and roof framing (diaphragms) to the perpendicular walls, which then act as shear walls to resist these forces and transfer them to the foundations. However, any of the elements along this load path may or may not be built with strength and stiffness sufficient for transfer of the design-level forces. Openings within the masonry can only make things worse.

Therefore, when considering new openings in masonry walls, the effect on the overall strength and stiffness of the building needs to be carefully considered. While the building codes typically do not require historic structures, when renovated, to be retrofitted to meet the current load requirements, engineering judgment should be employed to arrive at a solution that at a minimum does not result in weakening of the global lateral-load resisting systems in place. Openings should be sized to minimize the change in the walls’ strength

and stiffness, or additional framing should be added to make up for the loss. For instance, a braced frame or a reinforced concrete or CMU liner (shear) wall can be added within a stair tower to account for new openings.

Consideration of strength and stiffness compatibility and distribution are also important: load paths should be examined, weak links addressed, and alternatives considered.

New openings within masonry walls also need to be able to support masonry and other framing above the opening. This is commonly accomplished by installing steel lintels to span over the opening and support the masonry above. Steel lintels can be relatively easily installed in thin masonry walls (3 to 4 wythe brick walls, and about 12-inch thick stone masonry); however, thicker walls will typically require temporary shoring (e.g. needle beams) to allow local removal of masonry and lintel installation. Once the lintel is installed snug to the masonry above, shoring can be removed, and masonry below the lintels can be removed to create the opening. The need for new openings should be carefully considered, as the effort and expense for creating even a single opening in thick masonry walls can be significant.

Floor Framing Support at Masonry Walls Moisture absorbed by masonry walls can lead to deterioration of the wood framing that bears on the masonry. The orientation of the framing and masonry-pocket configuration typically results in wood end-grain exposure towards the wall exterior. Because of the nature of the wood cell structure, the end-grain of the wood will more readily absorb moisture through capillary action. If the waterproofing system is compromised or overwhelmed, and moisture gets to the wood-member ends, decay (a.k.a. rot) will invariably ensue. The decay process, which turns an ordinarily very ductile wood material into a brittle mass, can significantly compromise the strength of the wood structure and, if allowed to persist, can result in sudden or even catastrophic failures.

This can be especially critical in non-redundant

New lintel at stair opening and new braced frame within stairwell.

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January 2015

Partial-length strengthening of floor joists and new ledger at masonry wall.

systems (often featured in historic house of worship structures), where the majority of floor or roof loading is carried by a relatively small number of members (e.g. roof trusses), and whose failure can affect the integrity of the entire structure. Proactive preventive work (e.g. inspections, maintenance) is therefore critical.

Depending on the extent of the deterioration, reinforcement as well as partial or full replacement of the wood or timber elements may be required to maintain adequate support for the floor framing. Depending on the size and type of the compromised elements, different remedial or strengthening solutions may be available; typically they include some form of supplemental steel or timber framing and temporary shoring. Regardless of the provided remedial design, future exposure, as well as displacement compatibility, connections, and load sharing between the remaining (healthy) members and the new supplemental structure, need to be carefully considered.

For redundant, light-framing systems like wood-joist floors, and if determined that the deterioration mechanism is no longer active (but the extent of decay requires action), simple sistering or full replacement may be an adequate solution. A new ledger can then be attached to the masonry wall to provide additional bearing for the reinforced elements.

Conclusion Unreinforced masonry has been successfully used in building applications throughout the world for centuries. Understanding the characteristics, expected performance, and limitations of these systems allows engineers and architects today to design successful renovation or remedial projects, and to avoid pitfalls that can seriously affect the building’s service life.

It is hoped that the above discussion, which features a number of potential structural issues and possible remedies often seen in practice, helps practitioners in future work on these challenging and exciting buildings.▪

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InSIghtS new trends, new techniques and current industry issues

H

ow much more efficient would structural engineers be if they had access to all of their resources wherever they want? Imagine if resources like construction documents, as-built drawings, project correspondence, calculations, building codes, reference materials, computer analysis programs, product manuals, colleagues, etc. could be carried to every meeting, hauled around to every jobsite and brought home every night. This may not have seemed possible several years ago, but this is exactly what today’s structural engineer can do with the recent advancements in digital technology and tablet style computers.

Apple iPad tablet computer. Courtesy of Apple.

Resources Go Digital In today’s digital world, it is easier and more cost effective than ever to create, manipulate, store and retrieve digital media. Phone calls can be recorded by web-based teleconference services and voice over internet protocol (VoIP) systems.

Digital files can be created and manipulated thanks to advancements in digital scanners and portable document format (PDF) software. Storage of digital files can be hosted on office servers or in the cloud through web-based storage suppliers. Accessing digital media remotely is more efficient thanks to web-based storage suppliers, file transfer protocols (FTP), virtual private networks (VPN) and remote desktop applications.

These advancements have changed the way the construction industry shares information.

Questions and answers can be created and transmitted almost instantly. Coordination between disciplines can occur in real time with teleconferencing and online meeting services. Permit drawings can be digitally signed and posted to web-based servers for submission to the City. Requests for information and shop drawings are transmitted digitally through email, host servers, or online project management systems. Codes, textbooks, testing reports, product manuals, and inspection forms are all available digitally. The digital trend in the construction industry has created

Engineering On-The-Go

By Nick Murphy, P.E.

Nick Murphy, P.E., is an Associate with KPFF Consulting Engineers in Irvine, CA. He can be reached at Nick.Murphy@kpff.com.

Lenovo Yoga Ultrabook computer. Courtesy of Lenovo.

an opportunity for structural engineers to create a virtual workspace with real time access to project files and other resources, provided the engineer has an internet connection and a computer.

Breaking New Ground

Traditionally, laptop computers have been the only mobile computers available to the onthe-go engineer. With the release of iPad and Android tablets in 2010, engineers now have an alternate solution to accessing their resources.

The tablet computer, with its slim profile and lightweight design, allows an engineer access to his desktop computer through VPN and remote desktop software applications. Files stored in the cloud can be accessed through other applications which can then be downloaded and installed on the device. Though not as powerful as a laptop, the tablet can still view and manipulate files seamlessly since it is not functioning as a storage device. While tablets hold some capacity to store files directly on the device, the primary function of the tablet computer is as a portal that allows temporary access to the file before saving it back to the cloud or desktop computer. Its efficiency in downloading and saving files is dependent on the strength of the WIFI or cellular signal that connects it to the Internet.

Structural engineers who have found a tablet computer to be an efficient alternative to a Microsoft Surface tablet computer. Courtesy of Microsoft.

28 January 2015

laptop computer will be the first to say that the device itself is not what has made their life outside the office more efficient.

The efficiency has come from the software that the device utilizes. The applications available to download are as diverse as the engineers who use them. Engineers can take handwritten notes on the tablet during meetings, then convert them to Word documents. They take pictures on a job walk, edit the photos, and insert them directly into field reports. Engineers can also access their construction documents via PDF editors and track field changes as they observe them. Engineers video conference and screen share with their team to resolve issues in real-time. Even drafting and structural analysis applications can allow engineers to answer questions without having to remote access their desktop computer. However, it is not just engineering apps that have made life more efficient. Apps for invoicing, budgeting, expense reporting, traffic, hotel reservations, car rentals, airline reservations, contacts, voice memos, and more are all vital to the engineer on-the-go. The tablet computer has brought all of these resources together in one lightweight package.

Next Generation

• • • • • • • • • • • • •

Access office servers via VPN and remote desktop connections Access cloud storage through Internet connection or applications Access Outlook emails, tasks, contacts and calendars Create and manipulate Word docs, Excel spreadsheets and PowerPoint presentations with the Office for Apple application Create PDF files with applications that print camera images to PDF View and edit PDF files such as construction documents or site photos with PDF viewing applications Take and upload site photos while still onsite with built-in camera Prepare and submit field reports while still onsite Web conference with design team or contractors Screen share with design team or contractors Take handwritten meeting notes that can be transferred to Word documents with note taking applications View AutoCAD files with Autodesk viewer applications Use engineering analysis applications

Field Uses for Ultrabooks and Surface Tablets • • • • • • • • • • • • •

Access office servers via VPN connection Access cloud storage through Internet connection Access Outlook emails, tasks, contacts and calendars Create and manipulate Word docs, Excel spreadsheets and PowerPoint presentations with Windows operating system Create PDF files by printing camera images to PDF View and edit PDF files such as construction documents or site photos with built-in camera Take and upload site photos while still onsite Prepare and submit field reports while still onsite Web conference with design team or contractors Screen share with design team or contractors Take handwritten meeting notes that can be transferred to Word documents with Windows OneNote View AutoCAD and REVIT files using the Autodesk programs Use structural engineering programs installed on the tablet

surface. Both of these new devices can function as a desktop computer by connecting a larger monitor, keyboard (for the Surface), mouse and ethernet cable to its USB and video ports. With the Windows operating system, these devices have their own drives that allow for file storage and program installation directly on the device. This ability to store files and run programs without an Internet connection creates added efficiency for the mobile engineer. Although not as powerful as desktop computers, the Surface and Ultrabooks have a nice balance between portability and computing horsepower.

In the end, with structural engineers, there is never a one-size-fits-all solution. Structural engineers are a unique breed that can be quite particular about their tools. Over the last decade, the structural engineer’s toolbox has grown exponentially with advancements in software development, the advent of the

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January 2015

digital age, and the portable efficiency of the tablet computers. These tools have allowed structural engineers to be more mobile while maintaining the same level of efficiency.▪

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For all their advancements and efficiency, tablet computers are not without their drawbacks. Their lack of storage, processing and graphics rendering power, and a USB port are issues that most engineers can work around, but the tablet’s operating system is something that some engineers just cannot adjust to. Structural Engineers typically function in a PC world. A computer that utilizes Windows as its operating system is likely to be the most efficient, since a structural engineer’s work depends on Windows based programs such as Office, AutoCAD, REVIT, and structural design software coded explicitly for the Windows operating system.

Recognizing the need for a Windows based tablet, Microsoft and other computer developers released their versions of the tablet computer starting in 2012 with the release of the Microsoft Surface. Some companies, such as Lenovo and ASUS, combined the laptop and tablet designs and released devices known as Ultrabooks or Two-inOnes. Whereas the Surface tablet is true to the tablet design with a single touchscreen without an attached keyboard, the Ultrabook looks more like a laptop with an attached keyboard, but it has a large touchscreen that can be rotated into position to create a tablet

Field Uses for iPad and Android Tablets

“G

et in, get out, and stay out” governs the objectives of designing a repair and rehabilitation project on an existing highway facility. Such projects on aging highways need be done as quickly as possible and be long lasting so as to minimize disruptions to a local economy’s infrastructure.

Interstate 280 is a major corridor facilitating traffic in and out of downtown San Francisco. Caltrans maintenance engineers observed the gradual disintegration of hinges on the Southern Freeway Viaduct, a conventionally reinforced box girder bridge built in 1964 and located at the north end of I-280 in the Bay View and Dog Patch Districts of San Francisco. These hinges are located at the overlap of two frames, each consisting of multiple spans supported continually on columns 30 to 50 feet tall. One frame ends with a “seat” while the next frame is supported on the seat, thus forming a joint to allow for primarily thermal movement. Hinges are located at the transition of a negative moment into a positive one. The seat-side superstructure of a span has a negative moment due to the weight of the support-side superstructure adding a reaction force on the nearest bent. The reaction force on the furthest bent is reduced due to support on the seat, which also results in creating the positive moment on the supported side of the hinge.

