STRUCTURE magazine September 2019 by structuremag

STRUCTURE SEPTEMBER 2019

NCSEA | CASE | SEI

Concrete

INSIDE: Consistency is Key

Lower Carbon Footprints Reinforced Concrete Construction Prescriptive Performance-Based Design

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LeMessurier Calls on Tekla Structural Designer for Complex Projects Interoperability and Time Saving Tools

Tekla Structural Designer was developed specifically to maximize collaboration with other project parties, including technicians, fabricators and architects. Its unique functionality enables engineers to integrate the physical design model seamlessly with Tekla Structures or Autodesk Revit, and to round-trip without compromising vital design data. “We’re able to import geometry from Revit, design in Tekla Structural Designer and export that information for import back into Revit. If an architect makes geometry updates or changes a slab edge, we’ll send those changes back into Tekla Structural Designer, rerun the analysis and design, and push updated design information back into Revit.”

Tekla Structural Design at Work: The Hub on Causeway

For over 55 years, LeMessurier has provided structural engineering services to architects, owners, contractors, developers and artists. Led by the example of legendary structural engineer and founder William LeMessurier, LeMessurier provides the expertise for some of the world’s most elegant and sophisticated designs while remaining true to the enduring laws of science and engineering. Known for pushing the envelope of the latest technologies and even inventing new ones, LeMessurier engineers solutions responsive to their clients’ visions and reflective of their experience. An early adopter of technology to improve their designs and workflow, LeMessurier put its own talent to work in the eighties to develop a software solution that did not exist commercially at the time. Their early application adopted the concept of Building Information Modeling (BIM) long before it emerged decades later. While LeMessurier’s proprietary tool had evolved over three decades into a powerhouse of capability, the decision to evaluate commercial structural design tools was predicated on the looming effort required to modernize its software to leverage emerging platforms, support normalized data structure integration and keep up with code changes. After a lengthy and thorough comparison of commercial tools that would “fill the shoes” and stack up to the company’s proprietary tool, LeMessurier chose Tekla Structural Designer for its rich capabilities that addressed all of their workflow needs. According to Derek Barnes, Associate at LeMessurier, ” Tekla Structural Designer offered the most features and the best integration of all the products we tested. They also offered us the ability to work closely with their development group to ensure we were getting the most out of the software.”

One Model for Structural Analysis & Design

From Schematic Design through Construction Documents, Tekla Structural Designer allows LeMessurier engineers to work from one single model for structural analysis and design, improving efficiency, workflow, and ultimately saving time. “Our engineers are working more efficiently because they don’t need to switch between multiple software packages for concrete and steel design. Tekla Structural Designer offers better integration of multiple materials than we have seen in any other product,” said Barnes. LeMessurier engineers use Tekla Structural Designer to create physical, information-rich models that contain the intelligence they need to automate the design of significant portions of their structures and efficiently manage project changes. TRANSFORMING THE WAY THE WORLD WORKS

“Tekla Structural Designer has streamlined our design process,” said Craig Blanchet, P.E., Vice President of LeMessurier. “Because some of our engineers are no longer doubling as software developers, it allows us to focus their talents on leveraging the features of the software to our advantage. Had we not chosen to adopt Tekla Structural Designer, we would have needed to bring on new staff to update and maintain our in-house software. So Tekla Structural Designer is not just saving us time on projects, it is also saving us overhead.

Efficient, Accurate Loading and Analysis

Tekla Structural Designer automatically generates an underlying and highly sophisticated analytical model from the physical model, allowing LeMessurier engineers to focus more on design than on analytical model management. Regardless of a model’s size or complexity, Tekla Structural Designer’s analytical engine accurately computes forces and displacements for use in design and the assessment of building performance.

“Tekla Structural Designer offers better integration of multiple materials than we have seen in any other product.”

Positioning a large scale mixed-use development next to an active arena, a below grade parking garage, and an interstate highway, and bridging it over two active subway tunnels makes planning, phasing and engineering paramount. Currently under construction, The Hub on Causeway Project will be the final piece in the puzzle that is the site of the original Boston Garden. Despite being new to the software, LeMessurier decided to use Tekla Structural Designer for significant portions of the project. “Relying on a new program for such a big project was obviously a risk for us, but with the potential for time savings and other efficiencies, we jumped right in with Tekla Structural Designer. It forced us to get familiar the software very quickly.” “Tekla Structural Designer allowed us to design the bulk of Phase 1 in a single model,” said Barnes. The project incorporates both concrete flat slabs and composite concrete and steel floor framing. “Tekla Structural Designer has the ability to calculate effective widths based on the physical model which is a big time saver,” said Barnes. “On this project, the integration with Revit, along with the composite steel design features enabled us to work more efficiently. Adding the ability to do concrete design in the same model was a bonus because we had both construction types in the same building.” “Tekla Structural Designer helped this project run more efficiently, and in the end it was a positive experience,” said Blanchet.

“Tekla Structural Designer gives us multiple analysis sets to pull from, which gives us lots of control. Most programs don’t have the capability to do FE and grillage chase-down. For the design of beam supported concrete slabs, Tekla Structural Designer allows us to separate the slab stiffness from the beam stiffness, so if we choose to we can design the beams without considering the influence of the slab. In the same model we can use a separate analysis set to review the floor system with the beams and slab engaged,” said Barnes. Barnes also shared similar benefits with concrete column design. “Tekla Structural Designer does grillage take-downs floor-by-floor, finds the reactions and applies them to the next floor. This allows us to view column results both for the 3-dimensional effects of the structure as a whole and from the more traditional floor-by-floor load take-down point of view. Doing both has always required significant manual intervention, but Tekla Structural Designer puts it all in one place.” “We reduce the possibility for human error because with Tekla Structural Designer less user input is required,” said Barnes. “Tekla Structural Designer automatically computes many of the design parameters, such as column unbraced lengths. The assumptions made by the software are typically correct, but we can easily review and override them when necessary.”

“Tekla Structural Designer provided the best fit for our workflow compared to other commercially available software.”

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In the July 2019 issue of STRUCTURE, the Professional Issues column (page 26) incorrectly stated that the magazine was jointly launched by NCSEA, SEI, and CASE in 2006. A more accurate statement would be: “Since the creation of the three major U.S. structural engineering organizations, NCSEA, SEI, and CASE have informally collaborated on various issues. In 1998, they reached agreement on joint editorial production of STRUCTURE magazine, which NCSEA had launched in 1994, as well as additional distribution to all CASE and SEI members.”

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Contents SEPTEM BER 2019

Cover Feature

Consistency was a key driver in the New Science Center at Amherst College. Designers

28 CONSISTENCY IS KEY

embraced cast-in-place concrete as an aesthetic for the project. Much of the concrete would be

By Adam P. Blanchard, P.E.

visible and demanded consistency in color, texture, and finish. Cover graphic courtesy of Payette.

Columns and Departments 7

Editorial Confidential Reporting on Structural Safety

Northridge – 25 Years Later Prescriptive Performance-Based Design

By Glenn R. Bell, C.Eng, P.E., and Andrew Herrmann, P.E.

By David Mar, S.E.

Structural Testing Testing Anchors in Cracked Masonry By Natasha Zamani, Ph.D., P.E.

Business Practices Developing Great Relationships with Other People in the Company

Code Updates ACI Releases ACI 318-19

By Jennifer Anderson

By Jack P. Moehle, Ph.D., P.E.

43 16

Structural Sustainability Performance Concrete

Spotlight The Polynesian Cultural Center Renovation By James M. Williams, P.E., C.E., S.E.

Specifications for Lower Carbon Footprints By Donald Davies, P.E., S.E., Alana Guzzetta, P.E., and Ryan Henkensiefken, P.E.

Structural Forum Role and Responsibility By Roumen V. Mladjov, S.E., P.E.

Structural Practices Recommendations for Structural Grouting By Dan Mullins, P.E.., S.E., and Dan Parker

Construction Issues Recommended Details for Reinforced Concrete Construction – Part 4 By David A. Fanella, Ph.D., S.E., P.E., and Michael Mota, Ph.D., P.E., SECB

In Every Issue 4 40 44 46 48

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

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

S E P T E M B E R 2 019

A Powerful Software Suite for Detailed Analysis & Design of Reinforced Concrete Structures

EDITORIAL Confidential Reporting on Structural Safety By Glenn R. Bell, C.Eng, P.E., F.SEI, F.ASCE,

and Andrew Herrmann, P.E., F.SEI, F.ASCE, Pres.12.ASCE

ontinuous improvement through sharing lessons from failures, near misses, and similar incidents is critical to any profession or industry. In the U.S. structural engineering community, we have long used publications, conferences, and university curricula for this purpose. However, we now have a new, robust tool for learning from failures through the recently launched system Confidential Reporting on Structural Safety in the US (CROSS-US).

The CROSS System The CROSS system was established in the UK in 2005. Fashioned after the U.S. Aviation Safety Reporting System (ASRS) developed by NASA, CROSS is a system where “concerns, incidents, and near misses” of structural “failures” can be reported confidentially. These include pre-cursors of failures. When received and after depersonalization and de-identification, the reports are reviewed by a panel of distinguished industry experts first for quality and veracity, and then for analysis of lessons learned. CROSS publishes lessons learned in the form of anonymized reports, maintains a website and database of such lessons learned, and periodically publishes newsletters on trending issues. The process maintains confidentiality throughout, including discarding identifying information once the analysis report of the case is prepared. The CROSS website and reports are open and free to all. In the fourteen years since establishment, CROSS has developed and refined its operating procedures to ensure the quality of its work, gained the trust of individuals reporting anonymously, and built a reputation as an invaluable resource based on the quality and integrity of its people. CROSS is a much-used resource that has positively impacted practice in the UK.

The Vision for CROSS International We have much to learn from structural incidents and near misses internationally. Even a casual study of structural failures globally shows similar trends and challenges occur frequently. We repeatedly see mistakes that have led to failures in one country occur years later in another country. In an emerging vision for CROSS International, we will create several CROSS operations in various countries that

share information on a common platform. In addition to CROSS in the UK and the United States, there are now CROSS entities in South Africa and Australia. Germany expects to launch later in 2019.

CROSS-US CROSS-US is an entity of the Structural Engineering Institute of ASCE. It is led by an Executive Committee which reports to the SEI Board of Governors (Table). Established through funding provided by SEI, the long-term business plan as CROSS-US expands is to seek sponsorship from government agencies that have an interest in learning from structural failures. The current CROSS-US Panel, which will evaluate submitted reports and publish CROSS products, is composed of prominent members of the engineering, academic, legal, regulatory, and standardssetting organizations in the U.S. We expect to expand this to about twenty through the addition of other disciplines as CROSS-US develops. The CROSS-US website (www.cross-us.org) went live on July 1, 2019. Information is accessible at no charge. The database can be searched by keywords. You may sign up for email updates. Reports may be submitted to CROSS-US through the link at the bottom of the home page. The website leads report submitters through a simple entry form. Reports need not be long or extensive. Supporting materials, such as photos and figures, may be appended. Once submitted, reports are received through the confidential website by one of the two Directors on the CROSS-US panel; the report is first depersonalized (meaning the name of the report submitter is removed) and then deidentified (meaning information regarding the identity of the project and parties involved with the project are removed). Then the depersonalized and de-identified reports are circulated to the CROSS-US Panel for review and comment based on their area of expertise.

Get Involved

Everyone should have an interest in improving practice through learning from failures and near misses. Visit www.cross-us.org periodically and study case reports and newsletters. Use the information in your organization. And, most important, Table of CROSS-US ExCom. please contribute reports confidentially. If you have Glenn Bell, C.Eng, P.E., F.SEI, F.ASCE, ExCom Chair, Simpson Gumpertz & Heger, Inc. questions or would like to get involved with Andrew Herrmann, P.E., F.SEI, F.ASCE, Pres.12.ASCE, Partner Emeritus, Hardesty & CROSS-US, please contact one of the authors Hanover Consulting Engineers via email addresses.■ Judith Mitrani-Reiser, Ph.D., A.M.ASCE, National Institute of Standards and Technology John Tawresey, P.E., F.SEI, Dist.M.ASCE, Ret. KPFF Consulting Engineers Laura Champion, P.E., M.ASCE, Structural Engineering Institute of ASCE James Rossberg, P.E., F.SEI, M.ASCE, American Society of Civil Engineers Alastair Soane, Bsc, Ph.D., ExCom Advisor, Structural Safety, UK

STRUCTURE magazine

Glenn R. Bell is a Senior Principal at Simpson Gumpertz & Heger, Inc., and President-Elect of SEI. (glenn@cross-us.org) Andrew Herrmann is Partner Emeritus at Hardesty & Hanover, President ASCE 2012, and President SEI 2017. (andy@cross-us.org) S E P T E M B E R 2 019

structural TESTING

Testing Anchors in Cracked Masonry By Natasha Zamani, Ph.D., P.E.

Testing in Cracked oncrete and masonry members can experience cracking due to their low Masonry Members tensile strength. Cracking can occur for a variety of reasons, including loads, shrinkage, With the lack of provisions that would temperature, settlement, or stresses induced account for the impact of cracks on anchor by seismic and wind activity. Figure 1 shows performance in masonry, the Concrete and diagonal cracks in masonry walls caused by an Masonry Anchor Manufacturers Association earthquake. Since cracks can have a significant (CAMA) developed a procedure and a negative impact on anchor performance, the program to test and qualify post-installed assumption that an anchor is situated in a adhesive anchors in cracked masonry memcrack is not conservative, especially during bers. For this purpose, experimental work seismic behavior. For concrete members, Figure 1. Cracking in masonry wall after an earthquake. was conducted using an adhesive anchor building codes require the structural design system with threaded rods (3⁄8-inch and to address the effects of cracks on post-installed and cast-in-place anchors. ½-inch-diameter rod sizes) to perform static and seismic tension tests Anchors must be evaluated and the structural designer must determine in grout-filled concrete masonry unit (CMU) walls. design data. However, for masonry members, there is no provision for considering the impact of cracks on anchor performance. This article Masonry Base Materials presents the results of an experimental program addressing testing and evaluation of anchorage performance in cracked masonry. Running bond grout-filled CMU walls were constructed for this test program at the Hilti Test Laboratory in Irving, TX. Lightweight concrete masonry units conforming to the Standard Specification for Loadbearing Anchor Testing in Cracked Concrete Concrete Masonry Units (ASTM C 90) were utilized for the construction Qualification of post-installed anchors in cracked concrete was origi- of the masonry walls. The masonry walls, approximately 64 inches wide nally introduced by ACI Committee 355, Anchorage to Concrete, as and 56 inches tall, were constructed with a single layer of blocks (8-inch a part of ACI 355.2-01, Evaluating the Performance of Post-Installed x 8-inch x 16-inch nominal dimensions) using Type N mortar cement, Mechanical Anchors in Concrete (effective in January 2002), to address conforming to the Standard Specifications for Mortar for Unit Masonry mechanical anchors in cracked concrete. Subsequently, similar provi- (ASTM C 270), and grout, with Type I Portland Cement, in all block sions were developed in ACI 355.4-11, Qualification of Post-Installed cells conforming to the Standard Specifications for Grout for Masonry Adhesive Anchors in Concrete (effective in August 2011) to address (ASTM C 476). Masonry prisms were assembled and tested throughout adhesive anchors in cracked concrete. the test program to determine the masonry compressive strength. Results To qualify the anchor for use in cracked concrete, ACI 355.2 and ACI of the prism compression tests are summarized in Table 1. 355.4 specify three types of tests to be performed in cracks: The first test type is a static tension loading of an anchor in 0.012- and 0.020-inch-wide Crack Generation cracks. The second test type is a reliability tension test performed to evaluate the performance of anchors located in cracks whose opening width To validate the test results, and to simulate possibly unfavorable field is cycled (i.e., the crack-opening width varies cyclically). The third test conditions, the crack width must be roughly constant over the depth of type is an optional seismic test of an anchor in a 0.020-inch-wide crack. the masonry member. Furthermore, the crack must run approximately A hairline crack (width < 0.002 inch) is first initiated to test anchors perpendicular to the surface of the test member to ensure that the in cracked concrete members. A hole is then drilled perpendicular to axis of the anchor is in the plane of the crack. the surface of the test member through the crack so that the axis of To form a crack in the masonry members, splitting wedges were used, the anchors is in the plane of the crack. The anchor is installed and consisting of two halves of an expansion sleeve and a wedge. In this set per manufacturer’s specified instructions (MPII). The crack is then method, three or four splitting wedges were used across the width of opened to the specified width, and the anchor is loaded according to the test member. Holes were then drilled through the masonry along the test procedure described in ACI 355.2 or ACI 355.4. a line at the desired crack location. After the expansion sleeves were Only anchors that have met the requirements for use in cracked concrete, in accordance with ACI 355.2 or ACI 355.4, are permitted Table 1. Grout-filled CMU prism compressive strength data. for use in applications where crack development may occur during Material Material Age Average Material Compressive the service life of the concrete. Also, test results provide additional Type (days) Strength (psi) factors that design professionals must consider in their analysis based Prisms 7 1020 on ACI 318, Building Code Requirements for Structural Concrete. Also, anchors that have passed seismic tests are qualified for applicaPrisms 29 1870 tions resisting earthquake loads in geographic regions of moderate or Prisms 43 1970 high seismic risk (Seismic Design Categories C, D, E, or F). 8 STRUCTURE magazine

Figure 2. Generating a crack in masonry members for anchorage testing.

