STRUCTURE APRIL 2020
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INSIDE: Many Glacier Hotel
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High Strength Reinforcement Bond Strength of Adhesive Anchors Building Above Coal Mines
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Contents APRI L 2020
Cover Feature 22 PRESERVING THE MANY GLACIER HOTEL By Ian Glaser, P.E., and Christine Britton, P.E.
The lower of the iconic Hotel stories are concrete, and the upper stories are wood. Steel rod holdowns extend continuously from the top of concrete to the attic level, and collectors were installed at each diaphragm level. Each shear wall was founded on a new concrete grade beam supported by new micropiles.
Columns and Departments 7
Editorial Boost Your Career Plan
24
By Nils V. Ericson III, P.E.
9
By Rahul Sharma, S.E., et. al
12
Underground Coal Mines By Gennaro G. Marino, Ph.D., P.E., D.GE,
Code Updates High Strength Reinforcement for Seismic Applications in ACI 318 -19
and Abdolreza Osouli, Ph.D., P.E.
30
By Linda Kaplan, P.E.
42
By Alexis A. Clark, P.E.
16
for Post-Installed Adhesive Anchors
18
Structural Rehabilitation Adaptive Reuse of the Apex Hosiery Company Building – Part 3 By D. Matthew Stuart, P.E., S.E.
Legal Perspectives Warning Flags for Structural Engineers By Robert Hughes
Structural Practices Federal Changes By T. J. Bland, P.E.
Codes and Standards AASHTO Vehicle Live Loading
Structural Components Beyond Bond Strength of Adhesive Anchors
Construction Issues Building Above
In Every Issue 4 34 36 38 40
Advertiser Index Resource Guide – Engineered Wood Products 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. APRIL 2020
5
A Powerful Software Suite for Detailed Analysis & Design of Reinforced Concrete Structures
EDITORIAL Boost Your Career Plan Do Not Ignore Critical Soft Skills By Nils V. Ericson III, P.E.
D
o not neglect essential business skills that you never learned Financial – How do you manage the increasing popularity of in Engineering School! Today’s EITs, PEs, SEs, and Project subscription-based software licensing models? How do employee Managers are tomorrow’s firm leaders. utilization rates relate to profitability? What are some of the different Staying abreast of code revisions, construction advances, and rapidly fee development strategies used by leading firms? What are the project evolving technology is critical for today’s structural engineer. However, and firm financial metrics you most closely monitor? do you pay the same amount of attention to the development and Human Resources – How do you encourage a culture of inclusion continual maintenance of skills that will be necessary when you are and diversity? How do you develop policies regarding family and medifaced with issues related to firm management and operations? Building cal leave? What is the appropriate (and legal) way to interview, and a foundation of technihow do you standardize your cal expertise is paramount, firm’s interview process? How particularly at the start of do you manage the multitude your career. But do not fail of potential disruptions from It may come as a surprise to some to train that other side of a worldwide pandemic such younger engineers but, not too far your brain, that part that as COVID-19? generates revenue, avoids All of the topics above (and into their career, that they will likely claims, contributes to your more) were discussed in varyfirm’s culture, and weighs ing settings at the Coalition be spending a minority of time on the relative importance of of American Structural quality, client satisfaction, Engineers (CASE) February traditional engineering tasks. employee satisfaction, and Winter Meeting in New firm profitability. Orleans. The most benefiIt may come as a surprise cial environment, perhaps, to some younger engineers is one-on-one informal but, not too far into their conversations between parcareer, that they will likely be ticipants during breaks in the spending a minority of time scheduled program. It is now on traditional engineering easier than ever before to gain tasks. To successfully and profitably run an engineering business, insight and knowledge from respected industry leaders at the CASE engineers need to develop, practice, and train risk management, Winter and Summer meetings. No longer a full day of inclusive human resources, and financial management skills with the same committee planning, these meetings kick off on Thursday with a commitment that they approach technical skills. dinner presentation, generally on a project or issue of local interIf you are a small or medium-sized firm without in-house financial, est. Discussions continue with a half-day of presentations, industry human resources or legal departments, you may not have a sounding roundtables, and expert panels. The remainder of the day is dedicated board to discuss approaches and strategies to address current business to open committee meetings, where you can find yourself discussing practices and risk management issues. How would you like to have an the most pressing issues facing practicing structural engineers with open forum to consider the following example issues facing today’s a group of generally ten or less firm principals and owners. Best project managers, principals, and owners? of all, the meeting is open to engineers of all levels of experience, Recruiting and Retention – Does your firm offer an atmosphere giving younger engineers and project managers unparalleled access and culture that interests and motivates today’s graduates? How do to industry leaders. you keep your staff challenged and engaged enough in engineering, I would also like to invite structural engineers of all experience so they do not consider a move to another industry? What benefits levels to NCSEA’s Structural Engineering Summit in Las Vegas this and creative compensation/benefits packages (beyond salary) do your November. This year’s Summit will include an all-new full-day program competitors use to recruit and retain engineers? What strategies do developed jointly by NCSEA and CASE, The Business of Structural you use for hiring a new employee with salary demands that do not Engineering, focusing on pressing business practices and fit your firm’s compensation structure? risk management issues facing today’s Project Managers Risk Management – How do you prepare project managers to hold and Principals.■ difficult conversations with clients and jurisdictional authorities? What are the contract terms/clauses that raise red flags, and how do you Nils V. Ericson III is a Principal at m2 Structural in Atlanta, Georgia, negotiate those terms with your client? What is the standard of care and the chair of the CASE Programs and Communications Committee. as it relates to delegated design? Do you need a teaming agreement (nericson@m2structural.com) when you are a sub-consultant on a design-build project? STRUCTURE magazine
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High Strength Reinforcement for Seismic Applications in ACI 318-19 By Rahul Sharma, S.E., Kion Nemati, P.E., Jakub Valigura, Ph.D., Nate Warner, P.E., and Catherine Chen, S.E.