Theoretically this is depicted by classical statically indeterminate freebody diagrams for a beam with intermediate supports.

Figure 1. Tailgating into barrier forms.

Bridge Hinge Reconstruction Accelerated Bridge Construction for Long Lasting Repairs on Aging Highways

By Ric Maggenti, P.E., Sergio Gomez, P.E. and Roberto Luena, P.E. Rehabilitation work began after constructing temporary supports on both sides of the hinge and closing down this section of viaduct. The existing hinge and 25 to 30 feet of structural box girders of this 53-foot wide bridge were demolished and reconstructed to current Caltrans seismic standards. Removal and replacement included barrier rail and joint seal. The quantity of concrete removed and replaced was approximately 120 cubic yards per hinge. Four hinges and adjacent box girders were reconstructed over 3 holiday weekends. Each weekend consisted of a work window of approximately 100 straight hours, requiring careful planning. Scheduling, logistics, quality control measures, inspections, and selection of materials were paramount to success. Concrete design, mixing, batching and placement technique played no small role.

Project Description As I-280 is vital to a major urban infrastructure, two approaches to construction of the rehabilitation project were considered. The first was staging partial construction of each hinge where at least a portion of the bridge could be available for traffic during construction.

The estimate to do the original 3 hinges earmarked with this kind of staged construction was 140 working days. Working 7 days a week with no weather delays, this would have resulted in inhibiting traffic flow continuously for almost 5 months. When a 4th hinge was slated for replacement, the result would have been over 6 months of traffic inconvenience. Partial construction would also have involved potentially more serious consequences, such as traffic accidents or the hindrance of emergency response vehicles. Additionally, there is a constant risk imposed on construction workers by the proximity STRUCTURE magazine

of moving traffic. The second construction approach considered was to completely close a portion of the viaduct and do an entire hinge during consecutive shifts, adding up to approximately 100 hours. It was determined viable to close the viaduct for these 100 hour periods and, to minimize commuter disruption, the work was scheduled around three separate 3-day holiday weekends (2014 Memorial Day, 4th of July, and Labor Day). For each of the closures, work commenced on the day preceding the weekend and finished in the early morning hours of the day immediately following the weekend. Two hinges were done during the Labor Day weekend. Three hinges are on the northbound structure while one is on the southbound structure.

The 1964 seat and support were 6 inches long across the width of the bridge, while the current seismic standard for hinges in box girder bridges is a minimum of 2 feet long. The 3-mile twin viaduct has hinges approximately every 300 feet. In 1995, the 6-inch seats were retrofitted with bolsters or diaphragms and hinge pipe beams that would provide support if the joint moved more than 6 inches in an earthquake. This was part of the retrofit program following the 1989 Loma Prieta earthquake; the program included enlarging footings and adding steel column casings.

Some retrofitted hinges showed signs of distress over the years. Three northbound hinges and one southbound hinge continued deteriorating until it was deemed they were approaching failure, as spalling concrete had to be caught in nets to prevent injury or property damage below.

Removal To facilitate isolated demolition/removal of the existing structure, temporary supports were required on both sides of the hinge. On

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January 2015

the support side of the hinge, the temporary support was designed to carry the dead load of that span (900 kips). On the adjacent span of the hinge, the temporary support was designed to prevent mid-span deflection and column rotation after the seat was unloaded (800 kips).

The demolition was performed from the deck and had to be done very carefully and strategically so as not to damage the existing structure that was to remain, including exposed longitudinal reinforcement.

Enough existing longitudinal reinforcement needed to remain intact for mechanical staggered splicing to the new construction. The demolition equipment was limited to 1200 ft-lb hydraulic hammers. A CUT Multi Crusher was used to crush and shear through stems (Figure 1). The final removal was hand labor using primarily rivet busters to prevent damage to the portion of the bridge that was to remain. To maintain a clean construction joint, a 1-inch saw cut was made on the entire exterior and interior surface of the superstructure along the construction joint. The entire demolition had a duration of approximately 16 hours.

Replacement After demolition, falsework stringers were erected followed by installation of soffit and stem forms. Some of the existing rebar that was to be spliced did not match contract drawings based on archived

Figure 2. The couplers to mechanically splice the old to the new rebar.

in San Francisco “As-Built” drawings. Anticipating this, extra reinforcement of all sizes and extra mechanical couplers were brought on site along with a mechanical reinforcement bending table (Figure 2). Reinforcement cages for the hinge diaphragms were prefabricated (Figure 3). During the demolition and reconstruction, the structure was monitored/ surveyed continuously at multiple locations for any lateral or vertical movement. Adjustments were made as necessary during demolition and prior to concrete placement.

Concrete Each hinge reconstruction consisted of four pours: stem and soffit on the seat side, stem and soffit on the support side, deck pour seat side and finally deck pour supported side. Barriers and joint seals were the last order of work, notwithstanding clean-up and traffic markings.

Figure 3. A prefabricated rebar cage for the hinge diaphragm.

STRUCTURE magazine

Six weeks prior to Memorial Day, the contractor constructed a mock-up consisting of several stems and soffits and a portion of the hinge seat diaphragm. The mock-up was located on the ground in the concrete company’s yard in Sacramento. Batching and mixing was done by a volumetric mobile concrete truck complying with Caltrans’ Standard Specifications. To simulate the actual procedure, the truck was stationed next to a concrete pump and discharged concrete into the pump truck’s hopper. Since each placement sequence required more than the capacity of a truck, the concrete materials were replenished during placement as was the plan for the job site.

Aggregates were continually loaded into the truck’s bins with skip loaders while the truck’s cement hopper was replenished using prepackaged 1 ton super-bags lifted by crane. A water truck was used to keep water in the water tanks. A truck could hold about 10 cubic yards so the mock-up was to be more than one cycle, and thus the 16 cubic yard mock-up was deemed appropriate. Also, the largest element was a hinge diaphragm. To ensure compliance with Caltrans’ Mass Concrete requirement that a concrete element does not exceed 160 degrees F, the hinge diaphragm mock-up temperature was monitored.

Peak temperature was well under 160 degrees F, thus no additional precautions were required. The truck and 2 back-up trucks were certified during the mock-up.

At the bridge site, aggregate stock piles were located on the deck spread out over several bents. Note concrete technology evolved to using the absolute volume method for batching concrete to address the bulking characteristic of aggregate with its changing volume with changing moisture content. Absolute volume practice uses weight to batch ingredients to address effects of bulking due to moisture.

The stock piles were covered with plastic sheeting to maintain a near constant moisture content, particularly the sand stock piles, mitigating bulking characteristics and allowing for more accurate batching by volume. Cement super-bags were stored under the bridge. Continuous metering displaying volume per time of the ingredients and automatic

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January 2015

Date

Location (Hinge Span)

5/24/14 5/25/14 5/26/14 5/26/14 7/4/14 7/5/14 7/6/14 7/6/14 8/30/14 8/30/14 8/31/14 8/31/14 8/31/14 9/1/14 9/1/14 9/1/14

ES-83, Stem and Soffit, Seat Side ES-83, Stem and Soffit, Supported Side ES-83, Deck, Seat Side ES-83, Deck, Supported Side A-80, Stem and Soffit, Seat Side A-80, Stem and Soffit, Supported Side A-80, Deck, Seat Side A-80, Deck, Supported Side A-83, Stem and Soffit, Seat Side SE-59, Stem and Soffit, Seat Side A-83, Stem and Soffit, Supported Side SE-59, Stem and Soffit, Supported Side A-83, Deck, Seat Side SE-59, Deck, Seat Side A-83, Deck, Supported Side SE-59, Deck, Supported Side

Unit Weight (pcf) 150.2 151.14

151.26 151.68 152.03 151.83 151.63 151.83 151.03 150.93

4-hr break (psi) 3598 3718 3385 3560 3333 3430 3743 3960 3283

5-hr break (psi) 3780

3683 3793 4033 3928

3888 3650 3260 3985 3830 3680

151.93

Total count 11 Average 151.41 Std. Dev. 0.55 Coef. of Var. 0.4%

4.5-hr break (psi)

3738

4025 3930 9 3556 222 6.3%

7 3697 225 6.1%

7 3903 112 2.9%

Figure 4. Unit weights and early strength.

Figure 6. A view of a removed hinge and box from below.

Figure 5. Compressive strength vs. time.

dispatching tickets were required. Unit weights on samples taken during placement were used as a check on proportioning. Figure 4 shows how consistent the unit weight was throughout the entire project. The lowest unit weight correlated with the initial higher slump during the very first placement before water was slightly adjusted to achieve the desired 5- to 7-inch slump for placement.

The structural concrete design complied with 2010 Caltrans’ Standard Specifications for Rapid Strength Concrete. This material’s specification is based on the award winning I-10 Pomona Freeway project specifications constructed in 1999. Approximately 2 lane-miles of the 8 lane mile project on a heavily traveled portion of the I-10 was replaced during a 55 hour weekend window, with the remaining 6 lane miles completed during nighttime closures over a period of several months. The specification allows for any fast-setting cement meeting ASTM c219 for hydraulic cement. If other than a Portland cement is used, then some additional requirements are listed to ensure long-term durability. The contractor chose a calcium-sulfoaluminate cement as the fast-setting hydraulic cement ingredient, which happened to be manufactured by the same company providing the cement on the Pomona project.

The contractor was able to control the mix with admixture adjustment as the temperature varied and as the placement needs varied.

There was no dead time waiting for strengths. The working time was engineered to be about an hour, so by the time the top of a stem was finished, the soffits achieved final set. The contractor’s crews were openly impressed has to how soon forms could be stripped so as to move on to the next operation. The last concrete placement was the barrier rail placement. Because it could be tailgated and a shorter STRUCTURE magazine

working time could be easily accommodated by the nature of the element, that mix was engineered to produce 1 hour compressive strength of 2,000 psi on cylinders heated to approximately match the actual in-place temperature of the barrier concrete.

Cylinder break data are also shown in Figure 4. The cylinder breaks had coefficients of variation falling within the standard of concrete control range category of “very good” as classified by the American Concrete Institute per ACI 214 R-02. This coefficient of variation demonstrated consistent batching and mixing, and consistent properties of cement, aggregate and admixtures, thus achieving the high degree of quality control confirmed by quality assurance results. Figure 5 shows the strength gain with time up to 3 months.

Conclusion All the preliminary planning and diligence of the contractor, the mockup, calibration of the mixer trucks, unit weight sampling taken during placement confirming proper mix proportions, the required care taken on the aggregate stock piles to ensure uniformity, standard QA sampling and testing, and the attention to detail during design and construction, resulted in achieving the objectives of this rehabilitation project.▪

32

Ric Maggenti, P.E. (ric.maggenti@dot.ca.gov), Materials & Research/Bridge Engineer, Caltrans; Sergio Gomez, P.E. (Sergio_ gomez@dot.ca.gov), Bridge Construction Engineer Representative, Caltrans; Roberto Luena, P.E. (Roberto_luena@dot.ca.gov), Area Bridge Construction Manager, Caltrans.