Figure 3. Anchor locations used for testing: 1) cell center; 2) bed joint (or mortar joint).

placed into the holes, the wedges were sequentially hammered into the expansion sleeves until the masonry cracked along the line of the wedges. The crack was then closed by taking out the wedges. Anchors were then installed and the crack was re-opened to the desired width. Two dial gauges were placed on either side of the anchor to measure the crack width. Figure 2 shows the testing set-up used for initiating the crack and opening it to a specific width. Note that reinforcement (less than 1% of the cross-sectional area of the masonry members parallel to the plane of the crack) was used to restrain the masonry wall during the cracking process.

system used threaded rods (3⁄8-inch and ½-inch-diameter rod sizes) to perform the confined static and seismic tension tests. The entire test matrix for the 60 tests is shown in Table 2 (page 10). Test Series 1 and 3 are static and seismic tension tests of anchors installed in uncracked masonry members. Test Series 2 and 4 are static and seismic tension tests of anchors installed in cracked masonry members. Tests were performed at different locations in the CMU wall, including at the bed joint (or mortar joint) and at the center of the block cell as shown in Figure 3. Note that seismic test Series 3 and 4 were performed only on the anchors installed at the mortar joints since it was expected the mortar joint would be significantly affected by a seismically induced crack condition.

Main Parameters and Test Series A total of 4 test series were performed, with each series consisting of 2 to 4 sets (each set includes approximately five individual tests), to test the post-installed adhesive anchor systems in the cracked grout-filled CMU wall. As indicated above, the adhesive anchor

Static Tension Test Results From the confined tension test results, values of the bond stress were derived for various rod diameters, d, and embedment depths, hef.

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Table 3. Results of static pull-out tests.

Test Series Set τb,o,m (psi) COV (%)

Series 1

Series 2

2270

0.86

2210

6.84

2280

1.15

2345

1.81

1765

13.56

1815

11.17

1675

3.43

1825

11.14

Table 4. Experimental results of seismic tension tests.

Test Series

Figures 4 and 5 show the anchor configuration as well as the confined tension test set up. Assuming a uniform stress distribution along the short bond length, the force Ns in the threaded rod is transferred to the masonry over the embedment length, resulting in a mean bond stresses τb,o of: τb,o =

Cyclic Mean Loading Residual Bond Set Part Capacity (psi)

Ns hef .π.d

In this experimental work, two values were A3 Passed 1815 of particular interSeries 3 B3 Passed 1770 est: the Mean Bond Strength ( τb,o,m), and A4 Failed Series 4 the Coefficient of B4 Passed 1450 Variation (COV) of bond strength. COV measures the dispersion of data points in a data series around the mean. It is a useful statistic for comparing the degree of variation. A small scatter indicates that the data points tend to be very close to the mean and each other. A high scatter indicates that the data points are spread out from the mean, and one another. Table 3 summarizes the results of static tension tests for anchors installed at different locations (bed joint and center of the cell) in cracked and uncracked masonry members. In the uncracked condition, the mean bond strength obtained from various test series was in the range of 2,200 to 2,300 psi with a low COV. However, in the presence of a crack, the mean bond strength was reduced up to 26% compared to the uncracked condition, and the COV increased up to 13%. Note that although COV values of test series in cracked masonry were high, they were still in the acceptable range (below 20%) for a valid and reproducible test.

In adhesive anchor systems installed in the masonry members, the load is transferred from the anchor to the masonry material by bond stresses. The bond between the drilled hole surface in the masonry and the adhesive must be reduced when the base material cracks. This condition leads to lower bond stresses compared to that of the uncracked condition, as can be seen from the test results. The large scatter of test results in the cracked condition can be explained by the random flow of the crack around the hole and along the anchor depth; this reflects the reduced performance of the adhesive anchor.

Seismic Tension Test Results Simulated seismic tension tests in cracked and uncracked masonry members were performed according to the procedure recommended by ACI 355.4-11. In this procedure, the anchors under testing are subject to the sinusoid varying loads, as shown in Figure 6, using a loading frequency between 0.1 and 2 Hertz (Hz). After the simulated seismic-tension cycles were run, the anchors were tested to failure to obtain the mean residual tension capacity. It should be noted that some anchors in set A4 (3⁄8-inch anchors in the cracked condition) failed before the completion of the seismictension cycles. For those that did not fail, their residual strength was found by testing them to failure under consistently increasing load. Table 4 summarizes the ultimate bond capacity of the anchors after completion of the cyclic loading part. In summary, all anchors installed in uncracked masonry members passed the cyclic part of the seismic test. However, in cracked masonry members, the 3⁄8-inch anchor failed during the first sequence of cycling. Tests with the ½-inch anchors in the cracked condition passed the cyclic loading, but bond residual strength was reduced by up to 30% compared to the uncracked condition.

Implications for Design Current guidelines and standards do not take into account the effects of cracking in masonry on anchor performance. Limited test data indicates that there can be a significant reduction on anchor capacity when cracks are present. The design implications of the experimental observations of a reduced strength due to cracking have not been fully identified. More work is required to develop appropriate design provisions in this regard.

Table 2. Overview of parameter combinations used in experimental work.

Test Series

Set

⁄8 x 3 ⁄8

A1 Series 1

Anchor Diameter x Embed Depth (inch) 3

B1 C1

Series 2

Figure 4. Anchor specification.

10 STRUCTURE magazine

Series 3

Series 4

A4 B4

x x x

Seismic

x x

Static

x x

Cell Center

Crack Width (inch)

Testing Type

B2 C2

Bed Joint

D1 A2

½ x 4½

Installation Location

0.012

0.02

Summary In the absence of provisions to account for the influence of cracks on anchor performance in masonry, the Concrete and Masonry Anchor Manufacturers Association (CAMA) has started work to develop a procedure for post-installed adhesive anchor testing and qualification in cracked masonry members. In this regard, an experimental program was performed to examine the possibility of performing tests in cracked masonry and to preliminarily investigate the impact of cracking on anchor performance. In summary, the procedure used in the experimental program for generating a stable crack in grout-filled CMU members and for testing anchors was successful in obtaining valid and reproducible test results. Testing of anchors in cracked masonry was not significantly different from testing in uncracked masonry; however, additional equipment was Figure 5. Example of the confined tension test setup.

needed to form and control cracks. On the other hand, limited data from this testing proved that the performance of the anchor in masonry can be significantly affected by the presence of cracks and should not be ignored.■ Natasha Zamani is the Anchor Approval Engineer for Hilti North America. She is responsible for publishing external evaluation reports such as ICC-ES ESR’s and creating the technical data for the Hilti North America Anchor Products. (natasha.zamani@hilti.com)

Figure 6. Cyclic load amplitude pattern used for seismic testing.

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code UPDATES ACI Releases ACI 318-19 Building Code Requirements for Structural Concrete By Jack P. Moehle, Ph.D., P.E.

he American Concrete Institute (ACI) published ACI 318-19, Building Code Requirements for Structural Concrete, in June 2019. This edition of ACI 318 is the first to be published since the format of ACI 318 was reorganized in 2014. It includes new and updated code provisions as well as color illustrations and interactive links in its online version. ACI 318 includes the requirements for design and construction of structural concrete that are necessary to ensure public health and safety. It also addresses materials that have recently come into common use and incorporates calculations for now-common building types, such as tall structures. Seismic design is extensively addressed in ACI 318-19. The intended user of ACI 318 is the engineer or the building official who is responsible for the contract documents. It is anticipated that ACI 318-19 will be referenced in the 2021 International Building Code (IBC).

Materials Current U.S. building codes limit rebar strength based on decades-old research and the assumption that most reinforcement used in concrete construction in the United States is Grade 60. Progress in metallurgy, however, has resulted in the production of rebar that is almost twice as strong as it was several decades ago. This stronger rebar can transfer much higher stresses; however, it also may lack benchmark properties of weaker steels, such as minimum strain-hardening and elongation. Recognizing these facts, ACI 318-19 includes new requirements for material properties of these higher-strength steels. Accompanying these are myriad changes related to strength reduction factors, minimum reinforcement, effective stiffness, and requirements for development and splice lengths of straight high-strength rebar as well as hooks and headed bars. These updates are expected to support the adoption of high-strength bars, which will, in turn, reduce congestion in heavily reinforced members, improve concrete placement, and save time and labor. ACI 318-19 raises limits on the specified strength of reinforcement in shear wall and special moment frame systems. The new standard allows Grade 80 reinforcement for some special seismic systems and no longer allows Grade 40 rebar to be used in seismic applications. Shear walls can employ rebar in Grades 60, 80, or 100. Special moment frames can use Grades 60 or 80. Hoops and stirrups in special seismic systems used to support vertical reinforcing steel have a tighter specified spacing to prevent the vertical bars from buckling. Shotcrete, a method of placing concrete by projecting it at high velocity, was not explicitly discussed in previous versions of ACI 318 but is now specifically included in ACI 318-19. This effort involved incorporating many IBC shotcrete provisions and updating them to current practice. The unification is expected to clarify both the design process and construction requirements for the use of shotcrete.

Seismic Requirements and PDB With many new metrics for building performance – such as seismic resistance – now in place, performance-based design (PDB) is 12 STRUCTURE magazine

becoming common, especially in the western United States. Performance-based requirements set measurable objectives but allow freedom in design and construction for how the objectives are met. Performance-based seismic design is commonly done ACI 318-19 includes new and updated code using nonlinear dynamic provisions on one-way shear, two-way shear, analysis. A new Appendix A shear wall drift capacity, seismic design, shotcrete, in ACI 318-19 sets param- deep foundations, post-tensioning, precast, eters for design verification durability, lightweight concrete, and more. of earthquake-resistant concrete structures using nonlinear response history analysis. Appendix A is intended to be used in conjunction with Chapter 16 of ASCE/ SEI 7, Minimum Design Loads for Buildings and Other Structures, which includes general requirements, ground motions, and load combinations. Appendix A is also compatible with Guidelines for Performance-Based Seismic Design of Tall Buildings, a document published by Pacific Earthquake Engineering Research (PEER) in conjunction with PEER’s partners in the Tall Buildings Initiative. With the release of ACI 318-19, ACI becomes the primary resource for nonlinear dynamic analysis as it pertains to tall concrete buildings. For the seismic design of structural walls, ACI 318-19 introduces several new design requirements. Whereas previous designs permitted the use of crossties with 90-degree hooks at one end, all crossties for special boundary elements now must have 135-degree hooks at both ends. New provisions also restrict the locations of lap splices near intended plastic hinge zones. Another new design provision provides a check that detailing is adequate for the calculated earthquake displacement demands. Perhaps most significantly, new provisions will now amplify wall design shears based on considerations of wall flexural overstrength and the effects of higher dynamic response modes, which may result in substantial increases in design shears for some walls. ACI 318-19 also adopts the precast concrete diaphragm design procedure of ACI 550.5, Code Requirements for the Design of Precast Concrete Diaphragms for Earthquake Motions. The design method in ACI 550.5 gives designers connection options for selecting the target performance of a precast concrete diaphragm when subject to seismic forces. ACI 550.5 requires that connections be qualified in accordance with ACI 550.4, Qualification of Precast Concrete Diaphragm Connections and Reinforcement at Joints for Earthquake Loading. ACI 318-19 clarifies the application and effect of the vertical ground component on earthquake load. There were numerous clarifications and additions to the requirements for column tie spacing in special moment frames; this included clarifications of tie spacings for columns that are not considered part of the earthquake-resisting system. Intermediate moment frame requirements for tie spacing were also reduced.

ACI 318-19 also made numerous miscellaneous clarifications and simplifications. The column-to-beam flexural strength ratio was adjusted for roof-level connections where the column axial load is low, for example. The shear area of concrete walls, Acv, was clarified so that it is clear it does not include the area of wall openings.

Additional Changes to ACI 318-19

• Updates to STM included the removal of bottle-shaped struts from the code and the inclusion of minimum reinforcing requirements in STM. Other STM improvements included curved-bar nodes and knee joints. Additional changes include: • Shrinkage and temperature reinforcement requirements were simplified. • Load testing provisions were modified to become more consistent with other ACI standards. • Addition of commentary language allowing ACI 318-19 to be used for analysis, repair, and rehabilitation of existing structures and to recognize ACI 562, Code Requirements for Assessment, Repair, and Rehabilitation of Existing Concrete Structures.

ACI 318-19 addresses concerns in the industry that previous shear provisions were inadequate for the design of thick slabs or deep beams. As more large structures are designed to include thick slabs that support upper floors, these updates are timely. ACI 318-19 sections on one-way shear and two-way shear (that is, punching shear) consolidate what was previously a wide range of continued on next page equations They also provide a method to include size effect in shear design to avoid issues wherein increasing a member's size can reduce the design unit shear strength of a section. The new shear equations also allow the design engineer to take the effect of reinforcement ratio into consideration. ACI 318-19 includes revisions and additions aimed at eliminating conflicting provisions in ACI 318, ASCE 7, and IBC regarding the design of deep foundations for earthquake-resistant structures. For some time, these differences have been a source of confusion for both engineers and code officials. The purpose of the code change is to have all the pertinent concrete related design and detailing provisions for Use for all types of concrete and grout applications, from slabs-on-grade to the seismic design of deep foundations containment tanks, multi-story post-tension structures to bridge decks. contained in ACI 318-19. A variety of other industry needs are now addressed in ACI 318-19. Updates were ADVANTAGES made to provisions on post-tensioning, ¡ Maximize joint spacing (up to 300 ft, L/W 3:1) ¡ Enhance compressive and flexural strengths precast concrete, concrete durability, ¡ Prevent shrinkage cracking and curling ¡ Eliminate pour/delay strips lightweight concrete, and strut-and-tie methodology (STM). ¡ Thinner slabs and walls viable ¡ Reduce long-term relaxation of P/T tendons • Post-tensioning updates included and shear wall stresses ¡ Reduce reinforcement requirements clarifications of the construction ¡ Minimize creep and moment requirements regarding loss of ¡ Improve durability and lower permeability prestress, use of a new reference ¡ Minimize waterstops ¡ Increase abrasion resistance 30-40% document for determining prestress losses, deformed and bonded reinforcement spacing limitations, and several clarifications to requirements for anchorage zone reinforcement. • Precast concrete received several clarifications with specific attention on bearing connections. • Numerous changes were made to the durability of concrete sections, including additional requirements for sulfate exposure classes and concrete exposed to water. by CTS Cement Manufacturing Corp. • Lightweight concrete provisions throughout the code received numerous changes and clarificaContact us for more information and project support at 888.414.9043 tions based on the new method CTScement.com for determining λ, the lightweight modification factor.