A
s buildings get taller, bigger, and are required to resist higher seismic forces, the amount of reinforcement needed becomes impractical. Even if theoretical sizes can be calculated, it may be impossible to construct tightly spaced rebar
cages or congested joint connections. Using higher strength reinforcement is a natural solution to this problem. Research on the use of high-strength reinforcement (HSR) began in the late 1950s. The outcome of this research first appeared in ACI 318-71, Building Code Requirements for Structural Concrete, which allowed limited use of reinforcement with a higher grade than 60 ksi. However, the maximum yield strength of reinforcement in elements resisting seismic loads was limited to 60 ksi. This restriction remained in the building code until recently due to a lack of data on cyclically loaded members with HSR. The main expected advantage of HSR over conventional reinforcement (CR) is a lower volume of reinforcement material in construction, resulting in lower construction time and costs (Price et al. 2013). In 2014, two reports identified experimental tests required and provisions of ACI 318 that would need to be updated to allow the use of HSR in seismic applications (ATC 2014; NIST 2014). Later, extensive research answered many of the identified gaps (the online version of this article includes a summary of this research). This article introduces changes in ACI 318-19 related to the use of HSR and presents considerations engineers should be cautious of before specifying HSR.
Changes Related to HSR in ACI 318-19 In response to the research, ACI 318-19 introduces significant changes allowing more applications of HSR in concrete buildings. ACI 318-19 was released in July 2019 and will likely be referenced in the 2021 IBC. Reinforcement in special lateral force resisting systems, which were previously limited to Grade 60 for flexural, axial, and shear reinforcement, can now use up to Grade 80 or Grade 100 depending on the application. Additionally, various gravity elements, which were previously limited to Grade 80, are now extended to Grade 100. Refer to Table 1 for a summary of major reinforcement grade changes from ACI 318-14 to ACI 318-19.
Reinforcement Specification Requirements These revisions occurred without the introduction of new ASTM specifications for HSR. Despite this, the adoption of higher grades was not independent of new refinements to rebar manufacturing. The ACI 318 Committee chose to address these refinements directly in the code, in Chapter 20, by setting requirements for smoother bar deformation profiles, various minimum strength ratios, and minimum elongations before fracture. For ASTM A706, the requirement on deformation profiles calls for “the radius at the base of each deformation… be at least 1.5 times the height of the deformation.” This requirement is intended to avoid low-cycle fatigue cracks at these locations along the bar and improve the number of half-cycles to fracture. These new provisions apply to ASTM A706 Grade 60 reinforcing as well.
Detailing Enhancements Perhaps the most significant changes to designing with HSR relate to detailing requirements. In past versions of the code, engineers could
use two equations to calculate development and lap lengths. Those two equations remain largely the same except for an added reinforcement grade multiplier (ψg) that is equal to 1.0 for Grade 60, 1.15 for Grade 80, and 1.3 for Grade 100; Example 1 illustrates splice length calculation according to ACI 318-19 with f´c = 6 ksi. Also note that, for lap splices of HSR, the code now requires a minimum amount of splice confinement provided by transverse reinforcement along the splice.