Project Team Owner: Caltrans Construction Contractor: Golden State Bridge Inc. Concrete Supplier: Precision Concrete Materials LLC Fast Setting Cement Supplier: CTS Manufacturing Corp.

January 2015

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AdAptive Reuse investigAtion of Roof fRAming Historic Bush Terminal Complex, Brooklyn, New York

By D. Matthew Stuart, P.E., S.E., F.ASCE, F.SEI, SECB, MgtEng

I

Figure 1.

ndustry City in Brooklyn, New York retained Pennoni Associates, Inc. (Pennoni) to complete an evaluation of the existing roof structures at Buildings 2, 3, 5, 9, 10, 19, 20 and 26 of the historic Bush Terminal Complex (Figure 1). The primary purpose of this effort was to determine the load-carrying capacity for new “green” roofing systems, solar panel arrays and other adaptive reuse proposals.

Due to the lack of original structural drawings, it was necessary to field-determine the internal reinforcement of the concrete system at a typical bay in each building. This involved creating small inspection openings to expose the reinforcement at areas of the framing where removing insignificant amounts of concrete material would not compromise structural integrity (Figure 2). This approach, used in conjunction with a Profometer (or Pachometer), enabled the

determination of the existing reinforcing in the immediate area surrounding the exploratory openings.

Pullman Shared Systems Technology, Inc. (Pullman), as a subcontractor to Pennoni, performed the exploratory demolition; WJE, as a sub-consultant to Pennoni, conducted the Profometer readings.

The approximate concrete compressive strength was obtained by using a Schmidt (or Impact) Hammer in the same vicinity.

Figure 2.

Figure 3.

STRUCTURE magazine

History and Description of the Buildings The buildings in the Industry City complex were constructed between 1904 and 1911, and were originally referred to as the Bush Terminal Company facility. A search of available historical records revealed

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that the architect, engineer and contractor, for most if not all of the buildings, were William Higginson, E.P. Goodrich and Turner Construction Company, respectively. Additional history of the site can be found at http://industrycity.com/history/ All of the buildings associated with the investigation were constructed as conventionally reinforced, cast-in-place concrete structures.

Building 26 was constructed as a two-way flat slab with drop panels and column capitals, which were all supported by round concrete columns (Figure 3). All of the other buildings were framed as oneway slabs, joists and beams, which were supported by either round or square concrete columns (Figures 4 and 5 ). The buildings varied in height from six to twelve stories, not including basements.

In general, the existing roof structures were in good condition, with painted soffits, and supported suspended loads such as lighting/ electrical, sprinklers and piping, as well as rooftop loads such as steel piping, electrical power lines and small mechanical equipment. The roofs also included skylight openings, most of which that had been removed and enclosed with supplemental framing (Figure 6 ).

The roofing systems at all of the buildings, except for Building 2 (which had been recently reroofed), were in very poor condition, which was confirmed via roofing cores that were obtained by Pullman. The primary purpose of the roofing cores was to determine the weight of the existing roofing systems, which varied between 1.0 and 6.0 psf.

Figure 4.

Analysis and Material Testing The assumed strength of the reinforcing bars was based on information provided in an out-of-print book entitled Reinforced Concrete in Factory Construction, published in 1907. This publication included an entire chapter dedicated to the design and construction of Building 2 and indicated that the floor live load was 200 psf. Additional research of other historical publications, including the 1911 edition of The American Architect magazine, indicated that the six-story buildings at the complex were designed for a floor live load of 150 to 400 psf and a roof live load of 75 psf.

Because of the limited access available to the top flexural reinforcing in the slab, joists and beams, the analysis of these members was based on the positive moment capacity of the sections determined from the exposed bottom flexural reinforcing at the exploratory openings located at the soffit and midspan of the selected typical members.

The assumed dead loads included the self-weight of the framing, the weight of the roofing system and an additional 3.0 psf to account for miscellaneous suspended mechanical loads. The minimum roof snow load, based on the governing building code, was 20 psf.

The results of the initial analysis and report indicated that, in some cases, the reserve load-carrying capacity of the existing roofs under investigation was considerably less than the 70 psf load capacity documented in the available historical references. As a result of this initial conclusion, which was based on a tensile strength, ft, of the reinforcing bars of 16 ksi as documented in the same historical references, and in conjunction with the proposed use of the roofs as public assembly space with a live load of 100 psf, Pennoni recommended material testing of the reinforcing bars.

Samples of the bottom flexural reinforcing of the same roof joists that had previously been subjected to exploratory demolition were obtained at the end of the members immediately adjacent to the supporting beams (Figure 7 ). An additional similar sample from a beam was also obtained from Building 20 at the end of the member immediately adjacent to the supporting column. The bottom flexural reinforcing sample from the flat slab in Building 26 was removed immediately adjacent to a drop panel. A reinforcing steel sample could not be obtained in Building 9 STRUCTURE magazine

Figure 5.

Figure 6.

Figure 7.

35

January 2015

Table 2.

Table 1.

Description

Yield Strength Sample Size (fy) ksi

Building

Maximum Allowable Reserve Load Capacity

2

248 psf

5

188 psf

Building 2 Joist

44.8

7/8-inch diameter

Building 5 Joist

49.2

0.905-inch square twisted

9

145 psf *

Building 10 Joist

56.0

0.915-inch square twisted

10

310 psf

Building 19 Joist

44.5

Not Recorded

19

277 psf

Building 20 Joist

53.5

Not Recorded

20

104 psf

26

180 psf

Building 20 Beam

54.5

0.915-inch square twisted

3

143 psf

Building 26 Slab

39.6

5/8-inch diameter

Building 3 Joist

54.5

0.875-inch square twisted

*The value listed for Building 9 is based on an assumed yield strength (fy ) of 40 ksi. If material testing is not conducted, it should be reduced to 87 PSF, which is based on a historical maximum available yield strength of 30 ksi confirmed by CRSI.

because of limited access and the lack of bottom reinforcement in the available redundant areas of the joist investigation.

The samples were exposed using similar exploratory demolition methods with 6- to 8-inch-long samples of the reinforcing steel removed and sent to a laboratory for testing. The damaged area of the remaining reinforcing steel was not repaired, because the samples were obtained from an area of the member in which there was no positive moment, therefore the presence of the bottom flexural reinforcement was redundant. Table 1 summarizes the test results.

The results of the material tests indicated that the actual yield strength (fy) of the reinforcing bars varied from 39.6 ksi to 56.0 ksi. This magnitude of strength is considerably greater than the previously known highest grade of vintage reinforcing steel documented by the Concrete Reinforcing Steel Instituting (CRSI) that was in use at the time, which was Grade 30 (fy = 30 ksi; ft = 16 ksi). CRSI confirmed that the use of reinforcing steel as high as Grade 40 to 56 in the first decade of the 1900s at these buildings is an anomaly from previous historical records for the same era.

Reanalyzing the roof framing, based on the actual yield strength per the material testing, resulted in a considerable increase in the Maximum Allowable Reserve Load Capacity noted in Table 2. These values already account for the self-weight of the structure, the miscellaneous mechanical superimposed dead load, the dead load of the existing roofing system and snow load. With the exception of Building 26, and as indicated in Table 2 for Building 20, the results are based on the joist capacities, which were always less than that provided by the beams.

In general, it appeared that most of the roofs, except for Buildings 3 and 20, were designed and constructed for approximately the same floor live load of 200 psf as documented in the historical records. It is also not unusual to be able to justify a higher live load capacity than that intended by the original design by using current ultimate strength methods, rather than the working stress methods used at the beginning and middle of the 20th Century. Therefore, it is not surprising that, in some cases, the load carrying capacities documented by the ultimate strength analysis resulted in capacities greater than 200 psf.

The primary reason why the capacity at Building 20 is significantly less than that at the other buildings is because it has approximately one-half of the beam reinforcing provided in the other one-way beam roof structures. It is not clear why this was the case. Using the Profometer, an investigation of other similar beams in Building 20 in the same column line as the subject typical beam indicated that STRUCTURE magazine

similar reinforcing – only two 0.915-inch square twisted bars – was provided in all of them. Thus, it is very likely that the reduced load carrying capacity of the Building 20 roof structure is widespread and typical for the entire building.

Conclusions It is important to note that the results of this investigation were based on a typical, repetitive bay of roof framing in each building. Any atypical bays or framing members that are different from that analyzed may not have a comparable reserve load-carrying capacity as that documented for the typical bay. In addition, the original or supplemental framing associated with existing skylights or subsequently enclosed skylight openings were not included in this investigation, so the capacity of these areas should be investigated before any change in their usage.

It was Pennoni’s understanding that the roofs at a number of buildings were intended to be used as public assembly spaces, such as outdoor theatres. Chapter 16 of the NYC Building Code requires a minimum live load of 100 psf for Assembly Areas and Theatres with movable seats, and does not make a distinction about the level of the building at which this occupancy occurs.

Except for Building 9 – in the absence of material testing as required to justify a yield strength greater than 30 ksi – it appeared that all of the buildings associated with the investigation had adequate reserve load carrying capacity for this function.

Additional adaptive reuse concepts such as that proposed at Building 19, which will include the construction of a new raised roof over a portion of the building footprint and rooftop terrace facilities, should be evaluated on a case-by-case basis. More conventional methods of adaptive reuse, such as solar arrays (maximum 10 psf ) and “green” roofing systems (maximum 25 psf ), can be installed safely at areas that correspond to the typical bays investigated.

This project served as a good example of how a responsible property management company completes the due diligence necessary for a proposed adaptive reuse of an existing facility.▪

36

D. Matthew Stuart, P.E., S.E., F.ASCE, F.SEI, SECB, MgtEng (MStuart@Pennoni.com), is the Structural Division Manager at Pennoni Associates Inc. in Philadelphia, Pennsylvania.

January 2015

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14-10479

Foundations

U.S. ConStrUCtion Spending Up Foundations Companies Offering New Products, Services

By Larry Kahaner

C

onstruction spending in the United States rose more than expected in October – in both public and private sectors – logging a 1.1 percent increase, the largest gain since May according to the Department of Commerce.

This data suggests some momentum for the fourth quarter of 2014.

Overall, U.S. construction reached an annual rate of $970.99 billion.

Construction looks strong on a global scale too, according to KPMG’s 2013 Global Construction Survey which shows “an industry in better shape than four years ago with rising backlogs and largely healthy margins. The recovery in the global economy is driving infrastructure, power and energy projects, while cheaper gas prices are leading to manufacturing growth.”

Amid this backdrop of positive data, many foundations companies are seeing increased work.

“Although we are staying busy right now in most major market sectors, we are seeing a big increase in the use of ground improvement methods in the construction of multi-use [residential and commercial] structures, in particular in urban areas where old fill soils are a significant concern,” says Lyle Simonton, Director of Business Development for Subsurface Constructors, Inc. (www.subsurfaceconstructors.com) in St. Louis, Missouri. “Projects are using stone columns/aggregate piers in fill soils, providing a significant increase in bearing pressure and therefore a higher ‘trust’ factor with building on marginal sites.”