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Several analysis clarifications and additions were made. Commentary language regarding vibration analysis was added to help the user find guidance for designing a structure when vibrations are design criteria. Calculations of the effective moment of inertia, Ie, were adjusted for nonprestressed reinforced concrete based on more accurate estimated deflection calculation results in both the laboratory and the field.

Code Integration and Reorganization In addition to its compatibility with the ASCE 7 requirements for design verification using nonlinear dynamic analysis, ACI 318-19 achieves code integration by incorporating information from the IBC and modernizing those provisions. ACI 318-19 also identifies areas where personnel are required to be certified and references appropriate certification requirements. By referencing certification requirements directly in the code and commentary, the information becomes more easily accessible to engineers. Two chapters of ACI 318-19 have been reorganized. Chapter 17, which covers anchor design, was reformatted to match the format of other chapters initially adopted for ACI 318-14. It now includes screw anchors and shear lugs. ACI 318.2-14, “Building Code Requirements for Concrete Thin Shells and Commentary,” which replaced ACI 318-11 Chapter 19, was also reorganized to have consistency with the rest of ACI 318-19. Chapter 26, “Construction Documents and Inspection,” has seen significant updates since ACI 318-14. Inspection requirements are unified in this chapter, including the relocation of anchor inspection requirements from Chapter 17. The chapter now recognizes that

projects may have roles for multiple design engineers and provides a framework for their coordination of work. As higher strength concretes have been developed over time, using the standard definition of modulus of elasticity may not be adequate for certain projects (such as tall buildings). Therefore, the definition for modulus of elasticity was updated using data from external documents and best practices. For certain materials that are becoming commonplace in the industry (such as alternative cements, crushed hydraulic-cement concrete, or recycled aggregates), ACI 318-19 Chapter 26 outlines precautions for designers who are considering their use. Additionally, an alternative method for defining λ – which is a modification factor for adjusting tensile strength when using lightweight concrete – was added to ACI 318-19. This new method calculates λ based on concrete mixture proportions, allowing λ to be defined as early as the project design stage. Printed and digital formats of ACI 318-19 are available at concrete.org. Versions are available in inch-pound units and SI units. ACI 318-19 is also available to subscribers of the online ACI Collection of Concrete Codes, Specifications, and Practices. Additionally, the Institute is hosting public and in-house seminars to introduce users to ACI 318-19 – visit the website for locations and to learn more.■ Dr. Jack P. Moehle is the Chair of ACI 318 Building Code Committee and is the Ed and Diane Wilson Professor of Structural in the Department of Civil and Environmental Engineering at UC Berkeley. He is a Fellow of the American Concrete Institute, Structural Engineering Institute of ASCE, and the Structural Engineers Association of California, and is an elected member of the U.S. National Academy of Engineering.

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14 STRUCTURE magazine

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structural SUSTAINABILITY

Performance Concrete Specifications for Lower Carbon Footprints By Donald Davies, P.E., S.E., Alana Guzzetta, P.E., and Ryan Henkensiefken, P.E.

oday, structural engineers are aggressively seeking low-carbon building materials to reduce the carbon footprint of the built environment. Numerous advances in concrete technology are providing solutions in response to these goals and working toward an aspiration of net-zero carbon emissions for future new construction. Even though decades of work have been performed using advances that can move the industry in that direction, they have not always made their way effectively into project specifications. The 2014 update to ACI 318, Building Code Requirements for Structural Concrete and Commentary, moved toward performance-based concrete specifications, which has facilitated the ability to use some of these advances. The design community can utilize the ACI 318-11 code updates to achieve the goal of lower embodied carbon in concrete mixtures. New tools available to the AEC industry, such as the soon to be released Embodied Carbon in Construction Calculator (EC3), are creating new opportunities for specifications that target reduced carbon. The San Francisco airport’s SFO Terminal 1 Redevelopment project provides a case study showing how a performance-based concrete mixture procurement process can lead to lower embodied carbon construction without a significant cost premium. This case study describes how the lessons learned might be applied to other projects.

Low Carbon Concrete Advances Numerous strategies could be implemented on a project to reduce the carbon footprint of concrete. Optimization of the concrete mixture is the obvious starting place. Concrete mixtures can be proportioned to lower carbon in concrete by applying recent ACI 318 updates and incorporating them in project specification requirements.

Supplemental Cementitious Materials Many engineers follow the format of ACI 318 and limit the maximum amount of specific types of Supplemental Cementitious Materials (SCMs) in the specifications, even when the concrete is not in an exposure class F3 environment. Furthermore, these limits are often well below the limits provided in ACI 318. The intention for lowering the limits of SCMs is not to retard the rate of strength gain. Although some SCMs can alter the rate of early-age strength development, readymixed concrete producers can proportion concrete mixtures to achieve the early-age strength requirements, even with cement replacement levels higher than what traditionally thought possible (e.g., 70%). To allow for the highest use of SCMs, designers should work with the contractor’s construction sequencing and specify maximum design strengths at ages later than 28 days whenever possible (as allowed by 19.2.1.3 in ACI 318-14). 16 STRUCTURE magazine

Specifying Proper w/c The water-to-cement ratio (w/c) is historically one of the most commonly specified criteria for concrete and has been tied to the strength of concrete in ACI 318 since 1927. There is a strong correlation between strength and the w/c, with a lower w/c yielding higher strength. When higher strength is achieved by limiting the w/c, especially for locations within a project where it is not always needed, it typically comes at both a higher project first-cost and at a higher carbon footprint than necessary due to increased cement contents. The main concern often expressed by design professionals is the potential of increased drying shrinkage if the w/c is relaxed. This is an appropriate concern in the typical situation where a concrete supplier does not have historical testing data or other means to control the shrinkage properties of the concrete mixtures. A key to any relaxing of w/c without detrimental shrinkage performance is having reliable testing data to support the proposed concrete mixture. Concrete producers with more established testing laboratories and active mixing quality control systems can experiment with material blends regularly to develop supporting data for their high-performing concrete mixtures.

Other Useful Methods Other methods which could lead to a lower carbon footprint include better quality control of the aggregate supply used within a concrete mixture, using strength-boosting admixtures to reduce total cementitious content, incorporating recycled carbon dioxide as a mixture constituent, and using other alternative SCMs such as interground or interblended limestone, silica fume, metakaolin, rice husk ash, and even ground recycled glass powder. It should be noted the mere use of better aggregates, admixtures, other SCMs, or recycled carbon dioxide does not assure a lower overall carbon footprint – transportation, processing, and other pre-chain impacts need to be considered before an actual claim can be made To encourage getting concrete mixtures responsibly but more appropriately specified for their intended strength and durability use, while keeping them financially feasible, Chapter 19 of ACI 318-14 requires the design professional to state the exposure class needed for the concrete. This change, though small, can have a significant impact on what the creator of the concrete mixtures at the batch plant can then do to produce mixes that meet an intended purpose, but with lower overall cementitious material use. In addition to specifying the exposure class, other design professional and contractor requirements are needed to specify the parameters of a concrete mixture fully. These requirements can and typically should include strength gain date limitations, such as 3, 28, 56, or 90 days, shrinkage and modulus of elasticity limitations, pump distance abilities, finishing characteristics, etc.

All these strategies are great to consider. However, the key is to start with directly specifying the performance criteria important to the mixture proportions, and then to let the mix designers determine how to cost-effectively optimize the mixtures to meet these criteria and achieve the lowest carbon footprint.

Magnusson Klemencic Associates, is developing what will also be a free and openly accessible tool titled the Embodied Carbon Construction Calculator (EC3).

Case Study: SFO Terminal 1

The San Francisco International Airport (SFO) Terminal 1 (T1) redevelopment project was an excellent opportunity to test many of the strategies INFO SPECS Environmental product declarations (EPDs) provide a way for a con- identified above. The project started with an owner who, from the outset, FileName:19-1670_Ad_1/2IslandStructure_July_BridgeRepairSolutions Page Size: 5w" x 7.5h" bleed crete supplier to report the environmental performance of a concrete requested the design and construction teams evaluate, monitor, and lower Job#: 19-1670 PR#: N/A Number of Pages: 1 mixture and should follow industry defined Product Category Rules the embodied carbon footprint of the project as an overall objective. Artist: Georgina Morra Email: gmorra@mapei.com Bleed: Yes Amount: .125" 1 1 4 4 E It . Nise like w p o rthe t C nutrition e n t e r D r . label on a (PCR) established for that material. Given that mandate, the design team architect (Gensler), structural engiDeerfield Beach, FL 33442 Date: June 7, 2019 10:29 AM Colors: CMYK Process, 4/0 box of cereal. The first North American version of the PCR for concrete neer (Magnusson Klemencic Associates (MKA)), sustainability consultant O T E : C O L O R S V I E W E D O N - S C R E E N A R E I N T E N D E D F O R V I S U A L R E F E R E N C E O N L Y A N D M A Y N O T M A T C H T H E F I N A L P R I N T E D P R O D U C T. was developed by the CarbonNLeadership Forum (CLF) and adopted (Urban Fabric), and contractor (Hensel Phelps) met early to evaluate lower in 2012. That PCR has been significantly updated since then, and the most current version was released in February of 2019. An example of common language that can be used for requesting EPD’s within a specification can be found from the CLF website at https://bit.ly/2YNowLo. An EPD provides multiple environmental metrics with the most commonly used metric being global warming potential (GWP). The GWP value is useful for demonstrating the reduction in carbon footprint when comparing two concrete mix designs with the same structural performance. When comparing EPDs, an engineer needs to ensure the same PCR version is used as well as considering the whole product life cycle. For example, Central Concrete’s EPDs only consider the cradle-to-grave life cycle; a life cycle analysis encompassing other life cycles stages needs to be considered for comparability. What should a design professional do Carroll Avenue Bridge Takoma Park, MD Corrosion protection with mix specific EPD information? Tools are available from several different Bear Cut Bridge sources and are being further developed Key Biscayne, FL for designers and contractors to utilize EPD data for design and construction decisions. Tally and Athena both use EPD data within their Life Cycle Analysis tools. Since these tools target I-80 Verdi Bridge Verdi, NV design, before specific material suppliers Concrete repair mortars on a project are typically identified, they are restricted to industry average data comparisons for most projects. Climate Earth’s Concrete Selector is available for free to look at the range and average GWP of concrete mixes for a selected strength and cement replacement in their database of concrete mixtures developed using the concrete JEA Northside Generating Station PCR mentioned above. Promising for Jackonville, FL Products for structural strengthening the future and to be released in the fall of 2019, an interdisciplinary team under the umbrella of the Carbon Leadership Forum, with key initial input coming from Skanska, C-Change Labs, and

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Mix design table for SFO Terminal 1.

Member

Nominal f'c *

Max W/C ratio

Shrinkage Max Limit Aggregate Size

GWP**

Quantities Estimate ***

Piles

5.0 ksi @56

0.45

1”

yyy kgCO2

xxx yd3

Pile Caps 6.0 ksi @56 (mix to achieve 75% f’c at 28 days)

0.45

1”

yyy kgCO2

xxx yd3

or Global Warming Potential (GWP) would be a double bottom line decision-making criterion within the project’s material procurement.

Lessons Learned

Building upon the success of the SFO T1, a similar approach was utilized on a campus re-development Spread Footings 4.0 ksi @56 0.45 -1” yyy kgCO2 xxx yd3 project in the Pacific Northwest. For that project, 3 a similar concrete procurement strategy was folBasement Walls 4.5 ksi @56 0.45 -1” yyy kgCO2 xxx yd lowed after a “Low-To-No CO2” concrete strategy Slab of Grade 5.0 ksi @28 -0.040 1” yyy kgCO2 xxx yd3 workshop hosted by MKA to consider what was possible within the Puget Sound regional market. Slab on Metal Deck 4.0 ksi @28 -0.040 ¾” yyy kgCO2 xxx yd3 (120pcy LWC) This included several different architect/engineer/ contractor teams, all working on this re-developShearwalls 6.0 ksi @90 -0.035 ¾” yyy kgCO2 xxx yd3 ment, agreeing to follow the same criteria for their 8.0 ksi @90 -0.035 ¾” yyy kgCO2 parts of the design. The resulting specifications 3 Misc. curbs / mech. pads 4.0 ksi @28 -0.045 1” yyy kgCO2 xxx yd included the latest ACI 318-11 exposure class desTopping slabs exposed to 4.5 ksi @28 -0.040 1” yyy kgCO2 xxx yd3 ignations instead of specifying water-cement ratios, weather and targeted Pacific Northwest concrete durability needs and material opportunities. Furthering a * Dates of acceptance may be adjusted after further concrete supplier and contractor input focus on using EPD’s and embodied carbon data ** GWP = Global Warming Potential, as established by mix specific EPD, provided by concrete supplier to inform an owner decision-making process, this *** Estimated material quantities from Revit model and Tally analysis, TBD, at interim project milestones project is piloting the EC3 tool mentioned earlier embodied carbon alternatives, and to establish targets for where to invest as a case study effort. As a result of this concrete procurement process their efforts. This quickly moved to concrete being one of the critical topics following this performance-based strategy, with a double bottom line to address. A progressive concrete supplier in the area, Central Concrete, consideration of cost and GWP, the winning concrete supplier provided was brought in to consult with the team on opportunities to effectively mix designs that were, on average, 30% below NRMCA industry average lower the carbon footprint of the concrete mixes while maintaining other EPD values and at no cost premium over the competing supplier bids. performance characteristics. That effort led to the creation of the Table identifying the characteristics of the project’s concrete. Summary The SFO T1 project saw embodied carbon reductions within the project materials across the board, with the concrete supply as one of the leading The goal of this article was to supply actionable information to assist areas. A project concrete embodied carbon reduction of 40% (as compared building designers in seeking out lower-carbon alternatives for concrete to NRMCA benchmark EPDs) was achieved with minimal to no cost on their next project, with a path to successfully include lower-carbon increase through a combination of: specifying performance-based mix alternatives and tools to measure and compare those alternatives. designs that identified criteria the design team was really after, request- The authors believe by starting a collaborative discussion with their ing mix specific EPDs, and letting it be known the embodied carbon ready-mix partners, along with partners from the rest of the design and construction teams, a project can achieve a lower carbon footprint, at lower firstB a sis o f D esig n cost, while maintaining and often 1 improving the structural perforSFO – T1 mance of the concrete.■ ADVERTISEMENT–For Advertiser Information, visit STRUCTUREmag.org