Since the start of its Ground Improvement Division in 2005, the 108-year old company continues to grow its ability to perform work in new areas of the U.S. each year, Simonton says. “By continuing to invest in new technology and with our in-house innovation in improving our equipment and techniques, we have put ourselves in a competitive position for projects across much of the U.S.” Simonton notes that he’s hearing from SEs who want to work with Subsurface Constructors to help develop their projects. “They are trying to bring value to their clients by optimizing the foundation STRUCTURE magazine

“Although we are staying busy right now in most major market sectors, we are seeing a big increase in the use of ground improvement methods in the construction of multi-use [residential and commercial] structures, in particular in urban areas where old fill soils are a significant concern.” type for the existing soil conditions and we’re able to help them develop the most economical solution. Subsurface Constructors is one of the only specialty contractors in the U.S. who provides both deep foundations and ground improvement services, so we can provide a true assessment on what foundation type is feasible and economical.”

One recent project is “The Streets of St. Charles” site in St. Charles, Missouri, a multi-use project that consists of an apartment structure, retail, office space, and a movie theater. This site had significant grade changes and very soft soils in most areas. Subsurface Constructors worked closely with the general contractor to develop earth retention solutions to support the large cuts on the site, and used multiple ground improvement types to accommodate new construction of footings in soft soils and some restricted access areas. Subsurface was involved in the project planning process for close to two years prior to construction, and therefore could help the design team make important decisions regarding foundation type, earth retention, and construction sequence, Simonton says. continued on page 41

39

January 2015

Geopier is Ground improvement.™ Work with engineers worldwide to solve your ground improvement challenges.

the Geopier Gp3® system: controllinG settlement we help you fix bad Ground.

For more information call 800-371-7470, e-mail info@geopier.com or visit geopier.com.

Plans for the 150,000 square foot Avalon Irvine apartment complex in Irvine, CA featured a common “wrap” style structure, with 4-story apartments surrounding a 4.5-story parking garage. The site was underlain by 20 to 25 feet of soft to medium stiff lean clay with groundwater encountered at depths of 8 to 10 feet. The clay was underlain by stiff clay and dense sand to a depth of 50 feet.

Reconciling the settlement tolerances between the apartments and the parking structure presented a unique design challenge. The GP3® system was an ideal solution, meeting the specified settlement tolerance for 1” total foundation settlement and ½ inch differential between the parking structure and the apartments. By reducing total settlements and accelerating time rate of settlement for all structures, GP3 eliminated the need for a 6-9 month surcharge.

©2014 Geopier Foundation Company, Inc. The Geopier® technology and brand names are protected under U.S. patents and trademarks listed at www.geopier.com/patents and other trademark applications and patents pending. Other foreign patents, patent applications, trademark registrations, and trademark applications also exist.

Foundations G

eopier Foundation Company (www.geopier.com) in Davidson, North Carolina is also experiencing a good year. President Kord Wissmann says: “2014 is a record year for Geopier, and we are looking forward to continued success in 2015. While the overall markets remain strong, we believe that it’s our wide variety of continuously evolving ground improvement solutions that afford great value to our clients.”

The company, a subsidiary of Tensar Corporation, says that it developed the first Rammed Aggregate (RAP) system in 1989. Today, Geopier solutions provides an efficient and cost effective Intermediate Foundations solution for the support of settlement sensitive structures, company officials say. They note that its systems have become effective for massive over-excavation and replacement of deep foundations including driven piles, drilled shafts or augered cast-in-place piles.

Adds Wissman: “Our GeoConcrete Columns are being used for heavy loads on very soft soil sites, and our Geopier X1 system is providing opportunities to efficiently reinforce deep compressible cohesive soil previously reserved for deep foundations.”

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STRUCTURE magazine

41

January 2015

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ile Dynamics, Inc. (www.pile.com) of Cleveland, Ohio redesigned several of its instruments in 2014. “The Pile Integrity Tester model FV and the Thermal Integrity Profiler got larger and more visible screens,” says Gina Beim, Senior Consulting Engineer/ Marketing Director. “But the Pile Driving Analyzer (PDA) system got a complete top-tobottom redesign of both hardware and software.”

Says Beim: “The new Pile Driving Analyzer system is the PDA-8G model. Like previous PDAs, the PDA-8G uses data obtained by sensors attached to a pile to calculate capacity and more than 230 other quantities once a driving hammer or other drop weight hits the pile.”

“The thickness of the PDA-8G is less than half of the model it replaces and it feels light and ergonomic, like a tablet. Engineers who are familiar with the PDA will appreciate that the data acquisition channels of the PDA-8G are now all universal, allowing the use of various combinations of accelerometers and strain transducers. This is attractive for tests of large drilled/cast-in-place piles,” Beim says. “Data may be collected at 120 blows per minute – almost fifty percent faster than before – making it easier to test piles driven by hydraulic hammers with high blow rates. The PDA software now responds to gesture controls like swiping and pinch-to-zoom, making for a very intuitive interface. It also includes more extensive data input help and output customization. The PDA-8G is SiteLink-ready [SiteLink technology transmits PDA test data via the Internet to an engineer located

Foundations

elsewhere who follows the test in real time], giving the engineer the option of conducting the test remotely. A totally revamped version of the CAPWAP software that analyses the data collected with the PDA-8G was also released.”

Beim concludes: “Pile Dynamics manufactures an instrument that monitors the installation of augered cast-in-place piles, the PIR [Pile Installation Recorder]. Certain U.S. industry guidance documents recommend the use of such instruments – the generic name is Automated Monitoring Equipment – whenever this type of pile is installed. PDI both sells and rents the PIR, and this year the number of rentals increased significantly. PDI sells this mostly to the U.S. market, where augered piles are typically favored by the private sector.

They are a relatively inexpensive deep foundation solution.”

A

t Hayward Baker, Inc., (www.haywardbaker.com) whose North American Headquarters are in Hanover, Maryland, Director Jim Hussin says that soil mixing is continuing to grow. “That’s the process where soils are mechanically mixed with binders, usually cement, to end up with a stronger material. It’s being used more and more, especially in soft sites where you have either soft clays or weak materials that are difficult to treat using other technologies.”

Hussin adds: “In the south Florida market we’re using it more frequently to create what we call ‘bathtubs,’ where the [developer] wants to build high-rise condominiums but they also want to put three or four-story parking garages below them which is difficult because it’s right on the beach. A 30-foot deep excavation adjacent to the Atlantic Ocean is extremely hard to do. Before they do an

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STRUCTURE magazine

42

January 2015

excavation, we’ll spin tools down and mix from 30 to 40 feet.

This creates a floor down below the planned excavation. We then create walls on the side. We’re building a ‘bathtub’ which they can dig out and have a dry excavation. Then they’re able to construct lower floors and go on up with their high-rise. That’s something in the last year or so that’s really taken off.”

As for the market in general, Hussin sees improvement. “We’re seeing after a couple years of the [the recession and aftermath] that there’s been a steady climb and we’re back to where we were pre-recession days. We’re seeing a nice, steady growth in the construction industry. It’s not extremely fast but nice and steady, so I think it’s probably a good, healthy growth,” he says.

Hussin would like SEs to know that Hayward Baker has the ability to construct projects designed by others but also performs design-build projects. “The diversity that Hayward Baker offers, along with our engineering ability, allows us to assist engineers with evaluating and resolving sub-surface issues with the right, best fit for whatever the project is.

A

t CTS Cement Mfg. Corp. (www.ctscement.com) in Cyprus, California, Marketing Director Janet Ong Zimmerman says the company manufactures Rapid Set fast-setting hydraulic cement and Type K shrinkage compensating cement. “Rapid Set exceeds 3000 psi in one hour, which means you can make structural repairs and rehabilitation and return the concrete to full use in one hour,” Zimmerman says. She wants SEs to know about Rapid Set Flooring Products

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STRUCTURE magazine

43

January 2015

Foundations

that “offer a complete way to repair, resurface and renew interior and exterior floors.” She adds: “Products include TRU SelfLeveling for polished overlays and toppings, Skim Coat for patching and skim coating, and repair mortars.” In addition, the company is touting Rapid Set Corrosion Inhibitor which provides triple-protection against corrosion. “It increases corrosion resistance when used in areas susceptible to corrosion and chloride. It repels water, thereby preventing an unsightly appearance to concrete. It reduces chloride permeability, thereby increasing the life expectancy of metals, steel and rebar,” Zimmerman says. (See ad on page 41.)

H

ollie Furimsky at Ram Jack Systems Distribution in Ada, Oklahoma, (www.ramjack.com) notes that its helical design software Ram Jack Foundation Solutions allows an engineer to custom design a helical pile per their project specifications, share projects with other registered users, and save a PDF output for submittals. “Ram Jack’s engineering department, staffed with structural and geotechnical engineers, assist engineers with designs, drawings, specifications, and technical questions. If the engineer of record is not familiar with helical or hydraulically driven steel pilings, our engineers can provide the pile

design, calculations, drawings, and specifications for the engineer’s review,” she says. “Ram Jack Manufacturing ensures the quality and assurance of our products through our ISO-9001 certification. We also hold a Fabricator’s License per the City of Los Angeles Building Department. Ram Jack continues to maintain our ESR report (ESR1854) and have updated it to include compliance to the 2012 IBC and the 2010 Florida Building Code. We have also updated our L.A. Research Report for compliance with the 2014 L.A. Building Code.”

Furimsky adds: “Ram Jack Foundation Solutions software and engineering consulting services are provided free of charge to design engineers. Our product reports and ISO certifications demonstrate Ram Jack’s commitment to quality control and assurance of our products, as well compliance to the building codes.”

She says that they have seen an average of 20 percent growth in product sales across the board. Helical piles have had the largest growth.

“We strive to be a leader in our industry. Our commitment to the engineering community has always been to provide the most trusted steel piling system on the market. Our offerings and services are geared to helping engineers specify our products with confidence,” Furimsky concludes.▪

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STRUCTURE magazine

44

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news and information from anchor companies

Decon® USA Inc.

Phone: 866-332-6687 Email: frank@deconusa.com Web: www.deconusa.com Product: Studrails® Description: The North American standard for punching shear enhancement at slab-column connections. Studrails are produced to the specifications of ASTM A1044, ACI 318-08, and ICC ES 2494. Decon Studrails are increasingly used to reinforce against bursting stresses in banded posttension anchor zones.

Product: Anchor Channels Description: Decon USA is the exclusive representative of Jordahl in North America. Hot rolled Anchor Channels are embedded in concrete and used to securely transfer high loads. Their main application is for flexible connections of glazing panels to high-rise buildings. Anchor Channels with welded-on rebar or corner pieces are available.

Gripple Inc.

Phone: 630-406-0600 Email: grippleinc@gripple.com Web: www.gripple.com Product: Concrete and Metal Deck Insert Solutions Description: The original cable hanger solution for all types of suspended services. Spider: cast-in-place concrete insert solution, designed to prevent accidental movement before or during the concrete pour. Metal Deck Insert: pre-insert solution for metal decks. Both are available as complete kits that include a Gripple cable hanger.