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Donald Davies is the President of Magnusson Klemencic. Donald is also a founding member of the Carbon Leadership Forum and an industry champion of the soon to be released Embodied Carbon in Construction Calculator (EC3). (ddavies@mka.com) Alana Guzzetta is the Laboratory Manager of U.S. Concrete’s National Research Laboratory in San Jose, CA. She is the Vice President of the ASCE San Jose Branch and is an active member of ACI and the Carbon Leadership Forum. (aguzzetta@us-concrete.com) Ryan Henkensiefken focuses on collaborating with designers to understand the unique challenges on building projects and advise on solutions to meet those needs. (ryan.henkensiefken@basf.com)

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structural PRACTICES Recommendations for Structural Grouting By Dan Mullins, P.E.., S.E., and Dan Parker

tructural grouting is an integral part of precast concrete, steel, and tilt-up construction. Currently, there are no requirements in building codes or standards for the installation or special inspection of grouted joints. The lack of attention to the timeliness of structural grouting has led to structural failures in both precast concrete and steel-framed structures. On October 10, 2012, a six-story precast parking structure in Miami, Florida, was under construction when a portion of the garage collapsed. The collapse killed four and injured three others. The collapse was caused, as reported by the Occupational Safety and Health Administration (OSHA) Construction Incidents Investigation Engineering Report, “because grout was not placed, as required, at the base of an interior column to adequately transfer the column load to the footing. As loads on the column gradually increased on the day of the incident, the bearing of the column over the shim plates exceeded its capacity, resulting in failure. This triggered a cascade of collapse of columns, inverted tee beams, and double tees on all five floors weighing approximately 3,300 tons over an area of approximately 16,000 square feet.” (Figure 1) On September 3, 2015, a steel-framed structure in Colorado experienced failure because the grout was not placed before significant loads were placed on the structure. A steel column was supported with a steel shim stack on top of a concrete pilaster. The column supported four stories of structural steel framing, and a concrete slab on metal deck had been placed at levels two and three. The concentrated load on the shim stack caused it to punch into the top of the concrete pilaster, resulting in the failure of the concrete and a two-inch drop of the structural frame (Figures 2 and 3). The structure did not collapse but did require extensive repair to lift the building frame to the proper position (Figure 4) and to repair the fractured concrete. Another instance of structural failure due to lack of timely grouting occurred on a precast concrete structure in Colorado. The precast

Figure 2. Protruding anchor rods after shim stack punched into pilaster below the column.

20 STRUCTURE magazine

Figure 1. Aerial view of the Miami parking structure collapse. Courtesy of OSHA.

column had not been grouted when a significant load was placed on it. The result was the shim stack punching into the precast column and causing a localized failure of the column (Figure 5, page 22). These are only a few of the many failures that occur every year due to a lack of timely installation of structural grout or a lack of quality of grout installation. It is clear from these failures that structural grouting is often not given much consideration by specifiers, the timing of grout installation is often not adequately considered by contractors, and the installation is often performed by personnel not explicitly trained to install grout. Grouting is not necessarily a simple process: there are many limitations. Typical limitations include: • Water Requirements – Precise measurements are required for drypack, flowable, and fluid mixtures • Mixing Time – Typically between three and five minutes depending on the manufacturer • Surface Preparation – Substrate temperature must be between 45°F and 90°F prior to grouting. • Grout Temperature – Some manufacturers recommend that grout should be within 15°F of substrate temperature. Cure grout between 45°F and 90°F for a minimum of 24 hours. • Supplemental Materials – Must add pea gravel for wider joints (over three inches for most manufacturers.) It can also be challenging to install grout properly. Obtaining adequate compaction of drypack grout is difficult, especially with narrow joints, deep joints, or limited access. Fluid grout can be equally challenging with required formwork and the difficulty of avoiding trapped air, which prevents solid contact of grout with the bearing surface. To address the gap in building codes and standards, the Structural Engineer’s Association of Colorado (SEAC) Precast Concrete Committee has developed recommended structural grouting practices. This committee consists of representatives of consulting engineering firms; precasters (precast manufacturers, precast specialty engineers, and precast erectors) in Colorado; and the Executive Director of the Precast/Prestressed Concrete Institute (PCI) Mountain States Region. The committee has developed the following suggested practices for the local market to improve the construction practices of structural grouting: • Caution should be exercised when specifying grouting requirements in contract drawings. Language such as “100 percent grouted” or “fully grouted” may result in an effort that is not required by the design or may not meet the

grouted joint detailing requirements. It is recommended that “grout as needed for design” or similar language be used to allow the precaster to define grouting requirements. • Include the following items in specifications for precast projects along with a variant for other trades utilizing grouted joints 1. Submittal of the Grouting QA/QC program that includes the following: a. Temperature of substrates at time of placement and during the curing process as required by the manufacturer Figure 3. Failure of pilaster viewed from below. Figure 4. Apparatus to lift building frame to the proper position b. Grout material technical following failure. data sheet c. Placement procedure d. Placement verification procedure Colorado precasters and PCI have implemented several strategies to 2. Precast installation by a PCI Certified Erector improve the quality of structural grouting. Colorado precasters have 3. Submission of the precaster’s quality monitoring reports to refined their QA/QC programs to ensure grouting is compliant with the owner or design team as requested erection stability plans. Nationally, the PCI Field Safety Task Group recPrecasters should be responsible for establishing the QA/QC program, ommended that all PCI Certified Erectors include, as part of the erector’s including grout design, installation requirements, and verification pro- daily field reports, documentation that identifies each grouted joint and cedures. Each of these steps has an important role in establishing the grout sleeve, the date it was completed, and its location in the building. necessary assurance and documentation as part of a close-out package The PCI Erectors committee is also developing grouting recommendato the design team and, ultimately, the building owner. tions and is working on language to be included in the next edition of the ADVERTISEMENT–For Advertiser Information, visit STRUCTUREmag.org

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PCI Erectors Safety Manual and the PCI Erectors the performance-based path is used, submittal of Manual. It is expected that the recommendations a comprehensive Installation and Quality Control will be similar to those presented above. Plan is required. This plan should include the folSpecial inspection may be utilized to verify the lowing for each type of grouted joint: preparation QA/QC programs are being executed as submitand installation procedures, methods of thermal ted and approved; however, the International control and curing, method of verification of the Building Code (IBC) has no special inspection quality of grouting, size of shim stacks, timing requirements for grouting. If the designer or and sequence of grouting, and qualifications of owner request special inspection services, then the personnel performing grouting operations. special inspection requirements should be fully The prescriptive path of the structural grouting defined by the party requiring the special inspecspecification is required when an Installation tion, including activity, frequency, and location. and Quality Control Plan is not submitted. The SEAC Precast Concrete Committee recThe specification discusses the timing of grout ommends additional review and attention be placement to require grouting before large given to grouting requirements of all structural loads are imposed on the joint, preparation systems to ensure that a proper load path exists of the joint, required formwork, grout mixing, during construction and at ultimate loading. grout placement for dry-packed grout, poured To aid in the application of these recomgrout, and pumped grout, as well as curing and mendations, the SEAC Precast Committee finishing of grouted joints. has developed a guide, Structural Grouting The specification also requires special inspecSpecification, Section 036000. This specification tion of grouted structural joints. For structures includes requirements for structural grouting of erected by PCI certified erectors, special inspecFigure 5. Local failure of the precast column precast concrete joints, steel bearing assemblies, due to lack of grout. tions are recommended to inspect the work and tilt-up concrete joints. The specification procedure for compliance with submitted is written with two separate paths for approval of the grouting pro- Installation and Quality Control Plan. For other systems, special cedures: performance-based and prescriptive. inspections should include a review of the preparation of joints to be The performance-based path is required to be used by PCI certified grouted, mixing of grout in conformance with manufacturer instrucprecast erectors and can also be used by experienced contractors. When tions, the temperature of the air, substrate, and grout, placement of grout and grouting method, curing procedures, and test poured and pumped grout flow rates. Where the placement of concrete slabs, soil, or other construction may conceal joints, joints should be inspected ® before concealment. Prior to placement of concrete slabs supported by a column or wall, inspections should verify that grouting has been completed below the column or wall. The specification intentionally does not indicate the use of grout cube testing per ASTM C109, as the compressive strength of a 2-x2-x2BETTER PERFORMANCE inch grout cube is not representative of the actual strength of a grouted joint. Most grouted joints have a dramatically different aspect ratio and confinement than a 2-inch cube, which significantly increases the grout’s apparent strength. Also, ASTM C109 does not directly apply to pumped or fluid grouts. As such, while testing does indicate the performance of the material relative to the manufacturer’s stated test data and properties, it is not a good representation of in-situ grout strength. Better testing includes destructive testing to confirm the completeness of grout installation and other verification procedures during mixing and placing. The sample Structural Grouting Specification can be reviewed at https://bit.ly/2KymIxK. The SEAC Precast Concrete Committee recommends that practicing engineers, precasters, and contractors remain attentive to structural grouting and review and adapt the sample grouting specification as they see fit. Structural grout is an integral part of the structural system of nearly all structures; improper installation of this material can lead to failures.■

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TIGHTER CONNECTIONS

Dan Mullins is a Structural Engineer with Martin/Martin, Inc. in Lakewood, Colorado. He is a member of ACI Committee 318 (Structural Concrete Building Code), 355 (Anchorage), and 445 (Shear and Torsion). (dmullins@martinmartin.com)

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22 STRUCTURE magazine

Dan Parker is the Director of Client Services with Wells Concrete in Denver, Colorado. Dan is the current President of PCI Mountain States Region and has a seat on the Board of Directors for PCI National. (dan.parker@wellsconcrete.com)

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construction ISSUES Recommended Details for Reinforced Concrete Construction Part 4: Walls

By David A. Fanella, Ph.D., S.E., P.E., F.ACI, F.ASCE, F.SEI, and Michael Mota, Ph.D., P.E., SECB, F.ACI, F.ASCE, F.SEI

This article is the fourth in a series on recommended reinforcement details for cast-in-place concrete construction. Parts 1, 2 and 3 ran in June, July, and August 2019 of STRUCTURE.

Concrete Cover Concrete protection for reinforcement plays an essential role in the requirements of bar spacing and bar development. Reinforcing bars are placed in a concrete member with a minimum concrete cover to protect it from weather, fire, and other effects. Minimum cover requirements for nonprestressed, cast-in-place concrete construction are given in Table 20.6.1.3.1 of ACI 318-14, Building Code Requirements for Structural Concrete. For walls, the concrete cover is measured from the surface of the concrete to the outer edge of the layer of reinforcement closest to the wall surface. Where reveals or rustications run the entire length or height of a wall, the minimum required coverage to the reinforcing bars is indicated in Figure 1. A constant concrete cover is maintained from the inside of the reveal to the surface of the wall. Potential problems can occur where rustications are located in specific areas of a wall. It is

Figure 2. Rustication over a portion of a wall. a) Minimum concrete cover not provided; b) Offset Bars; c) Inner layer of bars.

24 STRUCTURE magazine

Figure 1. Rustication over entire length or height of a wall.

evident from Figure 2a that the cover to the transverse reinforcement is smaller than that which is required. One solution is to offset the reinforcing bars in the localized area to maintain the required cover (Figure 2b). The detailing and placing of the reinforcement can become quite challenging if more than one area of rustication is required or if the rustication is located near an opening in a wall. A more viable solution is to treat the rustication area as an opening and provide an inner layer of reinforcement with the proper cover (Figure 2c). This reinforcement should be developed beyond the rustication area in all directions.

Wall Openings Inevitably, openings of various sizes and shapes for doors, windows, conduit, piping, and ductwork will need to be made in structural walls. Mechanical, plumbing, and electrical openings are usually located just below the slab but, in general, could occur anywhere. Additional reinforcement must be provided around the perimeter of wall openings, commonly referred to as trim bars, opening bars, or corners bars. Section 11.7.5 of ACI 318-14 requires that, for walls with one layer of reinforcement in both the longitudinal and transverse directions, at least one #5 bar must be provided around an opening. Similarly, at least two #5 bars are required around openings in Figure 3. The preferred reference point for walls that have two development length of trim bars. layers of reinforcement in both directions. Longitudinal trim bars around the sides of an opening that run the full height of a wall and that get lap spliced with dowels protruding from the footing should be avoided. Detailing and placing Figure 4. Development length of trim bars measured full-height trim bars from perpendicular trim bars.

Figure 7. Wall corner details that should be avoided – double layers of transverse reinforcement.

Figure 5. Wall corner and intersection details that should be avoided – single layers of transverse reinforcement.

can be a problem because the exact locations of the wall openings may not be available at the time the concrete for the footing is placed; thus, the dowels may not be at the correct location. The preferred reference point to measure the development length of trim bars is at the corner of the opening, as shown in Figure 3. This is an advantageous location for the detailer and placer because it is a fixed point. Measuring the embedment length from a longitudinal or transverse trim bar is frequently done, but the embedment length may wind up being too short if the perpendicular trim bars adjacent to the opening shift for whatever reason from their intended location (Figure 4).

Wall Corners and Intersections Reinforcement at wall corners and intersections need to be carefully detailed to avoid installation problems and more. Long transverse bars with hooks at one or both ends should be avoided because they are challenging to install. Wall bars are often assembled in curtains or mats that are lifted into position. Hooks complicate preassembly, transportation, storage, and handling of the curtains. Constructability is enhanced by providing straight horizontal bars that are lap-spliced together by separate bars; by doing so, adjacent curtains can be installed without interference. Also, the curtains can easily be adjusted to maintain proper concrete cover as the independent hooked bars used for the lap splices are tied in place. The costs associated with the extra reinforcing bars needed for the lap splices are far outweighed by the costs associated with the labor needed for increased handling and installation of the bars with hooks on the ends. Three examples of details at corners and intersections that should be avoided in walls with one layer of transverse reinforcement, because of the reasons noted above, are given in Figure 5. The preferred details are given in Figure 6, which show the separate hooked bars that are dowelled to the straight bars in the wall.

curtains of transverse reinforcement is easy to construct. Figure 8c is also easy to construct for preassembled curtains, but it can only be used in walls that are thick enough to accommodate the width of the U bars (hairpins) at the ends that are lap spliced to the transverse reinforcement in the walls.

(a)

(b)

(c)

Figure 8. Preferred wall corner details – double layers of transverse reinforcement.

The detail in Figure 9 should be avoided at wall intersections for the reasons stated previously. The preferable layouts are shown in Figure 10. Once again, the layout in Figure 10b is only possible in relatively thick walls. Additional recommendations and guidelines for detailing reinforced concrete walls in buildings assigned to any Seismic Design Category can be found in the CRSI publications Design Guide for Economical Reinforced Concrete Structures and Design and Detailing of Low-Rise Reinforced Concrete Buildings.■

(a)

Figure 9. Wall intersection detail that should be avoided – double layers of transverse reinforcement.

(b)

Figure 10. Preferred wall intersection details – double layers of transverse reinforcement. Figure 6. Preferred wall corner and intersection details – single layers of transverse reinforcement.

The details shown in Figure 7 at the corners of walls, with two layers of transverse reinforcement with hooks on their ends, should be avoided because they make it difficult to use preassembled curtains of bars. Of the three arrangements illustrated in Figure 8, Figure 8a is common, but Figure 8b is preferred because the separate 90-degree hooked bars that are lap-spliced with the two preassembled double-bar

The online version of this article contains references. Please visit www.STRUCTUREmag.org. David A. Fanella is Senior Director of Engineering at the Concrete Reinforcing Steel Institute. (dfanella@crsi.org) Michael Mota is Vice President of Engineering at the Concrete Reinforcing Steel Institute. (mmota@crsi.org)

S E P T E M B E R 2 019

2019 STRUCTURAL ENGINEERING SUMMIT DISNEYLAND® HOTEL · ANAHEIM, CA · NOVEMBER 12–15, 2019 GRAND OPENING RECEPTION Tuesday, November 12, 2019, 6:00 pm All attendees invited! Held on the Trade Show floor, this event welcomes attendees to the 2019 Summit, and sets the stage for the networking, education and celebration of the structural engineering profession that will occur over the next four days. Start the event off right with food, drink, and the camaraderie that makes the Summit the unique experience it is.

WELCOME TO CALIFORNIA Tuesday, November 12, 2019, 7:30 pm All attendees invited! The Structural Engineers Association of California (SEAOC) officially welcomes the best and brightest of the nation’s structural engineers to California with a party to celebrate what makes our profession special and what makes California a critical part of the profession. Enjoy the magic of Disney along with a piece of Californian hospitality as you meet new friends and reengage with old ones, celebrating the world we live in and how structural engineers have helped make it.

A CELEBRATION OF STRUCTURAL ENGINEERING Sponsored by Computers & Structures, Inc. Wednesday, November 13, 2019, 7:00 pm Advance ticket purchase required. This extravagant event, hosted by Computers and Structures, Inc., will take place at the Disneyland® Resort. This party will celebrate the immeasurable contributions of the structural engineering profession to society. The evening will feature dinner, champagne, hosted bar, live entertainment, fun, and prizes!

NCSEA AWARDS CELEBRATION Sponsored by Atlas Tube Thursday, November 14, 2019, 6:30 pm Advance ticket purchase required. The 2019 Awards Celebration will put the focus on the awards and award recipients, beginning with a cocktail networking reception. The reception will be followed by a formal Oscar-style presentation of the Excellence in Structural Engineering Awards and the NCSEA Special Awards. Following the awards presentation, attendees will dive into a festive Velvet Rope After Party, with a variety of dinner options, cocktails, entertainment, and music, allowing for opportunities to network with fellow Summit attendees, the Excellence finalists/winners, and recipients of the Special Awards.

The 2019 Summit is Your Opportunity to Mix Fun, Structural Engineering, and the Magic of Disney! Register at www.ncsea.com/register

2019 KEYNOTE PRESENTATIONS Wednesday, November 13, 2019 9:00 AM–10:30 AM A PERSPECTIVE ON THE FUTURE OF CONSULTING ENGINEERS

Have you contemplated the impact that changes in licensure, technology, contracts, and employment trends will have on the business of engineering? Stacy Bartoletti will share some of his thoughts and observations based on his role as a structural engineer, business leader, professional organization leader, and founding member of the Engineering Change Lab USA which is dedicated to this topic. Stacy J. Bartoletti, S.E., is the Chairman and Chief Executive Officer of Degenkolb Engineers. He is a registered structural engineer in multiple states, and an active member of numerous professional organizations.

10:30 AM–Noon TALK NERDY TO ME: SCIENCE NOT COMMUNICATED IS SCIENCE NOT DONE This presentation will motivate listeners on the importance of communication to the success and advancement of their technical work in structural engineering. Melissa Marshall will explore how effective communication is the linchpin between technical innovation and those that are in a position to advance structural engineering and the built world. Melissa Marshall is the founder of Present Your Science, a consulting company that provides on-site group workshops, conference sessions, and 1:1 coaching.

Thursday, November 14, 2019 9:00 AM–10:00 AM THE POWER OF CONNECTION

Nearly one billion people around the world do not have safe access to critical resources like health care, education, or employment due to impassable rivers. Bridges to Prosperity has positively impacted the lives of over one million people in 22 countries by providing safe access to the world’s rural last mile. CEO, Avery Bang, will speak about her personal journey of finding a passion in solving this global issue. Avery Bang, Ph.D., is the President and CEO of Bridges to Prosperity, a nonprofit organization that provides isolated communities with access to essential health care, education, and economic opportunities by building footbridges over impassable rivers.

10:10 AM–11:10 AM MOVING BEYOND LIFE SAFETY FOR COMMUNITY RECOVERY

The current building code is based on the premise that the role of government and codes is to protect the lives of its citizens but that economic decisions for performance above life safety falls to the building owners and developers. This talk will explore the economic risk, how progress is and is not being made in California, and the social tools necessary to protect the economy in the inevitable future earthquakes. Lucy Jones, Ph.D., is the founder of the Dr. Lucy Jones Center for Science and Society, with a mission to foster the understanding and application of scientific information in the creation of more resilient communities.

Friday, November 15, 2019 8:30 AM–9:15 AM STRUCTURAL ENGINEERING: INDISPENSABLE TO CIVILIZATION  SO WHY DON’T WE HAVE MORE INFLUENCE? WHY DON’T WE MAKE MORE MONEY?

In this presentation, Ashraf Habibullah will emphasize the need for a human engineering-based education (i.e. developing your ability to effectively deal with people) and demonstrate why it is important to cultivate deep personal beliefs, public speaking skills, and familiarity with the arts, human psychology, and human chemistry. Ashraf Habibullah, S.E., is a Structural Engineer and President of the software company Computers and Structures, Inc.

Join Us for Practical Education, Stay for the Magic of Disney NCSEA has secured group rates before and after the Summit (per hotel availability) at the Disneyland Hotel and Disney’s Grand Californian in Anaheim, California. Disney is also offering Summit attendees discounted park tickets, giving you the opportunity to fit in some leisure time. Join us for education and networking, but also for a little fun in the sun! Visit www.ncsea.com to reserve your stay.

Consistency IS KEY By Adam P. Blanchard, P.E.

The New Science Center at Amherst College.

he New Science Center (NSC) at Amherst College in Amherst, prevention of imperfections. Equally as important as deciding critiMassachusetts, has several eye-catching features: from its column- cal appearance aspects of the concrete was the ability to describe the free glass-walled commons space to its rooftop garden, transparent project requirements to the construction team. While the structural lab spaces, and hung atrium corridor and stair. To be certain, these drawings show the concrete thickness, location, reinforcement, and features are striking, clean, and inviting, but there is a common theme even shape, the drawings are an inelegant vessel for describing appearthat bonds all these disparate elements. One might notice that it is ance. It became necessary to prepare a specification for cast-in-place not the building’s highlights that make it functional; the consistency concrete tailored to the project. of the architecturally exposed concrete is key. The concrete specification was broken into several subsections related The Boston-based architectural firm Payette designed the NSC, to the appearance of the concrete: definitions – what did the terms bringing on LeMessurier as the project structural engineer. mean; materials – what was the concrete comprised of; and, execuThe NSC is comprised of four distinct parts: an east bar which houses tion – how was it to be built. offices, laboratories, and common spaces, and acts as a central hub for each of the three distinct departmental pavilions which project Definitions outwards onto the campus landscape, not dissimilar to an airport terminal which shoots off to any number of gates. Specific attention At the NSC, not all concrete is created equal; it was not possible for all was paid by the design team to the consistency of the exposed con- 251,000 square feet of the concrete to be visible, so there was no need to crete surfaces to showcase commonality throughout the four spaces. undertake the effort and expense of treating all concrete as architecturally The project was conceived as a cast-in-place concrete structure, exposed. Further, some of the exposed surfaces were formed, and others which was embraced as a part of the project's aesthetic. The concrete were finished, each requiring their own methods of execution. To describe would be visible throughout the NSC, not which regions needed special attention, and as a feature element but as a backdrop servwhat type of attention, the specification introing to highlight the beyond-the-traditional duced Architectural Concrete Regions 0 through structural design topics of strength and stiff5, which identified areas such as undersides of ness. The first question was, “what should it slabs, concrete columns, and pigmented exterior look like?” The architectural goal was simple: concrete walls and panels. the concrete should be its natural gray, and 1) Architectural Concrete Region 0 (AC-0): it should be the same everywhere with no This is the concrete throughout the project specific preferences beyond that. In short, that is not otherwise specified in regions the goal was the consistency of appearance. 1 through 5 below. In the absence of finishes, concrete is a 2) AC-1: This is concrete consistent with uniquely challenging material from which to AC-0 except requiring surface treatment obtain consistency: so many of its constituafter the removal of formwork. ent parts are regionally variable, the forms 3) AC-2: Undersides of slabs; cast-in-place it touches change its appearance, and the concrete stairs. placement and curing processes can lead to 4) AC-3: Vertical concrete walls. imperfections. 5) AC-4: Concrete columns exposed to view; The process to identify and specify measures excludes other columns. to ensure consistency began with research into 6) AC-5: Exterior concrete walls at loading many of the American Concrete Institute’s dock region; pigmented. guides about materials, placement, forms, Completed slab soffit in lab corridor; the surface is Beyond defining each type of region, the curing, stripping, finishing, protection, and formed with HDO plywood. Courtesy of Payette. locations needed to be delineated as well. To 28 STRUCTURE magazine

do that, Payette provided key plans that were inserted in the cast-inplace specification.

Materials

A well-crafted set of drawings and specifications will only get a project so far. The design is only as good as how well it is built. By way of example, the NSC has two adjoining common spaces which are connected by straight runs of cantilevered concrete slabs nearly 300 feet in length. To ensure that the edge of the slab was as straight as possible, the specification adjusted the standard concrete construction tolerances described in the American Concrete Institute’s Specification for Tolerance for Concrete Construction and Materials (ACI 117) by setting a hard limit to the maximum deviation of placement of ¼ inch. Other AC regions were described with a reduction in tolerances

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When considering the appearance of concrete, not only do the constituents contribute but also any other material that contacts the concrete during placement. Of the concrete constituents, no specific preference was given to their makeup other than that the constituents needed to be single-sourced; this requirement was added into the specification directly in several subsections (aggregate, cement, water, etc.). Each level in the NSC is over an acre in area, so each floor plate was completed in multiple concrete placements, with some adjacent slabs being placed more than a month apart. Single-sourcing provided the most reasonable safeguard against adjacent concrete placements having slightly different mixes. In addition to single-sourcing, the specifications required that each type of placement use the same mix design; all slabs needed to contain the same type and quantity of admixtures, as did the columns. Mixes were not required to be consistent between structural elements (i.e., the slab mix was not required to be the same as the column mix). The specification included the following to achieve this: When admixtures or combinations of admixtures are included in Architectural Concrete Regions 1 through 5 as defined above, the admixtures shall each be from a single manufacturer and a single provider to maintain the consistency of placement, finishing, and appearance throughout the project. After the constituents, the specification addressed the materials for formed surfaces which would change the texture of the exposed concrete. The requirements for each type of element (slabs, stairs, walls, and columns) are directly in the specification. For example, the following specification language was added for Architectural Concrete Regions 2 and 4: 1) AC-2 Slabs: High-Density Overlay (HDO) Plywood lined with forms for slab soffits. Joints in forms and plywood panels shall be aligned and placed per the Drawings. Each panel of HDO Plywood shall be used only one time to form the slabs in AC-2; re-use of HDO plywood is not acceptable. Corners at all exposed corners shall be formed with a ¾-inch chamfer strip. 2) AC-4: Custom-fabricated; column forms without seams that result in no expression of form material on the finished concrete surface.

Execution

S E P T E M B E R 2 019

Formwork and HDO panels being placed for architectural concrete.

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such that the concrete placement was 50% more strict than described in ACI 117. As the design progressed, the concrete subcontractor was engaged early to advise on the specification language about which tolerance limitations were practical, at the location where a feature element was being showcased, so that it would not be unduly burdensome or expensive to achieve the design aesthetic. One inherent challenge with an exposed cast-in-place concrete structure is that the concrete is the final visible surface and will be trod upon by the trade workers while the building is fit out, causing inadvertent wear or damage to the concrete. For important architectural concrete surfaces â&#x20AC;&#x201C; such as columns, walls, and exposed slab soffits â&#x20AC;&#x201C; the concrete was protected throughout the remaining construction. For columns and walls, the protection was primarily against striking the surface with equipment or materials, so a wrap was provided at the base to prevent damage. Similarly, the reshoring posts that were used to support architectural concrete were topped with a pad between the post and the slab to prevent dings and scrapes.

30 STRUCTURE magazine

Architectural concrete is protected during the reshore phase to prevent inadvertent damage.

Quality Control A tremendous effort has been undertaken to get to the point of depositing concrete at a project site, including setting shoring, formwork, rebar, spacers, and cleaning the forms. This is a time-consuming, labor-intensive, and often costly procedure. Therefore, the architectural concrete regions must be placed with confidence to ensure the quality of the product; rejecting concrete is likely to have significant cost and schedule implications that ripple through a project until its completion. Steps taken before concrete placement to ensure quality work will pay dividends as construction progresses. For the NSC, the concrete work kicked off with a preconstruction meeting with Amherst College, Payette, LeMessurier, Barr & Barr, S&F, as well as inspection agents and other stakeholders. This meeting acted as a starting point to review the concrete scope and talk with one another about questions, concerns, intents, and goals before the formalities of submittals and RFIs. After the preconstruction meeting, a concrete mockup structure was built, serving as a baseline for levels of acceptance of the architecturally exposed concrete surfaces. The mockup included several of the most challenging construction details (slab elevation changes, rectangular beam framing into a round column, the transition from form liners to traditional forms, and coordinated form tie locations) that might lead to imperfections in the concrete. The mockup allowed the contractor to determine the best method of construction for each of these difficult aspects and allowed the design team to identify achievable surfaces for the architectural concrete versus regions of rejectable concrete surfaces. The most challenging concrete proved to be the placement of the round columns; consolidation and rebar cover were a deficiency in the dedicated mockup, so additional back-of-house locations were found in the main building to gain

further experience with the columns before the architecturally exposed columns were placed.