Hohmann & Barnard, Inc.

Phone: 631-234-0600 Email: weanchor@h-b.com Web: www.h-b.com Product: 2-Seal™ Thermal Wing Nut Anchor Description: An innovative Single Screw Veneer Tie for steel stud and concrete construction that features a dual-diameter barrel with factory-installed EPDM washers to seal both the insulation and the air/vapor barrier. The wing section is encapsulated with ul-94 plastic to decrease thermal transfer through rigid insulation and is highly flame-resistant.

IES, Inc.

Phone: 800-707-0816 Email: info@iesweb.com Web: www.iesweb.com Product: VAConnect 2.0 Description: Steel base plates and shear tabs too, are what we will design for you. Those anchor ‘calcs’ (Appendix D) are also dealt with easily.

Kelken Construction Systems, Inc.

Phone: 732-416-6730 Email: ken@kelken.com Web: www.kelken.com Product: Keligrout Structural Anchor Adhesive Description: Keligrout is a superior high strength polyester resin anchoring material with guaranteed pullout values exceeding ACI-349-85. Keligrout can be used in sub-freezing temperatures or in and under water. Every lot of material is guaranteed and certified.

Powers Fasteners

HALFEN USA

Phone: 816-896-4266 Email: pschmidt@halfenusa.com Web: www.halfenusa.com Product: Anchor Channels Description: Halfen is a global leader in design and manufacturing of anchor systems for concrete. Hot rolled anchor channels for edge or top of slab transfer high loads while also providing field adjustability.

Custom anchors are available for special corners and thin slab conditions.

Hardy Frame

ANCHOR UPDATES

Phone: 800-524-3244 Email: engineering@powers.com Web: www.powers.com Product: Type 316 Stainless Steel Wedge-Bolt Description: Powers Fasteners has expanded the popular Wedge-Bolt anchor line to offer a version in Type 316 stainless steel for concrete and masonry.

These new 300 series stainless steel screw anchors are for applications requiring additional corrosion resistance such as railings and exterior attachments.

S-FRAME Software Inc.

Phone: 800-754-3030 Email: dlopp@mii.com Web: www.hardyframe.com Product: Hardy Frame Shear Walls Description: Hardy Frame now offers pre-engineered anchorage solutions that drastically reduce the large pad footings that have become associated with prefabricated Shear Wall Panels. Standard details are available to include with plan submittals.

Phone: 203-421-4800 Email: info@s-frame.com Web: www.s-frame.com Product: S-CONCRETE Description: S-CONCRETE displays instantaneous results as you optimize and design reinforced concrete walls, beams and columns. Automate your workflow by checking thousands of concrete section at once. With comprehensive ACI1 318-11 design code support, S-CONCRETE produces detailed reports that include clause references, intermediate results and diagrams.

STRUCTURE magazine

45

January 2015

Product: S-FOUNDATION Description: Quickly design, analyze and detail your structure’s foundations with S-FOUNDATION, a complete foundation management solution. Run as a stand-alone application, or utilize powerful 2-way integration links for a detailed soil-structure interaction study. S-FOUNDATION automatically manages the meshed foundation model and includes powerful Revit and DXF data links.

Simpson Strong-Tie

Phone: 800-999-5099 Email: web@strongtie.com Web: www.strongtie.com Product: Simpson Strong-Tie® Blue Banger Hanger® Description: Blue Banger Hanger has received the first International Building Code (IBC) report issued for a specialty cast-in-place insert. The code report (ICC-ES ESR-3707) is the first one for this type of anchor under ICC-ES AC 446. It covers all sizes of Blue Banger Hanger wood form inserts.

Product: AT-XP® Fast-Curing Anchoring Adhesive for Cracked and Uncracked Concrete Description: AT-XP is a fast-curing anchoring adhesive formulated for high-strength anchorage of threaded rod and rebar into concrete under a wide range of conditions. AT-XP adhesive dispenses easily in cold or warm environments with little to no odor.

It has demonstrated superior performance in reducedtemperature testing (14°F (-10°C)).

StrucSoft Solutions

Phone: 514-731-0008 Email: marketing@strucsoftsolutions.com Web: www.strucsoftsolutions.com Product: Metal Wood Framer Description: A template-based and rule-driven extension to Autodesk® Revit® for framing. It empowers users to automate the modeling, clash detection & manufacturing of light gauge steel and wood framing including shop drawings, cut lists, BOM, optional CNC output & more.

Tekla

Phone: 770-426-5105 Email: kristine.plemmons@tekla.com Web: www.tekla.com Product: Tedds Description: Tedds Anchor Bolt and Column Base plate modules analyze cast-in-place and post-installed anchors in concrete. It covers ACI Appendix D along with multiple generations of the ACI 318 codes. Its ease and speed of use have made it a vital addition to many engineering firms around the world.

All Resource Guide forms for the 2015 Editorial Calendar are now available on the website, www.STRUCTUREmag.org.

Historic structures significant structures of the past

I

ron bridges in Great Britain date from 1779 when the cast iron Coalbrookdale Bridge was built across the Severn River.

It was followed in 1796 with a bridge by Thomas Telford at Buildwas just upstream from Coalbrookdale. Telford also built several aqueducts of cast iron, as well as two other roadway bridges at Craigellachie in 1814 and Betws-yCoed in 1815. He even proposed a cast iron bridge with a 600-foot span in 1799 to replace the London Bridge across the Thames River.

In the United States, men like Timothy Palmer, Theodore Burr and Lewis Wernwag built major wood bridges, with Burr and Wernwag using some wrought iron in their bridges. It wasn’t until Capt. Richard Delafield built an 80-foot span arch bridge, across Dunlap’s Creek near Brownsville, Pennsylvania on the National Road in 1839, that iron was used as a major bridge material. It consisted of five flanged, elliptical tubular arches with the sections bolted together. In 1836 Delafield wrote, “In some one of my communications of last fall I intimated that I had matured in my mind the plan of the Cast Iron Bridge to be constructed over Dunlap’s Creek–differing in its principles of construction from any of which I could find a notice by either English or French Engineers...” James Finley also used iron loops in his early suspension bridges. It wasn’t until Earl Trumbull built a small bridge at Frankfort, New York that cast and wrought iron were used in a truss like bridge. Trumbull patented his bridge on July 10, 1841. It consisted of 7 cast iron sections with a top and bottom chord

The Whipple Bowstring Truss

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

Dr. Griggs specializes in the restoration of historic bridges, having restored many 19 th Century cast and wrought iron bridges. He was formerly Director of Historic Bridge Programs for Clough, Harbour & Associates LLP in Albany, NY, and is now an independent Consulting Engineer.

Dr. Griggs can be reached at fgriggs@nycap.rr.com.

Whipple Patent Application Drawing.

46 January 2015

and diagonals. The verticals were half cylinders used to bolt the sections together. In addition, wrought iron rods dropped down from the top ends of the truss to the lower chord in a parabolic curve. Trumbull had no idea how to size his cast and wrought iron elements. It was, therefore, a combination of truss and suspension bridge. It fell down shortly after its erection. Even though rebuilt, it never received any fame other than that associated with being the first iron bridge over the canal.

It was into this environment that Squire Whipple (STRUCTURE, September 2005) entered the field of bridge engineering. Since graduating from Union College in 1830, he had worked on the B&O Railroad, the Northern Railroad between Ogdensburg and Lake Champlain and the New York and Erie Railroad before moving to the enlargement of the Erie Canal under Holmes Hutchinson. The canal was being enlarged from a 40-foot width at the surface to a 70-foot width and a depth increase from 4 feet to 7 feet. This required a large number of longer span bridges to cross the 363-mile long canal.

Whipple wrote of his entry into bridge building as follows, “(A)t the time when I entered the field as a candidate for the honors and profits of skillful bridge construction, nearly all the principles and feasible general combinations had long been in use. So there was little for me to do but to select the best combinations, best materials, and the proper dimensions and proportions of the several parts and members to secure adequate strength without waste of material or unnecessary expense of labor and workmanship.”

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After some thought he came up with his bowstring iron truss arch on August 22, 1840. His design and intent were to: “...construct an iron truss to be used in connection with a wooden floor system, the truss to have sufficient stability to stand of itself, without any dependence upon the wood, so that the latter could be renewed from time to time as might be required, without disturbance or danger to the iron work.

And, as an evidence of the complete success of the effort, it may be mentioned that a single model truss six feet long (scale 1/12 size) sustained without transverse support or assistance of any kind, a load of 900 lbs. (representing 129,600 lbs. upon a full truss) without the least indication of yielding, or want of complete stability.”

He submitted his design to the Patent Office, and was awarded Patent No. 2,064 on April 24, 1841.

He was not claiming that he was the inventor of the bowstring truss. He was claiming the use of cast-iron segments in combination with wrought iron diagonal ties or braces to sustain the form of the arch against the effects of unequal loadings. He also claimed the use of thrust ties, the string in the bow and string bridge, to sustain the thrust and spreading of the arch. His last claim was use of a diverging top chord, either in wood or iron, to give the arch or truss lateral stability, hence the independent iron arch truss bridge.

Whipple knew the exact role each piece of his truss would play, and how to size the member so that it could play that role. His use of cast iron in compression and wrought iron in tension was based on economic considerations, as wrought iron was only available in small bars or round stock and was very expensive.

Therefore, he used the cheaper cast iron for most of his bridge. In practice, Squire ended up using the options to his main proposal rather than the original plan. For instance, he quickly went to single verticals through the joint rather than double verticals offset from the segmental joints. On the “string”, he went to wrought iron loops rather than spliced flat bar stock. His proposed wood truss, while interesting, is beyond the scope of this paper.

Why he threw in the option of using buttresses to support the lateral thrust of the arch rather than the “string” is not known. He would still have needed some element to tie the suspended verticals and diagonals together.

No evidence exists that he ever built one of his bowstrings with buttresses. He actually calculated the loads in his truss members but

Vischer’s Ferry Bridge across the Enlarged Erie Canal. Bridge was originally across the Erie Canal at Sprakers and later across Cayadutta Creek in Fonda, New York.

did not publish his method until 1846-47 in his book, A Work on Bridge Building: Consisting of Two Essays, the One Elementary and General, the Other Giving Original Plans, and Practical Details for Iron and Wooden Bridges. For this work, A. P. Boller called Whipple “the retiring and modest mathematical instrument maker, who, without precedent or example, evolved the scientific basis of bridge building in America.”

He now had a patent and design that he knew, from a life cycle cost standpoint, was superior to any wooden bridge in use. He still had to convince the Canal Commissioners that iron bridges were a good investment and would, over time, more than justify their higher initial cost. What he needed was a customer! He built and tested a six-foot long model of his bridge, but this hadn’t convinced the Commissioners that a large-scale bridge, using cast and wrought iron, would act in the same way. What he did would seem rash to many people, but given his options it was probably the only way he could have sold the Commissioners on his idea. He went to his brother-in-law, Oliver Shipman who ran an iron works in Springfield Center, New York, and built a full-size, seventy-two foot span, bowstring truss using $1,000 he had saved. It was a single freestanding bridge on a vacant lot next to the drug store in downtown Utica, New York, inviting people to see and test it. The following item appeared in the Utica Observer dated March 9, 1841: “I have been shown within a few days past, a structure erected in our city. It is the framework of a bridge made of cast and wrought iron. The inventor is Mr. Whipple, civil engineer of this city. The erection is merely a single frame, of a size adapted to that of the

new bridges, over the enlarged Erie Canal, for the purpose of illustrating the plan of Mr. Whipple, to cover all spans, from a single canal crossing to the largest railway aqueducts. It stands opposite to Bushnell’s shop on Seneca Street, immediately below the corner of Lafayette Street, where any one may have an opportunity of visiting it and examining its merits.”