Key Takeaways There were a few key decisions during the design and preparation of the contract documents for the NSC, which can be grouped into three primary aspects: Research, Specification, and Mockup. The Research component gathered as much information as possible from as many sources as available; find the components of the concrete that can be controlled, ask questions of the teams that will be responsible for constructing them, and determine which of the concrete characteristics are important to the project. The Specification should identify each of the pertinent technical characteristics of the concrete imperative to a successful finished product and describe each in as much detail as possible. Implementing the specification language View of walls in study lounge with aligned View of completed stair with coordinated on a sample Mockup prior to construction on the full project formwork and tie holes. Courtesy of Payette. wall formwork. Courtesy of Payette. will allow the team to understand the project requirements at full scale, practice constructing challenging details, and determine the quality standard for myriad conditions. Project Team Employing these steps early in the process will allow the full project team to come together to deliver a project as successful – Owner: Amherst College, Amherst, MA and consistent – as the New Science Center has been for Structural Engineer: LeMessurier, Boston, MA Amherst College.■ Architect: Payette, Boston, MA Construction Manager: Barr & Barr, New York, NY Adam P. Blanchard is a Principal at LeMessurier and teaches at The Boston Concrete Contractor: S&F Concrete, Hudson, MA Architectural College. (ablanchard@lemessurier.com) CTP HalfPgStruct61819A.qxp_Layout 1 6/18/19 11:59 AM Page 1 ADVERTISEMENT–For Advertiser Information, visit STRUCTUREmag.org

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25 YEARS LATER

Prescriptive Performance-Based Design An Innovative Approach to Retrofitting Soft/Weak-Story Buildings By David Mar, S.E.

ngineers recognize that multi-unit, wood-framed apartment buildings with soft/weak stories are vulnerable to side-sway collapse from earthquakes. The risk was illustrated by the 6.7-magnitude 1994 Northridge quake and the 6.9-magnitude 1989 Loma Prieta quake (Figure 1). In the Northridge quake, for example, roughly 200 such buildings, containing thousands of units, suffered severe damage or collapse. Although California cities aim to improve safety with incentives and mandatory retrofit ordinances, the problem is vast. Reliable design solutions have proved elusive, primarily because these buildings are old, weak, and irregular; they were constructed using archaic materials and outdated practices and, usually, there are no plans. The Federal Emergency Management Agency’s (FEMA) P807, Seismic Evaluation and Retrofit of Multi-Unit Wood-Frame Buildings With Weak Figure 1. Building damaged in 1989 Loma Prieta earthquake. Courtesy of Raymond B. Seed. First Stories, was created to help engineers fix such buildings. The challenge is threefold. First, retrofits must be affordable, which traditionally be considered structurally significant. The building was essentially limits the work to the ground floor to avoid displacing constructed in the 1940s using stucco, lath-and-plaster, and other tenants. Second, rapid adoption is essential given that thousands of contemporary materials; it is unlikely that there is a conventional buildings are affected, so designs should be relatively inexpensive for load path or that any interconnecting metal hardware was used. engineers to perform. Third, solutions must be reliable and effective The upper structure’s strength, in fact, derives from its multiple to justify the massive effort. interconnected nonstructural walls. This capacity is significant, This problem has parallels to the old construction adage: Good, and one of FEMA P807’s innovations is that it brings into retrofit fast, cheap: pick any two. Nevertheless, a team of collaborators and calculations all such walls and their sheathing layers, both structural advisors, under the leadership of the Applied Technology Council, and nonstructural. delivered on all three aspects of FEMA’s design mandate. The team developed guidelines for inexpensive ground-floor retrofits that The Relative Strength Method are easy to design and that perform well. It also created numerous innovative techniques for solving the problems typically associ- Although cost-effectiveness dictates that retrofits be limited to the ated with such work. The result is an approach called Prescriptive ground floor, this strategy poses practical challenges. In response, Performance-Based Design. the team developed the “Relative Strength Method,” which aims to This strategy includes four breakthroughs: 1) utilizing nonstructural optimally strengthen the ground floor – enough, that is, but not so finishes; 2) optimizing the ground-story mechanism; 3) leveraging much that its base-absorption mechanism is compromised. In this extensive nonlinear response-history analyses to predict real building method, the upper stories establish the building’s upper limit of retresults using previously analyzed surrogate structures; and 4) creating rofitted strength, while ground-story retrofits add both strength and and using custom software to find relevant answers quickly. displacement capacity while reducing torsion to the building overall. This solution keeps the retrofitted ground story relatively weaker than the upper structure; that is, the ground story maintains its function Observations and Patterns as a deformation absorption level. Buildings with soft/weak ground floors have two distinct parts. The strong but brittle upper portion, which contains housing units, is Surrogate Structures supported on a weak, brittle, and often torsionally irregular base. As in the damaged apartment building in Figure 1, weak ground floors To prove the robustness of the Relative Strength Method and to may accrue significant damage from seismic forces, with resulting efficiently leverage the power of nonlinear response-history analyses, dramatic displacement or collapse. the team studied an extensive family of surrogate structures. The Nevertheless, the weak ground floor also acts to some extent as a bulk of these were simple four-story nonlinear models with varied base-absorption system, protecting the upper (occupied) floors from parameters for upper-structure strengths, ground-floor weakness, more extensive harm. Note the lack of damage to the upper structure hysteretic behavior (to account for brittleness), and levels of retroin Figure 1, despite that nothing from the second floor up would fit. Once the team had established these parameters, it set out to 32 STRUCTURE magazine

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Probability of Exceedance

Material forms: determine, experimentally, how they all interacted Ductile Brittle (2) total under a variety of scaled earthquake simulations. The simple but powerful idea is that engineers can Upper-story strength ratios, Au: use previous analysis results to evaluate a particular (4) per mat'l form surrogate structure as a means of understanding the behavior of a corresponding real building. 0.1 0.2 0.4 0.6 0.1 0.2 0.4 0.6 Selecting the appropriate surrogate is based on matching key parameters. Engineers can simply borrow the Weak-story ratios, Aw: predetermined analysis results rather than having to 0.6 to 1.1 by 0.1 (6) per upper-story strength ratio Au evaluate each real-world building independently. This works to determine both the original capacity of a structure and to select its optimal retrofit. 11+10+9+8+7+ 6 = 51 Retrofit strengths: To create the surrogate structures, the team started Aw to 1.6 with two broad categories of buildings: one ductile, (51) per upper-story strength ratio, Au one brittle. Each of those two categories had four levels of lateral strength assigned to the upper floors, TOTAL NUMBER OF expressed as percentages of G-forces (Figure 2). Each BUILDINGS: of those upper-floor categories was then assigned six 2 x 4 x 51 = 408 strengths for the weak ground story, ranging from 60 percent to 110 percent of the upper-story strength. Then, each of those weak-story ratios was given various levels of simulated retrofit strengths. There are 612 Time-history (22) Bi-directional records = (44) individual virtual surrogate buildings shown in Figure 2. Each seed records: was subjected to Incremental Dynamic Analyses (IDA) Scaled so that median Sa( T = 0.3 sec ) = 1.0g per the FEMA P695 protocol; these consisted of 22 earthquakes in each of two directions, at 35 inten(35) intensities per seed record varying from 0.1 sity levels. This yielded roughly a million nonlinear to 3.5 by 0.1 response-history analyses. Thanks to these IDAs, engineers can now deterRecover peak interstory 1.0 drift ratios for each mine which intensities of seismic shaking would analysis cause catastrophic damage to a given building. They can also assess what amount of retrofit strengthening Given drift criteria, fit 0.5 achieves maximum benefit. log-normal cumulative density function As noted earlier, this work would be constrained to the ground floor. Over-strengthening the lower stories to the point that the upper structure cannot 0 sustain the transmitted seismic forces entails needless 1.0 (Sa = 1g) 0 3.5 expense and actually reduces the building’s overall Earthquake Intensity capacity, as shown in Figure 3. The vertical axis is Figure 2. The surrogate structures subjected to Incremental Dynamic Analyses (IDA). Spectral Capacity, representing the building’s seismic capacity. The horizontal axis is the ratio of groundstory capacity to upper-story capacity. The families of buildings with is the strongest, with an ultimate lateral capacity 0.6 W (60% of different upper-structure strength are represented by one of four the building’s weight). The Au = 0.1 family, shown with gray lines, colors, noted by Au. The Au = 0.6 family, shown with blue lines, is the weakest. The lines of each family are anchored with their unretrofitted capacity, noted with the coefficient Aw, representing the ground floor strength as a fraction of the upper-structure strength (Au). Aw = 0.6 corresponds to an unretrofitted structure with a ground floor that is 60% as strong as the upper structure. Demos at www.struware.com Each subsequent point on the line represents an additional level Wind, Seismic, Snow, etc. Struware’s Code Search program calculates these and of retrofit strength that would result from adding more plywood other loadings for all codes based on the IBC or ASCE7 in just minutes (see online shear walls or steel moment frames to the ground floor. video). Also calculates wind loads on rooftop equipment, signs, walls, chimneys, Figure 3 reveals a “sweet spot” of optimal strength. It applies trussed towers, tanks and more. ($250.00). to any family of upper-story strength Au, and any level of initial CMU or Tilt-up Concrete Walls Analyze solid walls for out of plane loading and ground story weakness Aw. The optimal ratio of ground-story panel legs next to or between openings by automatically calculating loads to the wall leg from vertical and horizontal loads at the opening. ($75.00 ea) strength to upper-structure strength, for four-story buildings, is roughly 1.33 or 4/3. (The optimal capacity is reached when the Floor Vibration Program to analyze floors with steel beams and/or steel joist. Compare up to 4 systems side by side ($75.00). relative demands on the ground story and the second story are the same.) The ground story carries four levels and the second Concrete beam/slab Program to provide bending, shear and/or torsional reinforcing. Quick and easy to use ($45.00). story carries three levels. When the strength ratio is less than 4/3, the ground story is the weak link in the chain, where the story

34 STRUCTURE magazine

Figure 3. “Sweet Spot” based on analysis results for all surrogate structures.

mechanism will occur. When the strength ratio is greater than 4/3, the second floor is the weak link, and the loads flow through the ground story and damage the second story.

Nuts and Bolts FEMA P807 is a practical tool to determine how strong a given building is, both before and after retrofit, by evaluating a few key

parameters. Using these parameters, engineers can compute the optimal retrofit so that a building absorbs and filters seismic forces at the ground level, without transferring so much of those forces upward that they would either damage the higher floors or necessitate the costly retrofitting of them. The critical structural coefficients are the following: • Ground-story strength • Upper-story strength • Upper-to-ground story strength ratio • Coefficient for Strength degradation • Coefficient for Torsional imbalance On the capacity side, engineers can tap into the previously performed analyses using simple formulas. On the demand side, USGS maps are used to determine the short period demands for the Maximum Considered Earthquake (MCE) hazard (2% chance of exceedance in 50 years). Calculating the key parameters means finding the strength at each story. This is conceptually simple, but it requires pushover analyses (Figure 4 , page 36). This is a departure from traditional design for several reasons. First, as noted previously, all sheathing is counted, in both structural and nonstructural elements. Omitting walls or finishes is not conservative. Furthermore, capacities can be assessed only by adding pushover curves for the walls since different sheathing elements reach peak capacity at different displacements. The parameter for the Strength Degradation, Cd, is based on the shape of the ground-floor pushover curves. Finally, the torsional coefficient

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shear force



drift ratio

Wall line: 1

 2

Peak strength of the first story

First story translational load-dritf curve in the y-direction, F



Drift ratio at peak strength

Figure 4. Adding wall pushover curve to find the story pushover curve and peak strength.

is derived from the ratio of torsional strength demand to that of torsional capacity. It is essential to note that the parameters are all based on expected strengths. Moreover, unlike traditional design, stiffness does not affect the results because the behavior is dominated by the strengths in the nonlinear region of the building’s response.

Software to Keep It Simple

a graphical spreadsheet that simplifies adding walls and generating pushovers. To find any wall capacity, engineers can create the wall assembly using drop-down menus to account for all the elements of exterior and interior walls – stucco, horizontal  wood siding, drywall, and so forth. Next, engineers can draw the walls on the graphical spreadsheet 4 (Figures 5 and 6 ). The software will superimpose the pushover curves for the various walls. When all the walls are drawn, and everything is figured in, the engineer has not only all the story strengths but also values for the overall strengths, the strength degradation coefficients, Cd, and the torsional demand and capacity. Once the engineer has used the WST’s pushover features to determined capacities, he or she can determine the demands (Sm for the Maximum Considered Event (MCE)) by inputting the building’s zip code. If the real-world building turns out to be strong enough, retrofitting will be unnecessary; if it is not, the WST indicates the strength required to yield the optimal retrofit. The retrofits would be composed of either new structurally-sheathed walls (plywood or oriented strand board [OSB]), or new steel moment frames. These elements are expected to yield and go well into the nonlinear range during a major earthquake. As such, capacity design needs to be employed for the collectors, the members, and the foundations. The capacity of new elements (walls and frames) are input using backbone curves that reach ultimate values. For frames, the engineer can input custom backbone curves. Simpson Strong-Tie also has software for their Strong Frame that has been integrated with the WST. The results, before and after retrofit, are expressed in probabilistic terms. For example, a building may have a 90% chance of exceeding its dangerous drift threshold during the MCE. After retrofit, the improvement may be expressed as achieving only a 16% chance of exceeding the drift threshold. This sets up a useful conversation between engineers and stakeholders, capturing the benefit in real terms rather than with the abstract concept of being code compliant or not.

Shake Table Validation

Creating pushover results without automation is challenging given that multiple walls are involved. The Weak-Story Tool (WST) is

Two different retrofit designs, based on the Relative Strength Method and FEMA P807, were validated on a shake table at the University of California San Diego as part of the Network for

Figure 5. Walls of Level 1 in the Weak Story Tool’s graphical spreadsheet.

Figure 6. Walls of Level 2 in the Weak Story Tool’s graphical spreadsheet.

36 STRUCTURE magazine

to the unretrofitted condition, where it collapsed under intense shaking.

Conclusion

Figure 7. Shake table testing at UC San Diego, as part of the NEES-Soft program.

Engineering Simulation (NEES)-Soft program (Figure 7 ). One design featured cross-laminated timber (CLT) shear walls; the other featured Simpson Strong Frames. In both cases, the fourstory retrofits performed well. Deformations occurred primarily at the ground story, with little damage to the upper structure. After the successful tests with the retrofits, the structure was restored

Following the Northridge and Loma Prieta earthquakes, and in anticipation of potentially greater quakes to come, California and other states have undertaken plans to strengthen vulnerable weak/ soft-story buildings. FEMA P807 offers a practical approach to cost-effective retrofits. Prescriptive Performance-Based Design, coupled with the Weak Story Tool software, should ideally simplify and expedite the evaluation and retrofitting of wood-framed, weak-story buildings throughout the region. What’s important – and new, resulting from the Incremental Dynamic Analyses – is that, for these buildings, engineers and stakeholders can now discover the level of earthquake intensity that will cause catastrophic damage or collapse. Moreover, engineers can quantify for clients to what extent investing in a retrofit will reduce these risks.■ David Mar was the Technical Director for FEMA P807. He is a Principal at Mar Structural Design in Berkeley, California. (david.mar@marstructuraldesign.com)

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business PRACTICES Developing Great Relationships with Other People in the Company By Jennifer Anderson

here is something to be said for enjoying the people you work with, especially if much of your waking hours are spent with the people you interact with at work. Conservatively speaking, you likely spend on average 40 hours a week, which equates to about 2080 hours a year, at work. There are 8760 hours in a year, with sleep and work taking more than 50% of your week; that leaves very little waking hours to be spent with other people in your life. So, if you do not have great relationships with your team, a big part of your waking hours are not going to be enjoyable. If that idea does not sound desirable to you, read on for suggestions on how to develop great relationships with other people in your company, your department, or your team.

Assess the Status Quo You need to begin with an assessment of where you are currently at with your workplace relationships. You may have some people you get along with very well, but others you speak to rarely. To truly develop great relationships with other people in the company, start with answering these questions: • How long have you been with the firm? • How many people do you interact with frequently? • Who do you spend the most time with inside the company? • What is the quality of those interactions? • Are you struggling to get along with particular team members and why?

Other People Perhaps there are other people outside your immediate team that you want to get to know better. Do not use the oft said excuse, “I am an introverted engineer,” to avoid those other people. Instead, be thoughtful and purposeful with getting to know people in other teams or departments. People who are successful at companies have a robust internal network; that takes time and effort. To truly develop great relationships with other people in the company, determine what new relationships you would like to forge by answering these questions: • Are there other people in the company you also want to get to know? How have you approached them in the past? • Whom do you know in other departments? How can you strengthen those relationships? 38 STRUCTURE magazine

more about real things – beyond the weather or a TV show – when there is just one other person. When there are a few people at the lunch outing, the opportunity to deepen relationships with others is limited. If you do not believe that, pay attention to what people talk about in the group settings versus in private one-on-one conversations. If you truly want ongoing, sustained workplace friendships and connections, make the continued effort to invite people to lunch. You all have to eat!

Pay Attention to What is Important to Them • What teams do you currently interact with regularly? Are there other people on those teams whom you do not know very well, but deep down you feel you should know better?

Making the Connections The fastest way to start getting to know someone is by just walking up and introducing yourself. However, for all you introverted engineers reading this, you probably just had a mild heart-attack thinking about merely walking up and introducing yourself. So, if that direct tactic does not work for you, try instead to utilize your existing network. Who on your team knows people on other teams? Ask them for help with introductions to new people when you are all attending company-wide meetings or do some blended team lunches. Starting the connection process is not hard; what is more difficult is building sustainable relationships with your peers.

Ongoing Relationships An easy way to think about building relationships is to be honest with how much time you are – or are not – investing in connecting with people. Here is a reasonable equation: 50 work weeks per year x 1 lunch meeting per week = 50 opportunities to deepen current or forge new relationships. Stop going to lunch each week with the same 5 people and talking about the same things. Instead, go to lunch with that group once a month and, during the 3 other weeks of the month, go to lunch with at least one new person per week. One-on-one lunches are some of the best opportunities to really get to know someone. People open up and talk

If you want to develop great relationships with other people in the company, pay attention to what is important to them. Are they married? Kids? Hobbies? Travel interests? Food? Sports? What is their alma mater? Where did they grow up? House projects? Even though we spend a lot of waking hours at work, we all have personal discretionary time, so seek to understand how they like to spend that personal time. Understanding their interests will give you great insights to know more about their complete personality. When people feel like you are genuinely interested in them as a whole person, it is easier for them to open up and reciprocate a friendly working relationship. So, during those one-on-one lunches, get to know their life outside of work so that you have more to talk about than the weather. Ultimately, to truly develop great relationships with other people in the company, you will need to make a concerted effort to get outside your comfort zone. People are usually very kind and responsive when another person reaches out to make an effort to be friendly and forge connections, so be brave enough to introduce yourself. Be brave enough to invite them to lunch and then see how it goes. Do not be surprised if you find yourself with more people to talk to at work, feeling more connected to your team and your firm, and enjoying your work life as a result!■ Born into a family of engineers but focusing on the people side of engineering, Jen Anderson has over 21 years of helping leaders build stronger careers for themselves and their teams. (www.CareerCoachJen.com)

S E P T E M B E R 2 019

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RFEM 5 The 3D FEA Structural Analysis Software The 3D FEA structural analysis software RFEM is the basis of a modular software system. The main program RFEM is used to define structures, materials, and loads for planar and spatial structural systems consisting of members, plates, walls, shells, solids, and contact elements. The add-on modules perform design per the USA, Canadian, and other international standards for various materials and applications. Create a software package specific to your design needs.

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SPOTLIGHT The Polynesian Cultural Center Renovation A Hawaiian Journey

By James M. Williams, P.E., C.E., S.E., AIA, LEED AP

awaii’s number one attraction is the Polynesian Cultural Center, originally constructed in 1963, located in Laie on the Island of Oahu. The north shore of the island can be subject to earthquakes, hurricane winds, torrential rains, and termites. Although the center has been well maintained, it was still in need of significant repairs and renovation work. The renovation project includes; converting a 1989 IMAX theater into a multi-use themed show attraction, repairing and renovating the 24,400-square-foot Gateway Building into a fine dining hall, repairing and strengthening village huts, building a new Samoan Village Chief ’s Hut, and ultimately replacing the marketplace with new restaurants and shops. The conversion of the 30-year-old IMAX Theater included: a new high definition digital projector, a new screen, installing a new suspended floor that could act as a stage, new state of the art action seating, a new catwalk for lighting, custom sound chambers, a themed retail store, lava tube corridors with special effects, and changing the exterior of the building to look like an actual volcano. The exterior volcano cone was created by adding a new, taller, stand-alone galvanized steel tower, which was covered in new reinforced concrete/shotcrete rockwork and waterfalls with integral landscaping. The tower extends above the existing building and cantilevers over it slightly. The tower had to withstand hurricane winds without transferring any load into the existing building. Reinforced grade beams with helical anchors were used to withstand overturning forces. New framing was added to portions of the exterior of the building to support a new rock-work façade. Lower level rockwork is constructed of reinforced concrete that is carved and stained. The higherlevel rockwork is constructed of large foam blocks that are pre-modeled and carved, and then covered and encapsulated with a fireresistant cementitious plaster material that is also stained. The foam is anchored using special adhesives and mechanical fasteners. Entrance and exit corridors were converted into lava tubes using shotcrete. The theater itself appears as a large volcanic chamber with rows of seats stepping down the inner slope of the volcano. The floor supporting the seating was strengthened to support new computerized action seats. STRUCTURE magazine

Two rooms on each side of the theater were converted into large speaker chambers which housed custombuilt subwoofers. These speakers are used to cause the building to “rumble” like a volcano. It was discovered that the speakers could match the natural frequency of the building during specific segments of the newly created digital movie and cause additional unanticipated vibrations in J.M. Williams & Assoicates, Inc. was an Award Winner for its Polynesian Cultural Center Renovation project in the 2018 Annual Excellence in the building. Those frequenStructural Engineering Awards Program in the Category – Forensic/ cies were eliminated from Renovation/Retrofit/Rehabilitation Structures over $20M. the movie, and limitations were placed on the volume controls for the The beams were strengthened using external speakers themselves. post-tensioning to increase the load carrying The existing building footprint is 132 by capacity of the roof to comply with code and 148 feet. The structure is a pre-fabricated to install a new catwalk system. Because of steel building with rigid steel bents spanning the slender nature of the bents, additional 90.75 feet and spaced at 20 feet on-center. web stiffeners and bracing had to be installed 10-inch-deep 14-gage Z purlins span between along the webs and bottom flanges. The CMU the bents and support metal decking and a walls were braced, grouted solid, new conperlite (lightweight concrete) topping. The nections made, and the effective wall heights exterior walls are constructed of 8-inch-thick were reduced, allowing the reinforced CMU concrete masonry units (CMU). The screen walls to act as shear walls and help the bents end of the building extends an additional resist potential lateral loads. 15.5 feet below grade for a total interior wall At the gateway building, termites had height of 70 feet. destroyed all of the perimeter support columns After performing calculations, it was and several beams which had to be repaired discovered that the rigid frames were and replaced. New galvanized steel columns overstressed by 34% per code. The original were used. New entrances were constructed design wind speed was 80 mph (which and the building was themed. was used historically and was based on an Huts had termite damage at all of the perimevaluation of a 1968 study which did not eter columns. The columns were replaced include hurricane data). The 1985 UBC with reinforced concrete which was formed specified a wind speed of 110 mph. The to look like the original natural wood post. current IBC specifies a wind speed of 105 The posts are designed to withstand lateral mph. Because the building has an occupant loads. A new Chief ’s Hut was also load greater than 300, the importance factor constructed to withstand hurricane is 1.15, which requires increasing the design winds and seismic forces.■ wind pressures even more. The design wind pressure was 33 psf; the actual wind pressure James M. Williams is President of AE URBIA varies from approximately 41 psf to 43 psf. aka J.M. Williams and Associates, Inc. a Utah based AE firm. He has served as the President When the gravity dead loads are combined of SEAU and has also served on the Board and with lateral wind loads, the rigid frames are Executive Board of Directors for the TCA. He overstressed 156%. Also, the actual seismic is currently on the AIA’s Codes and Standards base shear is 4 times greater than initially Committee, the IBC General Committee, and designed for and exceeds the base shear due on Task Group 7 of the NGBS. to the design wind load. S E P T E M B E R 2 019

NCSEA

NCSEA News

National Council of Structural Engineers Associations

SEAOSC Responds to Searles Valley Earthquake The Structural Engineers Association of Southern California (SEAOSC) jumped into action in response to the M6.4 and M7.1 earthquakes that took place in Southern California over the July 4th holiday weekend. The organization disseminated several press releases to help inform members and the general public. A team of SEAOSC members also headed to the earthquake area. SEAOSC President Ken O'Dell had arrived from Los Angeles with engineer Martin Hudson and his 25-year-old son, geologist Kenneth Hudson, to assess earthquake damage in Trona and nearby Ridgecrest after massive quakes rocked the region. Their goal was to study the structural damage of the buildings in Trona so they could understand how, exactly, the earthquakes affected those structures and surrounding areas. They stopped Saturday afternoon on California 178, between Trona and Ridgecrest, where the elder Hudson stood on one of the fault ruptures caused by Friday’s magnitude 7.1 quake. “It’s moved everything three feet to the right,” said Hudson, 52, an engineer who forms part of the Earthquake Engineering Research Institute, an organization based in Oakland that brought researchers together in the Ridgecrest area to study the effects of the earthquakes. In the end, the three anticipate that their research could help prevent future building damage during earthquakes. “The goal of our research is to improve the designs of these structures so that they are not as susceptible, and we’re hoping that our work today can contribute to that,” Kenneth Hudson said. SEAOSC President Ken O'Dell also participated in a news conference with Los Angeles County officials and seismologist Dr. Lucy Jones, where they discussed recent seismic activity in the wake of two major temblors in the Mojave Desert and urged Southland residents to be prepared for earthquakes. Learn more about SEAOSC's efforts and view the news conference by visiting bit.ly/seaoscearthquake.

Timber-Strong Design Build Competition Coming to NCSEA Summit In partnership with the American Wood Council, the APA-Engineered Wood Association, and Simpson Strong-Tie, NCSEA is bringing the Timber-Strong Design Build™ to the 2019 Summit in Anaheim, California! In conjunction with the Summit, this “hands-on” opportunity for university engineering students is intended to give real-world experience in both planning and building a wooden structure. Student teams will prepare a project complete with a preliminary design, material cost estimates, structural calculations, and estimated carbon footprint. The activity will provide an opportunity for engineering students to experience the full spectrum of designing and building a real project within a team environment. SEAs can get involved by mentoring and/or sponsoring a team of students from Colleges or Universities in their area. After assembling a team of students and assigning 4 to 5 students as designated builders, the SEA representative would advise the students on project design and offer additional mentoring. Students will be responsible for all of the material costs and their own travel expenses, but the mentoring SEA has the option of offering stipends, grants, or acquiring corporate donations for their team. Learn more and get involved by visiting www.ncsea.com/timber!

Secure Training to Become a Second Responder

Register for the next NCSEA CalOES Safety Assesment Program on Wednesday, October 23, 2019 The California Office of Emergency Services (CalOES) Safety Assessment Program (SAP), hosted by NCSEA, is highly regarded as a standard throughout the country for engineer emergency responders. It is one of only two post-disaster assessment programs that will be compliant with the requirements of the Federal Resource Typing Standards for engineer emergency responders and has been reviewed and approved by FEMA's Office of Domestic Preparedness. Based on ATC-20/45 methodologies and forms, the SAP training course provides engineers, architects, and code-enforcement professionals with the basic skills required to perform safety assessments of structures following disasters. Register by visiting www.ncsea.com. This course is not included in the Live & Recorded Webinar Subscription. Doug Fell, P.E., is a CalOES Assessor, Coordinator, and Instructor. He is a licensed professional engineer (structural) in his home state of Minnesota as well as several others. Doug is the managing principal of Structural Resource Center LLC. His practice includes structural engineering design and analysis for new and existing structures, structural assessments, forensic engineering, emergency response, development and review of safety programs, and project management services. Doug has responded to all types of emergencies and performed assessments all over the U.S. He was the lead structural engineer for the Minneapolis Metrodome roof collapse stabilization and return to service. 44 STRUCTURE magazine

News from the National Council of Structural Engineers Associations

Mix Fun, Structural Engineering and the Magic of Disney

The 2019 Structural Engineering Summit is only two months away! Have you registered or reserved your hotel room? The 2019 Summit is taking place at the Disneyland Hotel in Anaheim, California. NCSEA has secured group rates at the Disneyland Hotel as well as Disney's Grand Californian, and reservations are going quicker than ever. Rooms are available before and after the Summit (per hotel availability), giving you the option to fit in some leisure time. There is a lot to look forward to at this year's Summit! With a brand new format, beginning on Tuesday and ending Friday afternoon, this year's schedule will allow for more education and less overlap. Each day will host at least one keynote speaker, covering topics such as the future of consulting engineers, the importance communication has on success, the economic risk that comes from protecting communities from future earthquakes, the good that comes from connecting populations to important resources, and why structural engineers should develop better interpersonal skills to further their career. © Disney In addition to the 16 hours of continuing education that is available, there are also several networking opportunities to attend. To welcome everyone on Tuesday night, NCSEA will be hosting a Grand Opening Reception for all attendees and then, immediately following that, the Structural Engineers Association of California (SEAOC) is welcoming all attendees to California with their own special event! On Wednesday night, A Celebration of Structural Engineering is back. This extravagant event, hosted by Computers and Structures, Inc., will celebrate the immeasurable contributions of structural engineers. Finally, NCSEA's Awards Celebration on Thursday night will conclude our celebrations for 2019. The newly redesigned event will begin with cocktails and the awards, then will be followed by a festive Velvet Rope After Party with dinner, entertainment, and music, allowing for opportunities to network with fellow Summit attendees, the Excellence finalists/winners, and recipients of the Special Awards. Don't miss this chance to be a part of this growing and dynamic event–join us for the best education with expert speakers, a leading trade show, and compelling peer-to-peer networking at an event designed to advance the industry. Visit www.ncsea.com to view the complete schedule and to register today!

On-Demand SE Exam Review – Study Any Day, Any Time The Best Instructors. The Best Material. Available to you immediately!

NCSEA's SE Refresher and Exam Review course is completely on-demand. Review course materials and watch the recordings when it is convenient for YOU. This on-demand course provides the most economical SE Exam Preparation Course available. The course includes 30 hours of instruction: 9 Vertical Sessions and 11 Lateral. The course will give you preparation tips and problem-solving skills to pass the exam. All lectures are up-to-date on the most current codes, with handouts and quizzes available. PLUS ... students have access to a virtual classroom exclusively for course attendees! Ask the instructors directly whenever questions arise. This SE Exam Preparation Course allows you to study at your pace but with instant access to the material and instructors. Several registration options are available; visit www.ncsea.com to register yourself or to learn more about special group pricing!

NCSEA Webinars

October 10, 2019

September 19, 2019

Howard Birnberg

Before Signing A Design Services Contract

Transitioning Project Managers to Firm Leaders

October 24, 2019

September 24, 2019

Michael Rzeznik, P.E.

F. Dirk Heidbrink, P.E.

Fundamentals of Fire Resistance

Load Testing of Existing Structures

Courses award 1.5 hours of continuing education after the completion of a quiz. Diamond Review approved in all 50 states. S E P T E M B E R 2 019

SEI Update Learning / Networking

Visit SEI at IABSE Congress September 4-6 in New York City NEW ASCE/SEI Prestandard for Performance-Based Wind Design

Now available for free download at https://bit.ly/2ZNnNqu. The Prestandard presents a recommended alternative to the prescriptive procedures for wind design of buildings contained in the nationally adopted standard Minimum Design Loads and Associated Criteria for Buildings and Other Structures (ASCE 7) and in the International Building Code (IBC). It also provides a performance-based approach for wind that is compatible with currently used performance-based approaches for seismic design. Properly implemented, the Prestandard results in buildings that are capable of achieving the wind performance objectives specified by ASCE 7 and, in many instances, superior performance to such objectives. Thank you to the Charles Pankow Foundation for the $150,000 research grant to develop and publish the Prestandard.