The commissioners could not avoid seeing the arch, as it was only a block away from the canal near the weigh house at Bleeker Basin.

This, his first “experimental” bridge, was later built over the canal at Newville (near Rome) in 1845, his second bridge over the canal.

Whipple wrote of this effort, “Look at that experiment, standing idle and useless for some four years, during a part of the time the work of enlargement was suspended, in a public place, exposed to the idle gaze of passers by, most of whom doubtlessly, congratulated themselves on not having been born with a propensity for visionary schemes and experiments; while some probably looked at the thing as not entirely a mere monument of visionary folly, but as a work possessing merits which ought to produce profitable returns to the projector.”

Shortly after, when the wooden bridge across the canal at First Street in Utica fell, Whipple contracted to build his first bridge over the canal for the sum of $1,000 in the spring of 1841.

He now had something to show the doubters, as his bridge was not only durable but, with its arches, was almost graceful and did point the way to materials of the future. Interestingly enough, this bridge served until September 16, 1922 when the canal was closed and the Barge Canal opened using the Mohawk River.

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The Stop Work Law of 1842 slowed the enlargement of the Canal, so few other Whipple Bridges were built until 1848 and then only a few until the 1850s. In 1851, the Commissioners adopted the Whipple Independent Iron Arch for use on the canal.

In 1854, they decided to place the entire remainder of the enlargement out to bid at one time, called the Big Letting, indicating to all bidders that they would be responsible for paying Whipple’s patent fees. Whipple wrote a letter to the Commissioners on September 24, 1854 giving his patent fee as $.50/ft for a bridge with sidewalks and $.40/ft. for a bridge without sidewalks. It wasn’t until April 17, 1858 that the Canal Board officially accepted Whipple’s proposal, after others had built 30 of his bridges to his patent. In a letter to the Canal Board, he listed the 30 bridges and told them they owed him $2,540.80 in patent fees.

The Board agreed they owed him that amount in 1859, but the legislature did not pass any authorization for payment. On March 29, 1862, the Legislature finally agreed to allow the Canal Board to settle with Whipple, which they did for a sum of $1,236.09. In the meantime, Whipple and others had built hundreds of Whipple’s bowstring truss across the Canal.

Whipple wrote a little ditty as follows, “These little bridges I invented, Ratty gets the pay.

Thus not for self, ye birds your nests do build, Thus not for self, ye sheep soft fleeces yield, Thus not for self, ye bees your honey stow, Thus not for self, ye oxen drag the plow.”

He renewed his patent in 1855, extending its life to 1862. The bridges were not only built across the Erie Canal but across rivers using multiple spans. When the Erie Canal was filled in, many of the bridges were relocated to other sites and used for many years. The author has restored Whipple Bowstrings at Vischer’s Ferry, Boonville, and Union College, all in New York and is currently part of a team rehabilitating the two span Whipple Bridge, the Shaw Bridge, at Claverack, New York. Other Whipple’s are across the Normanskill in Albany, New York and in Newark, Ohio on the Campus of Ohio University (restored by Jim Riddell). A bridge to Whipple’s plan is located in Tokyo, Japan called the Old Tojo or Hachiman Bridge.

Whipple’s bowstring was the first successful cast and wrought iron bridge built in the United States, and the first bridge with each element sized to carry its load under varying placement of the load on the bridge. It set the stage for the Bollman and Fink Trusses that were to follow. For this, and other reasons, Whipple has been called “The Father of the Iron Truss Bridge.”▪

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award winners and outstanding projects

Spotlight

The Distinctive ‘Floating’ Roof of Jasper Place Library

By Derek Ratzlaff, P.Eng Fast + Epp was an Outstanding Award Winner for the Jasper Place Library project in the 2014 NCSEA Annual Excellence in Structural Engineering awards program (Category – New Buildings under $10M).

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he City of Edmonton recognizes the value of building high-quality civic facilities for its citizens; hence the architectural response for their newest library that called for a striking free-form clear span facility with maximum daylight penetration.

Fast + Epp collaborated with Hughes Condon Marler Architects and Dub Architects to construct Jasper Place Library, a 15,000 square foot replacement of an existing facility.

Predominantly cast-in-place concrete on piles, the primary feature is the expressive curved plate concrete roof that spans the entire library space, punctuated with skylights.

The structural design team faced numerous challenges in the execution of the design, not the least of which was assuring the Client that the proposed structural concept was both safe and buildable. In addition, it was desired that the library would act as the civic heart of a neighbourhood, and that its architecture would be reflective of that concept. The goal was to create a flexible, open space that could adapt to the needs of the library as it evolves in the future.

The unusual structural design consists of a concrete roof slab that cascades into concrete walls at two sides and is supported by light steel columns at the front and back. The roof relies on the deep wave form to clear span the space and generous allowance was made for skylight openings. This design concept is not reliant on additional shear walls or bracing for lateral stability, with the result being a structure that appears to float under maximum daylight penetration.

To maximize the effect of a ‘floating’ roof structure, engineers eliminated bracing or shear walls in the normal-to-wave axis direction. Typical frame action relying on a 300-mm-thick (12-inch) slab/column structure to transfer lateral loads over an effective 30-meter (98-foot) building width would result in unacceptable stresses and deformations. The ingenuity of the structural solution lies in the system availing itself of the inherent longitudinal stiffness of each wave. The ‘spring stiffness’ of each wave reduces the effective frame width to the distance between the axis

of the wall columns and adjacent waves, thereby providing the necessary strength and stiffness when subjected to wind and seismic loading.

Fast + Epp embarked on a series of analyses to determine the wave shapes and attendant skylight openings in the roof slab that would result in optimal structural strength and architectural effect.

Cast-in-place concrete as well as wood and steel frame solutions were all considered. A concrete option with post-tensioned ‘troughs’ became the preferred solution as a result of the anticipated economy, ease of incorporating organically-shaped openings and its clean architectural expression. The final design incorporates varying wave heights – both normal and parallel to the axes of the waves.

Location and size criteria for skylights and acoustic panel depressions were established, enabling generous slab perforations of up to 10 square meters (108 square feet).

A key challenge lay in how to deal with the large cantilevered overhang condition near the front entry of the building – both from a structural strength and thermal bridging point of view. Schoeck Isokorb thermal breaks from Germany were incorporated to minimize thermal bridging in extreme cold climate conditions. A combination of cantilever behaviour as well as two-way slab action in the wedge-shaped corner was relied upon to achieve the necessary structural strength.

Accommodating the large punching shear forces in column support regions that arose from evenly-spaced columns that did not always align with stiff peak and trough points was another challenge. This was successfully dealt with by reinforcing the high-stress regions with stud rails.

Constructability challenges were also identified early in the design process, and the City solicited an expert opinion to advise whether the design was both structurally safe and achievable in the Alberta construction climate. Fast + Epp showed the Client and peer reviewer precedent cases of complex concrete structural forms while explaining the inherent logic of the design – including the

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Courtesy of Stephan Pasche.

use of post-tensioning in the trough regions to control deformations. However, it was not until a satisfactory construction procedure was proposed, accompanied by detailed costing, that these fears were adequately allayed and the go-ahead for final design and construction was given.

The project achieved economy of design by incorporating flat surfaces between the peaks and valleys. It was also proposed to pour the flatter slopes, including the valleys, without top forms prior to pouring the steeper sloped roof and peak portions. This simplified the formwork and enabled pouring of the sloped roof surfaces without excessive wet concrete pressures in the trough regions.

With the digitalization of reading material becoming more popular, the City of Edmonton wanted to create a space that would house tangible reading material, and more importantly serve as a social space for the community. The final design features an open space devoid of columns and allows for the opportunity of maximum social potential in the coming years.

Targeting LEED Silver, the striking architectural form and ample daylight of Jasper Place Library has resulted in a happy and sustainable space for users. Favorable feedback from both the Client and the public has testified to the value of creative design.▪ Derek Ratzlaff, P.Eng, contributes a strong knowledge of wood frame construction to his work as a structural engineer. He was appointed an Associate in 2013, assuming a primary role as mentor for Fast + Epp’s young engineers and fostering professional development within the firm. Derek has acted as Project Engineer for numerous challenging projects, with a particular focus on those utilizing hybrid wood-steel and wood-concrete combinations on a large scale.

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NCSEA News

News form the National Council of Structural Engineers Associations

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President’s Message

Moving Up Requires Effort Barry Arnold, P.E., S.E., SECB, NCSEA Board President Great leaders have six characteristics in common: an insatiable curiosity – they are always looking to enhance their current level of knowledge and performance; a willingness to learn – they want to complement their current understanding with new ideas and material; a willingness to seek expert advice – they seek mentors and coaches with proven credentials to guide them toward higher efficiency, accuracy, and monetary rewards; they associate with people who have similar problems and diverse views – they want to be found among peers that want to be successful and have found ways to overcome their problems; they know that in an ever-changing world success can be fleeting – they know they must continually spend the time and effort to consistently be on top; and they know that time is precious – they want to invest every minute in opportunities that will produce the greatest rate of return.

All the great leaders embrace these six concepts with passion.

That is true of the great leaders in politics, sports, science, and business. They know that true success is not inherited but earned through personal sacrifice, continual education, and determination. They know that to be truly successful they must invest continuously in improving themselves and their company. There is no ‘Easy Button’ for true and lasting success.

There never has been and never will be.

Much fantasy literature has been written about the self-made man – the person who comes from nowhere and with nothing and somehow they miraculously and against all odds achieve great success. It’s the stuff of legends and dreams. The problem is that it didn’t happen that way – ever. Those that achieve great success follow the rules of success – all six concepts.

The myth of the self-made man is a primary cause of many business failures. People think starting and running a business will be easy and jump in with wild expectations and dreams of riches and respect, without understanding the amount of

work and knowledge involved. Success takes personal effort and dedication, combined with a life-long commitment to pursue knowledge.

Operating and building a business can, to paraphrase Charles Dickens, “be the best of times, it can be the worst of times, it can be the age of wisdom, it can be the age of foolishness…”

The outcome of any business venture is irrevocably linked to the effort put into learning and managing the business from sources that respect your time and maximize your ROI by providing valuable, relevant, and current information you can use. There is no greater challenge than running a successful business, and there is no greater reward than having run it well.

NCSEA wants to assist you on the road to success by providing an opportunity to attend the Winter Leadership Forum.

Whether you’re just starting out and wondering where to begin; or if you dealing with growth, client, or employee problems; or if you’re getting to the age where you want to retire and want to sell your business, NCSEA wants to assist you in finding the best answers to the questions you have.