NEW Failure Case Studies: Steel Structures

Provides a summary and review of eight steel structure failure case studies designed to promote failure literacy to improve the practice of civil engineering and to reduce risk to the public.

SE Licensure Exam Study Groups

In 2014, the SEI Illinois Chapter in Chicago began discussing hosting a study group or review course for the Structural Engineering (SE) Licensure Exam. Unlike most states, Illinois requires an SE license to seal any structural design plans or calculations. The idea for the study group came from our members. A small group with a focused participant-led format was chosen over a more formal review course or classroom format. Learn more at www.asce.org/SEINews.

Last day to register: September 3 Don’t miss your chance to visit the home of the world’s tallest building and interact with the AEC experts responsible for some of the most challenging civil engineering projects. STRUCTURAL ENGINEERING INSTITUTE

STRUCTURES CONGRESS 2020 St. Louis, Missouri I April 5-8

Sponsor/Exhibit to showcase your brand.

Apply for an SEI Futures Fund Student/Young Professional Scholarship to participate. www.structurescongress.org

SEI Online

Structural Engineering Channel Podcast

Check out recent podcasts with SEI leaders on Base Isolation, Mass Timber, Community Resilience, and more https://engineeringmanagementinstitute.org/tsec-podcast.

Community Resilience in Structural Engineering with Dr. Therese McAllister of NIST

SEI Standards

Visit www.asce.org/SEIStandards to: • View ASCE 7 development cycle

SEI on Twitter

News of the Structural Engineering Institute of ASCE Advancing the Profession

SEI Futures Fund Update

Learn about 2020 funded efforts at www.asce.org/SEIFuturesFund. Thank you, Donors!

Congratulations to the 2019 Jack E. Cermak Medal Recipient Kenny Chung Sau Kwok, Ph.D., University of Sydney

For outstanding contribution to the understanding of wind-structure interaction and its application in wind engineering research and practice, particularly the wind-induced responses and vibration mitigation of wind-excited tall buildings, and the effects of building vibration on occupants.

On Becoming an SEI Fellow By Michele (Mike) Barbato, Ph.D., C.Eng, P.E., F.SEI, M.ASCE

I am extremely honored to become an SEI Fellow and join a group of esteemed colleagues who have been a source of inspiration for my career in Structural Engineering. I have been involved in ASCE and SEI through research, teaching, and service since my days as a graduate student. I view this major accomplishment in my professional growth not as a final destination, but as a new start and an inspiration to be even more active within SEI in the future. Read more at www.asce.org/SEINews. Learn more and Nominate for 2020 SEI Fellows and SEI/ASCE Awards at www.asce.org/SEI.

Students/Young Professionals

Welcome to New SEI Graduate Student Chapters Michigan Technological University and the University of Oklahoma!

Connect with colleagues, take advantage of local opportunities for lifelong learning, and advance structural engineering in your area through SEI Chapters www.asce.org/SEILocal.

Apply for ASCE STAY Grant for Undergraduate Student Outreach

Provides financial support to ASCE groups that successfully propose innovative ways to engage student members with the intent to retain them as life-long, active ASCE members. Grants available $500 - $1,500 for application by ASCE membership communities that show their project forges student-focused relationships with ASCE, strengthens relationships with individual student members, educates students about the benefits of ASCE membership, and builds students’ desire for continued affinity to ASCE. Applications are due September 20. Learn more at https://bit.ly/2ZPhJ10.

Industry Success through Student Involvement By Kevin McMullen, Ph.D., A.M.ASCE, United States Military Academy

The field of Structural Engineering is blossoming with seemingly limitless opportunities to get involved in both the building and bridge design and construction industries. A vast majority of undergraduate students are immediately entering the workforce and significantly contributing to the success of their company’s projects. But the question stands, are we adequately preparing these students for professional success? This is not just a question for educators, but industry leaders as well; it is your company’s success that hinges on the quality of the engineers entering the field. Read more at www.asce.org/SEINews.

Errata

SEI Standards Supplements and Errata including ASCE 7. See www.asce.org/SEI-Errata. If you would like to submit errata, contact Jon Esslinger at jesslinger@asce.org. S E P T E M B E R 2 019

CASE in Point Did you know? CASE has tools and practice guidelines to help firms deal with a wide variety of business scenarios that structural engineering firms face daily. Whether your firm needs to establish a new Quality Assurance Program, update its risk management program, keep track of skills young engineers are learning at each level of experience, or need a sample contract document – CASE has the tools you need! CASE has several tools available for firms to use for recruiting and retaining employees. 962 962-B Tool 2-2 Tool 2-3 Tool 3-2 Tool 3-5 Tool 4-3 Tool 5-1 Tool 5-2

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

ACEC FALL CONFERENCE

ACEC Fall Conference Features Case Risk Management Convocation and More! October 13-16, ACEC is holding its Fall Conference at the Sheraton Grand, Chicago, IL. CASE will be holding their convocation on Monday, October 14. Sessions include: 10:45 am Risk Management -Thinking Past the Contract Speaker: Susan Winslow, Tela Vuota, PLLC 2:15 pm That Means What? Contractual Provisions That May Surprise You Speaker: Robert Hughes, Ames & Gough 4:00 pm Tackling Today’s Business Practice Challenges – A Structural Engineering Roundtable Moderator: Stacy Bartoletti, Degenkolb Engineers The Conference also features: • CEO roundtables; • Exclusive CFO, CIO, tracks • Numerous ACEC coalition, council, and forum events; and • Earn up to 21.75 PDHs

Additional Risk Management Strategies for Bottom-Line Results at ACEC Fall Conference October 13-16

In addition to the CASE sponsored sessions, the ACEC Fall Conference will feature more than 30 advanced business programs, including the following sessions, focused on managing firm liability and risk: Read the Dang Contract T. Wayne Owens, T. Wayne Owens & Associates Beyond Professional Liability: Environmental Health & Safety Risk in the Geoprofessional Community David Duke, S&ME, Inc. BIM for Infrastructure: Are you Ready to Sign and Seal 3-D Deliverables? Will Sharp, Andy Lauzier, Shawn Rodda, and Daniel Prokop, HDR The Conference will also feature: • Robert Costa – National Political Report, Washington Post • Keller Rinaudo – Founder and CEO of Zipline, International • Anirban Basu – Chairman & CEO of Sage Policy Group, Inc. • Sekou Andrews – Creator of “Poetic Voice” and Inspirational Speaker For more information and to register, go to www.acec.org/conferences/fall-conference-2019. 48 STRUCTURE magazine

News of the Council of American Structural Engineers CASE Risk Management Tools Available Foundation 7: Compensation: Prepare and Negotiate Fees that Allow for Quality and Profit

Develop fees based on work effort (task hour) and value to be delivered • Make allowances for unknown conditions • Share the backup for your fee with the client when appropriate • Negotiate based on the scope of work • Be willing to walk away • Do not continue to work for losing clients

Tool 7-1: Client Evaluation

Do you know who your best clients are? Do you know where you should be focusing your marketing and sales efforts to maximize the financial performance of your firm? You may be surprised. This tool will help you answer those questions by analyzing the amount of work and profit for each client.

Tool 7-2: Fee Development

This tool is intended to be used within a consulting firm to stimulate thought and consideration in the development of fees. Engineers in firms that may be experiencing new responsibilities as project engineers and project managers often ask the question – “How do we decide on fees?” This tool may be a useful primer for these employees and lead to further discussion with firm management on the firm’s fee development strategies.

Foundation 8: Contracts: Identify Onerous Contract Language

Negotiate Clear and Fair Agreements • Understand ever-changing contract language and demands • Use a CASE, AIA, or other accepted base contract • Modify the contract for each project, as needed • Use a contract that you can understand • Use the contract to reasonably share project risks • Get a signed contract • Utilize legal review when appropriate

Tool 8-1: Contract Review

Do you (or your legal counsel) review every contract to find onerous clauses? Do you know what they are? Do you always find them? This tool will help you find these clauses or words throughout the document.

Tool 8-2: Contract Clauses and Commentary

This Contract Clause Review and Commentary tool is intended to assist in your review of contracts and potentially alert you to clauses that may be problematic. Although not totally encompassing for all potentially onerous or problematic clauses, this tool highlights several clause types that occur often and may raise concerns.

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

NEW Course! Advanced Skills for Superior Project Managers Challenges, Proficiencies, Techniques

Many project managers step into the PM role and never stray far from the same kind of project, even if they switch firms. While there is nothing wrong with the status quo, it does not encourage professional growth. However, if you are ready to prep your project managers for the next level and get them thinking about big-picture leadership, then read on … Designed to help project managers sharpen their skills with new ideas and techniques, and keep current with the rapidly changing engineering and construction environment, this brand new class, Advanced Skills for Superior Project Managers: Challenges, Proficiencies, Techniques, combines the scheduling ease of video-learning with the immediacy and intensity of a live classroom – all with little or no disruption to billable staff time. This 9-module interactive class begins on September 9 and is limited to 25 registrants. 18+ PDHs offered. Our international faculty of experienced project managers offer diverse perspectives on what it takes to excel in project management. Your PMs will learn how to better manage staff and clients, control scope creep, work abroad, and more! Beginning with a skill level review – including the basic tools and techniques you should already be using – this advanced course moves briskly into the challenges and risks PMs face daily. While this course does build on ACEC’s Laying the Foundation for Superior Project Managers, completion of the previous course is not required. New or aspiring project managers will greatly benefit from the material presented. Help your project managers assess and grow their skills with this flexible, step-by-step course that adapts to their current workload while motivating them to succeed. For more information, go to www.acec.org/education/seminars.

Follow ACEC Coalitions on Twitter – @ACECCoalitions. S E P T E M B E R 2 019

structural FORUM Role and Responsibility

Upgrading Highway Bridge Infrastructure By Roumen V. Mladjov, S.E., P.E.

here is general agreement that the country’s infrastructure is in critical condition. With available funding that pales in comparison to the amount needed, engineers working on infrastructure-related projects have a professional obligation to produce high-efficiency projects to ensure maximum impact is obtained from the available funding. Infrastructure is a very broad term, comprising roads, bridges, tunnels, railroads, stations, airports, seaports, dams, electricity, water and wastewater systems, etc. To analyze the complexity of the problem, consider an area of infrastructure where data is routinely collected and quantified – highway bridges in the U.S. For years, the American Society of Civil Engineers (ASCE) has been monitoring bridges and providing periodic “report cards” on their condition. The National Bridge Inventory also provides yearly information on the status of our bridges. In 2016, there were 614,400 bridges in the U.S. with total a deck area of 371,500,000 square meters (91,799 acres!). 56,000 of these bridges (9.1%) are classified as Structurally Deficient; 84,100 (13.7%) are Functionally Obsolete, or a total of 140,100 (22.8%) of all bridges are substandard. By deck area, the percentage is even higher at 26.5%. All these bridges need to be retrofitted, strengthened, or replaced. This is an enormous task requiring a tremendous amount of money, design, and construction effort. At the current pace, a full replacement or retrofitting of the substandard bridges will require 78 years; this is an unacceptably long period. It is essential to design and build efficient bridges to maximize the available resources (construction materials, labor, etc.) to meet the demand. Project efficiency – defined as saving cost and materials while providing a quality product – has always been very important. Today, given the extreme necessity for replacing or strengthening substandard bridges, the responsibility of engineers to design and build efficient, less expensive structures becomes as essential as life-safety requirements. An efficient project optimizes delivery resources, thus allowing for the repair or replacement of other substandard bridges that may have life-safety issues. 50 STRUCTURE magazine

All engineers involved in bridge infrastructure renovation, from the design engineer and the construction field engineer to their executive managers, from the control-checking engineers to those responsible for planning and accepting projects, and all engineers advising the transportation agencies in the process should strive to provide high level efficient and economic projects. When advising different agencies, engineers should be objective, their position based on facts and numbers, and in no way should these engineers be influenced by the preferences or politics of the agencies soliciting the advice. It is time that agencies allowing substandard projects to be constructed with extraordinary costs (such as the New East Span of the SF-Oakland Bay Bridge built for $6.5 billion over 14 years at four or five times the cost of similar structures) be held accountable. For decades, the construction industry, and specifically planning departments, have used cost for planning, managing, or evaluating projects. Thus higher cost has become a symbol of “better.” As a consequence, a transportation agency may spend several trillion dollars and not solve the core problem – an unacceptable number of deficient bridges. A better criterion should replace measuring achievements in a dollar amount – for example, bridge deck, road, or runway completed per every million dollars spent. This will transfer the emphasis from more expensive to more efficient projects. A more expensive bridge is not necessarily stronger or safer than an efficient, economic bridge built in compliance with the bridge design codes. “The least expensive bridge is the best bridge with all other factors the same” (David P. Billington, Civil Engineering, March 1990). Estimating the efficiency of a bridge structure is complicated because there are no standardized measurements for efficiency. Using dollar cost, steel weight, or concrete per square unit of the project may vary for comparing structures with different spans and configurations. It would help to create a national database of bridges, including cost, steel, and concrete used per unit deck area, with efficiency coefficients (for cost, construction materials, and locality) to evaluate and compare the efficiency level of new projects during their planning, design, and construction phases.

Retrofitting and reinforcing, instead of replacing with entirely new structures, should be considered whenever possible. There are many creative, efficient, and rational methods for retrofitting and reinforcing existing structures being developed by both practitioners and researchers. These new methods may be appropriate to introduce more efficiency into the industry. Transportation authorities can begin this program by scheduling the replacement or reinforcement of substandard bridges with small spans and multiple repetitive applications (which cover probably 80% or more of all substandard bridges). Design and design-build competitions can provide creative ideas for the efficiency of both routine and long-span bridge projects. DOTs can avoid advancing projects with poor efficiency ratings and should consider design competitions for every complex project with higher costs. Everyone should do his/her part to achieve better efficiency – politicians and lawmakers may contribute by finding and allocating the necessary funding in the budgets; engineers, builders, and administrators may contribute by using both proven and new technology to design and build efficient structures, thereby achieving faster infrastructure recovery. It is vital to encourage and award highly efficient structures, while inefficiency should be discouraged. Professional engineering organizations like the National Council of Structural Engineers Associations and the American Society of Civil Engineers have advocated and volunteered to serve a more significant role in the promotion of better, more highly efficient projects. The good news is that there is now a serious call for renovating our infrastructure in general and our highway bridges in particular. This is an excellent opportunity for incorporating innovative structures, using the best solutions for faster, lighter, and more efficient design and construction.■ Roumen V. Mladjov has more than 54 years in structural and bridge engineering, and in construction management; his main interests are structural performance, seismic resistance, efficiency, and economy. (rmladjov@gmail.com)

S E P T E M B E R 2 019

Are You Redi?

REDICOR SIMPLIFIES AND ACCELERATES THE CONSTRUCTION OF REINFORCED CONCRETE CORES. Conventional cast-in-place, pre-cast and masonry methods of constructing reinforced concrete shear cores often require long and expensive Pre-engineered load- schedules bearing structural before connections enable structural framing to begin framing can immediately. begin.

Now there’s a better way. RediCor is a pre-fabricated, ready-to-set modular steel form system that simplifies and accelerates concrete core construction. Our load-bearing modules are ready to set once on-site, and structural framing can be installed simultaneously – saving time, energy and money. Are you Redi? VISIT US AT REDICOR.COM FOR THE REDICOR STORY.

V U LC R A F T/ V E R C O

Powerful Partnerships. Powerful Results.