The WLF provides ample opportunity to mingle with your peers, to share experiences and ideas that will strengthen your place in the market. It’s the place to be to compare notes and openly and safely share successes and failures and receive advice.

It’s the place where great leaders come to hone their business acumen and plan for the future.

For the past two years, the WLF has been the place where those that were serious about their careers and businesses met to discuss current trends. It’s been the place for those with insatiable curiosity, for those with a willingness to learn and share experiences, and for those open to seeking expert advice and the advice of peers. Those that attend want to be and stay successful. They know that they must expend time and effort to consistently be on top, and they know that time is precious and they want to invest in opportunities that will produce the greatest rate of return. The WLF is the place where great leaders gather.

At the WLF you won’t find just a single answer to a problem, you will find lots of answers, a variety of diverse viewpoints from leaders who know the ropes. You will not find any fluff at the WLF – just practical solutions to the problems you face. The WLF isn’t a vacation. It is an opportunity for you to invest in yourself and in your company.

NCSEA is dedicated to helping seasoned and novice business owners obtain and share the knowledge and skill to navigate the complicated business environment. The 2015 Winter Leadership Forum will be held in Coral Gables, Florida on January 29-30. Register online at: www.ncsea.com/meetings/winterleadershipforum/.

“I enjoyed the interactive format and the lively discussions from diverse perspectives. Well worth my time.”

“A perfect mix of networking and business learning. The Winter Leadership Forum will be on my calendar every year.”

Ed DePaola, P.E., SECB President & CEO Severud Associates Consulting Engineers

Chris Hofheins Principal BHB Consulting Engineers

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Thursday (continued)

Friday (continued)

AEC Business Development: The Decade Ahead – Scott Butcher, Brad Thurman What works, what doesn’t and how do clients want to be sold? The SMPS Foundation interviewed more than 100 buyers and sellers of A/E/C services to answer these questions and will share their findings.

Ideas to Get Your Firm Hired and Retain Relationships – Part II

Increasing Your Engineering Firm’s Value to Your Client This panel will focus on ways to increase billable hours, increase and provide more comprehensive services, and improve specialties.

Panelists: Scott Butcher Robb Dibble Brad Thurman

Case Study: To Purchase or To Pass

Greg Kingsley Mike Tylk

– John Tawresey This interactive case study will focus on whether or not to acquire another firm.

Attendees will function as the Board of Directors making this decision.

Friday

Organic Growth vs. Growth by Acquisition This debate and panel discussion will focus on avenues for firm growth, their pros and cons, and understanding which approach, if any, is right for your firm.

Moderator: Jonathan Hernandez, Partner, GMS Debate Moderator: Robb Dibble Participants: Organic Growth: Mark Aden, DCI Engineers Growth by Acquisition: Bjorn Morisbak, Stantec

Moderator: Scott Butcher, VP, JDB Engineering Panelists: Robb Dibble, Principal, Dibble Engineers Carrie Johnson, Principal, Wallace Eng. Greg Kingsley, President/CEO, KL&A Mike Tylk, Principal (retired), TGRWA

January 13, 2 015 Behavior, Design & Special Installation of Adhesive Anchors January 20, 2 015 Design Examples using the ACI Anchorage Provisions February 10, 2 015 Practical Solutions to Frequently Asked Welding Questions

Discuss and develop new strategies, and learn what other principals are doing and thinking.

Platinum Sponsor:

The Winter Leadership Forum will take place at the scenic Hyatt Regency Coral Gables in Florida. The hotel is located just steps away from beautiful beaches, lush fairways and dozens of shops. The Hyatt Regency also hosts a pool and an award winning fine-dining restaurant, Two Sisters.

Register at www ncsea.com February 26, 2015 The Structural Engineer’s Role in Building Community Resilience More detailed information on the webinars and a registration link can be found at www.ncsea.com. These courses will award 1.5 hours of continuing education. Approved for CE credit in all 50 States through the NCSEA Diamond Review Program. Time: 10:00 AM Pacific, 11:00 AM Mountain, 12:00 PM Central, 1:00 PM Eastern.

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Plan offers an individual access to all NCSEA live webinars over a one-year period. This option is only open to NCSEA members, i.e., members of NCSEA MO’s, Affiliate, Associate and Sustaining Members. Enrollment form and details are available at www.ncsea.com.

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Take your seat at the table.

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Ideas to Get Your Firm Hired and Retain Relationships – Part I This panel presentation and discussion will focus on pre-positioning, business development, and go/no-go decisions for project pursuits.

Moderator: Carrie Johnson

– Terry Vanderaa, Steve Van Drunen Providence Bank Chairman Terry Vanderaa and Bank President Steve Van Drunen will discuss how engineering firms and banks can develop relationships that benefit both parties, how banks analyze firms, and how banks view growth opportunities.

News from the National Council of Structural Engineers Associations

Moderator: Robb Dibble, Principal, Dibble Engineers Panelists: Greg Kingsley, President/CEO, KL&A Brad Thurman, Principal & Chief Marketing Officer, Wallace Engineers Mike Tylk, Principal (retired), TGRWA

Technical abilities alone are not sufficient for long-term success. The panel will discuss ideas on how you can train your employees for successful interaction with your clients.

Banking Relationships

NCSEA News

Thursday

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The Newsletter of the Structural Engineering Institute of ASCE

Structural Columns

Call for Abstract and Session Proposals Now Open Connect disciplines, soils, and structures. Collaborate and provide better solutions. Build structures and relationships.

Be part of the technical program for this unique event featuring dynamic sessions and presentations on topics addressing both Geotechnical and Structural Engineering issues. Final papers are optional and will not be peer reviewed. Consider submitting either session proposals or single abstracts related to the topics and subtopics of interest to both professions.

The 2016 joint Congress will feature a total of 15 concurrent tracks: there will be tracks based on traditional GI and SEI topics, and tracks on joint topics. In addition, we will be offering interactive poster presentations within these tracks.

All proposals must be submitted by April 7, 2015 (no extensions).

Visit the joint conference website at www.Geo-Structures.org for more information and to submit your abstract.

Second ATC-SEI Conference

ASCE Week

Improving the Seismic Performance of Existing Buildings and Other Structures December 10-12, 2015 Hyatt Regency San Francisco Call for abstracts and session proposals now open – submit your proposal before January 22, 2015 Organized by the Applied Technology Council (ATC) and the Structural Engineering Institute (SEI) of the American Society of Civil Engineers (ASCE), this conference will be dedicated to improving the seismic performance of existing buildings and other structures.

All proposals must be submitted by January 22, 2015 (no extensions). See the conference website at www.atc-sei.org/ for more information and to submit your abstract.

March 16 – 20, 2015 Orlando, Florida Build up the professional development hours you need for license renewal while enjoying an escape from winter in Orlando. ASCE Week is coming March 16-20, 2015. You can even earn 4 PDHs in a private tour of the engineering of Walt Disney World. ASCE Week brings together in one location our most popular face-to-face seminars from leading experts. Enjoy discounted seminar fees and save up to $800 when you sign up now for two seminars. Register today at www.asce.org/continuing-education/asce-week/.

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

Registration Now Open for Structures Congress 2015 New ideas. New practices. New science. New resources. New colleagues.

April 23 – 25, 2015 Portland, Oregon Early bird registration rates available until March 4, 2015. Highlights include: • Over 110 outstanding technical sessions will be offered on all areas of structural engineering • Earn up to 15 PDHs • Networking events on all days of the congress, including breakfasts, plenary lunches, exhibit hall reception, and reception at the World Forestry Center • CASE Spring Management Convocation • All committee meetings on Wednesday – will not conflict with other congress activities • Exhibit hall featuring the latest products and services in structural engineering • Bike and Streetcar tours of Portland structures and infrastructure available Visit the congress website at www.structurescongress.org for more information and to register.

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The ASCE/SEI Committee of Composite Construction and the ACI 335 Committee of Composite and Hybrid Structures have joined together to form one joint committee. The name of the new joint committee is SEI/ACI Composite Construction Committee. The first chair of this joint committee will be Prof.

Amit Varma from Purdue University. A new committee chair will be selected to start in fall 2015. The next meeting of this joint committee is scheduled on April 22, 2015, immediately before the ASCE Structures Congress 2015. The committee is sponsoring two sessions at the Structures Congress: Art and

Science of Composite Construction and Advances in Composite Beams, Floors, and Diaphragms. Additionally, the joint committee is working on two documents: Design Guidelines for Connections between RC Columns and Steel Beams and State-ofthe-art Report on Connections between CFT Columns and Steel Beams. If you would like to join the committee please visit the SEI website at www.asce.org/structural-engineering/ sei-tad-committee-application/. For more information about the committee or to contribute to the reports mentioned above, please email Amit Varma at ahvarma@purdue.edu.

Local Activities St. Louis Chapter

The SEI Sacramento Bridge Committee and the Japan Society of Civil Engineering met on October 9, 2014 to exchange technical knowledge on bridge maintenance condition and repair methods. Civil engineers in the United States and Japan learned from each other as they shared common interests in methods of access to bridge structures, identifying and documenting conditions, creating solutions and discussing best practices.

San Francisco Chapter SEI is pleased to announce that the ASCE San Francisco Section Board unanimously approved the establishment of an SEI Local Chapter. During its inaugural year, the San Francisco SEI Local Chapter will focus on establishing a chapter board that will outline a vision with goals for the chapter, and the development of by-laws. Additionally, the chapter will host and/or participate in a handful of technical activities. In order to successfully carry out the above, the chapter needs members. Interested members in the San Francisco Bay Area can join and become a part of this exciting endeavor. Please contact the Chapter Chair, Edward Thometz at ethometz@stanfordalumni.org.

West Virginia University Graduate Student Chapter The SEI Graduate Student Chapter at West Virginia University (SEIGSC) participated in the 2014 EngineerFEST, a yearly festival organized by the Freshman Engineering Program. This event is a great way to get freshmen involved with campus activities and organizations. Over 1000 students participate each year. The SEI event table consisted of Fiber Reinforced Polymer (FRP) composite samples, Nondestructive Evaluation (NDE) demonstration, informational posters, and details of a current FRP bridge rehabilitation research project.

STRUCTURE magazine

East Central Florida SEI Chapter and Central Florida SEI Graduate Student Chapter Fourteen middle and high school robotic teams participated in a hands on CAD modeling and design training at the University of Central Florida. Special thanks to East Central Branch of the FL Section of ASCE, East Central SEI Chapter of Florida ASCE Section, PTC, Renaissance Robotics, and University of Central Florida SEI Graduate Student Chapter for joining forces and hosting the first annual “Tesla University”. The students learned the basics of modeling robots, visualization perspectives, and 3D rotation. In short order, they were able to model a car and make the wheels rotate. The new skills that the students learned during this training will enable them to better compete in the upcoming season of competitions.

Get Involved in SEI Local Activities Join your local SEI Chapter, Graduate Student Chapter, or Structural Technical Groups (STG) to connect with colleagues, take advantage of local opportunities for lifelong learning, and advance structural engineering in your area. If there is not an SEI Chapter or STG in your area, talk with your ASCE Section/Branch leaders about the simple steps to form an SEI Chapter. Visit the SEI website at www.asce.org/SEI and look for LAD Committees.

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The Newsletter of the Structural Engineering Institute of ASCE

Sacramento Chapter

On October 3, 2014, SEI St. Louis provided the third annual SEI Day at the Masonry Institute of St. Louis. Over 60 members attended the full day of seminars. The seminars included discussion of the new Stan Musial Veterans Memorial Bridge, Design of High Performance Industrial Floors, Collapse of Agricultural Grain Bins, Steel Erection Procedure of the Illinois Bridge over the Illinois River, Parking Structure Repair, Evaluation and Repairs of Bridge Gusset Plates, Common Errors in Seismic Design and How to Avoid Them, and Developments in Fastening Technology. Speakers were from HNTB, ESI, WHKS, Wiss, Janney, Elstner Associates, Heausler Structural Engineers, Euclid and Hilti. The event was well received and thanks are extended to the speakers.

Structural Columns

ACI & SEI Create New Joint Committee on Composite Construction

CASE in Point

The Newsletter of the Council of American Structural Engineers

CASE 2014 BEStSEllErS Now Available!!

These publications, along with other CASE documents, are available for purchase at www.booksforengineers.com.

Guideline Documents 962:

Risk Management Toolkits

National Practice Guidelines for the Structural Engineer of Record (SER)

1-1: Create a Culture for Managing Risks and Preventing Claims

962-A: National Practice Guidelines for the Preparation of Structural Engineering Reports for Buildings 962-D: A Guideline Addressing Coordination and Completeness of Structural Construction Documents 962-G: Guidelines for Performing Project Specific Peer Reviews on Structural Projects

1-2: Developing a Culture of Quality 5-1: A Guide to the Practice of Structural Engineering 9-1: A Guideline Addressing Coordination and Completeness of Structural Construction Documents

SAVE THE DATE CASE Winter Planning Meeting and Roundtable

Contract Documents #1:

An Agreement for the Provision of Limited Professional Services

#2:

An Agreement between Client and Structural Engineer of Record (SER) for Professional Services

#3:

An Agreement between Structural Engineer of Record and Consulting Design Professional for Services

#11: An Agreement between Structural Engineer of Record (SER) and Contractor for Transfer of CAD Files on Electronic Media

February 5 – 6, 2015 Doubletree by Hilton New Orleans The CASE Winter Meeting features concurrent committee meetings, a networking reception, and a structural engineering roundtable, worth two professional development hours.

Interested in attending? Please contact Heather Talbert, htalbert@acec.org, for more information.

WANTED

Engineers to Lead, Direct, and Get Involved with CASE Committees!

If you’re looking for ways to expand and strengthen your business skillset, look no further than serving on one (or more!) CASE Committees. Join us to sharpen your leadership skills – promote your talent and expertise – to help guide CASE programs, services, and publications.

We have a committee ready for your service: • Risk Management Toolkit Committee: Develops and maintains documents such as business practices manuals and policies for engineers under CASE’s Ten Foundations for Risk Management.

Follow ACEC Coalitions on Twitter – @ACECCoalitions.

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Expectations and Requirements To apply, you should: • be a current member of the Council of American Structural Engineers (CASE) • be able to attend the groups’ two face-to-face meetings per year: August, February (hotel, travel reimbursable) • be available to engage with the working group via email and conference call • have some specific experience and/or expertise to contribute to the group Please submit the following information to htalbert@acec.org • Letter of interest • Brief bio (no more than 2 paragraphs) Thank you for your interest in contributing to your professional association!

January 2015

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.

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 in pursuing their dreams to become professional engineers is to offer incentives in educational support.

In addition, the CASE scholarship offers an excellent opportunity for your firm to recommend eligible candidates for our scholarship. If your firm already has a scholarship program, remember that potential candidates can also apply for the CASE Scholarship or any other ACEC scholarship currently available.

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 tax deduction and you don’t have to be an ACEC member to donate! Contact Heather Talbert at htalbert@acec.org to donate.

CASE Risk Management Convocation in Portland, OR The following CASE Convocation sessions are scheduled to take place on Friday, April 24: 7:00 AM – 8:15 AM CASE Breakfast: The Future of Structural Engineering Sue Yoakum, Donovan Hatem 8:30 AM – 10:00 AM Addressing Hidden Risks in Today’s Design Contracts Speakers – Rob Hughes, Ames & Gough; Brian Stewart, Collins, Collins, Muir & Stewart 10:30 AM – 12 Noon How to Succeed Without Risking It All! Moderator – John Dal Pino, Degenkolb Engineers 1:30 PM – 3:00 PM Lessons Learned From Structural Cases in Litigation Speaker – Jeffrey Coleman, The Coleman Law Firm 3:30 PM – 5:00 PM SE Practice for Quality and Profitability – Panel Discussion

Strengthen your Competitive Edge Increase your Decision-Making Skills Does your company have data but lack insight? Is the rapid pace of change a challenge to timely decision-making? Is valuable time wasted searching for just one more piece of data?

As a leader of a small firm, you face increasingly complex decisions–decisions that are filled with ambiguity, uncertainty and risk. To remain competitive, you can’t wait for complete data and certainty. To save time and money, you must decide and decide now. It’s easy. Successful leaders know the secret.

They gather as much information as feasible and they pay attention to intuition – gut feel. Powerful decisions come from balancing cognition and intuition in a skilled internal calculus. New research in neuroscience reveals the proven processes your brain uses to perform that calculus. Now you can harness that power for the management of your firm and development of future leaders.

STRUCTURE magazine

Through these sessions, discover practical skills that put neuroscience to work for you and your business so that you can avoid the pitfalls of over-thinking; sidestep analysis paralysis; learn techniques to simplify complex decisions; and develop future leaders who are both smart and insightful.

Increase your decision-making skills now at ACEC’s Small Firm Council’s (SFC) annual Winter Meeting, February 20-21 in Nashville. Speaker, Coach and Author, Shelley Row, P.E., of Shelley Row Associates LLC will ignite an interactive exploration of complex decision-making based on her personal interviews with over 70 leaders. The data confirms that the most effective leaders make decisions by gathering information while trusting their intuition. That remarkable combination is what Shelley calls infotuition™. Don’t over-think it! Join the discussion today.

Infotuition™…You’ve got it. Are you using it? To register, visit www.acec.org/coalitions.

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January 2015

CASE is a part of the American Council of Engineering Companies

The CASE Risk Management Convocation will be held in conjunction with the Structures Congress at the Doubletree

by Hilton Downtown Hotel and Oregon Convention Center in Portland, OR, April 23-25, 2015. For more information and updates go to www.seinstitute.org.

CASE in Point

Donate to the CASE Scholarship Fund!

Structural Forum

opinions on topics of current importance to structural engineers

The Case for Three Significant Figures

By Phillip C. Pierce, P.E., F.ASCE

H

ow many of you notice the number of significant figures presented within your firm’s calculations? Prior to the advent of pocket calculators, engineers prepared their calculations by hand, supplemented with a slide rule.

Their tool of choice was the traditional 10-inch slide rule limited to three figures. The few who owned a 20-inch slide rule could interpolate results to four figures. Of course, they were able to carry hand calculations out to as many figures as desired, but there was rarely a need to do so. Senior engineers would even counsel and coach young or inexperienced staff to limit their results to fewer digits with appropriate round-off. The rounded values were an acknowledgement of the many levels of unknowns or assumptions made in each string of calculations. This training was just one of the ways mentors challenged young staff to develop a sense of judgment about the results.

Accuracy was important, but what mattered even more was having an understanding of the results.

Then the calculators came.

The rapid proliferation of affordable small calculators brought forth a tendency to copy down the results from a display without much reflection. Older staff could still employ “rapid mental arithmetic” to provide an approximate answer with a properly placed decimal point as fast as, or even faster than, one could with one of these “new-fangled” machines. However, most engineers simply pulled out a calculator and recorded the output, which almost always showed at least eight digits. With the development of affordable programmable computers, engineers began relying on them to perform tedious and repetitive calculations. More refined analyses came afterwards and invariably provided an ever-increasing number of digits, implying even more precision and more accuracy.

To the detriment of the profession, the retirement of seasoned practitioners is making way for new generations consisting largely of slaves to software and hardware. Gone are the days when production staff prepared Fortran language programs to perform complex calculations, such that the programmer actually had to know what the program did and assumed. Now business economics often demands the purchase or lease of available software to use without proper training.

Sometimes the software does not even include detailed explanations of its built-in assumptions. It is no wonder that errors of use are commonly made. Veterans must be the only ones who remember the real definition of “GIGO” – garbage in, garbage out! As a consequence, staff is finding it more difficult to recognize erroneous, impractical or misleading results.

True, some engineers continue to do routine – and sometimes not so routine – calculations with spreadsheets. They can be wonderfully beneficial tools, but often these engineers make little effort to limit the number of digits shown in the results, let alone ensure that values are labeled with their units.

And it is not just calculations! Values are sometimes shown on construction drawings that are not only totally impractical, but also inappropriate. What good are concrete dimensions to the nearest

1/16th inch; jacking pressures to the nearest psi; or stations, elevations and offsets to the thousandths of a foot? It is pretty obvious why construction workers laugh at engineers when they show up in the field.

How about estimates of construction cost? Does anyone really think that an engineer can estimate the unit price of an item for a construction bid to the nearest penny and honestly believe it? The same can be said about quantity estimates. This is why round-off is imperative.

Precision has almost become a sport. Staff members argue about the “accuracy” of their work and mark up each other’s values, which are neither accurate nor precise, for correction during the checking process. They do all of this while wasting the precious commodity of time. But what use is extra time when it will only be spent driving the profession to distraction?

Compounding this absent-minded tendency to believe and copy down whatever the computer output says is the ever-increasing complexity of codes and standards. As an aged bridge engineer, it boggles this author’s mind that we have allowed our national design specifications to evolve to the point that it now takes a wheelbarrow to transport a hard copy. The average length of the roughly 600,000 bridges in the United States is about 150 feet. Is such a large number of detailed provisions really necessary to design such a bridge? To one without much experience with other types of structures, the International Building Code seems just as bad in this regard. Too many staff members wade blindly through these documents, believing in their necessity and then maintaining the same level of complexity in all of their work.

Senior staff and managers are obligated to train newcomers to the profession to recognize the limitations of the community’s knowledge about loads, force analysis, stress/deflection predictions and most other aspects of structural behavior. Newly designated “professional” engineers will not truly attain that status until they understand and carry on the tradition of developing good engineering judgment based, at least in part, on these kinds of issues. Three significant figures and an appropriate level of skepticism should regain their status as the standards of our industry.▪ Phillip C. Pierce, P.E., F.ASCE (ppierce@CHAConsulting.com), is a Senior Principal Engineer with CHA Consulting, Inc. in Albany, New York.

Structural Forum is intended to stimulate thoughtful dialogue and debate among structural engineers and other participants in the design and construction process. Any opinions expressed in Structural Forum are those of the author(s) and do not necessarily reflect the views of NCSEA, CASE, SEI, C 3 Ink, or the STRUCTURE® magazine Editorial Board.

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January 2015