Example 1. Splice Length Calculation Ls (#11, Grade 60, 6 ksi) = 6’-0”*; best case** = 3’-7” Ls (#11, Grade 80, 6 ksi) = 6’-0” x (80 ksi/60 ksi) x (1.15) = 9’-3”*; best case** = 6’-6” Ls (#11, Grade 100, 6 ksi) = 6’-0” x (100 ksi/60 ksi) x (1.3) = 13’-0”*; best case** = 7’-9” *Use of equation in Table 25.4.2.3 (traditionally used by structural engineers for most typical conditions without epoxy coating) **Best case refers to the upper limit where (cb + Ktr)/db = 2.5, in conjunction with Eq. 25.4.2.4a The minimum amount of longitudinal reinforcement for flexural members is inversely proportional to reinforcement yield strength and hence is lower for HSR than for CR. However, 80 ksi is the maximum yield strength permitted to be used in equations in 9.6.1.2, equating minimum reinforcement areas for Grade 80 and Grade 100. For special structural walls, the minimum reinforcement area follows the same pattern, except the steel yield strength is not limited in this calculation (18.10.2.4). The maximum longitudinal reinforcement ratio in special moment frame beams is lowered to 0.02 for Grade 80 reinforcement (18.6.3.1). Tighter transverse tie spacing is required for seismic systems using HSR to inhibit longitudinal bar buckling under higher axial stresses. continued on next page APRIL 2020
9
Table 1. Changes in use of reinforcement grades between ACI 318-19 and ACI 318-14.
ACI318-19
ACI318-14
Maximum fy or fyt permitted Maximum fy or fyt permitted for design calculations, psi for design calculations, psi
Usage
Application
Flexure; axial force; shrinkage and temperature
Special Moment Frames
Flexure; axial force; shrinkage and temperature
Special Structural Walls (2)
80,000
60,000
100,000
60,000
Flexure; axial force; shrinkage and temperature
Other examples: gravity columns, slabs, beams, foundations, etc. (3)
100,000
80,000
Shear
Special Moment Frames (4)(8)
80,000
60,000
Shear
Special Structural Walls (5)(8)
100,000
60,000
Regions designed using strut-and-tie method
Other (except longitudinal ties) examples: strut reinforcement, etc. (6)(7)
60,000
60,000
Reference: ACI 318-19 Table 20.2.2.4(a)-Nonprestressed deformed reinforcement 1. Refer to ACI 318-19 Table 20.2.2.4(a) for a complete list of applications and limitations. 2. All components of special structural walls, including coupling beams and wall piers. 3. Longitudinal reinforcement with fy > 80,000 psi is not permitted for intermediate moment frames and ordinary moment frames resisting earthquake demands. 4. Shear reinforcement in this application includes stirrups, ties, hoops, and spirals in special moment frames. 5. Shear reinforcement in this application includes all transverse reinforcement in special structural walls, coupling beams, wall piers, and diagonal bars in coupling beams. 6. Note that this does not apply to confined regions within strut-and-tie designs. 7. Note that ACI 318-19 now has a section dedicated to seismic applications of the strut-and-tie method. 8. Shear friction applications are limited to an fy = 60,000psi.
The maximum spacing in the plastic hinge region is decreased to 5db for Grade 80 in special moment frames (18.6.4.4 and 18.7.5.3), and to 5db and 4db for Grade 80 and Grade 100, respectively, for special shear walls boundary elements (Table 18.10.6.5(b)). Additionally, stricter limitations exist for the use of mechanical splices of HSR in seismic applications and should be considered early in the design process (18.2.7.2). Headed bar provisions (25.4.4.1) have seen multiple changes, one of which directly applies to HSR. The previous limitation of fy to 60 ksi for the use of standard class HA headed bars has now been removed, opening its application to HSR.
Stiffness Considerations HSR allows for proportionally less area of steel to resist the same strength demands as traditional reinforcement. This economy can result in a decrease in member stiffness, which should be considered. Most notably, this decrease is evident in minimum 2-way slab thickness limitations for which deflections need not be calculated; the minimum thickness limitation for 2-way slabs using Grade 80 reinforcement is approximately 10% and 20% larger than when using Grade 60 and Grade 40, respectively (Table 8.3.1.1). For lateral analysis, this consideration is not explicitly addressed by decreased modifiers for effective section stiffness in first-order linear analyses (Table 6.6.3.1.1(a)). However, some decreased stiffness has been shown in research studies. Engineers concerned with capturing this reduction more precisely could do so by using the alternative moment of inertia equations from Table 6.6.3.1.1(b).
• Engineers should continue to use fy of 60 ksi in their calculations for shear friction. Shear friction may begin to govern designs as the total area of longitudinal reinforcement is reduced with HSR. Correspondingly, greater attention should be paid to roughening construction practices if shear friction becomes critical in the design. • Larger crack widths correspond to HSR yielding. This may adversely affect certain serviceability criteria, such as steel corrosion. • From experience with HSR, it is the authors’ opinion that all HSR should be very clearly marked to distinguish it from typical reinforcement on a job site; a common solution is the use of spray paint. • Diagonal coupling beams, challenging to construct and typically heavily congested, could reduce diagonal reinforcement congestion through the use of HSR up to Grade 100. A secondary benefit is the production of a more favorable tie angle in the member, which will more efficiently use the diagonal reinforcement; this benefit is most pronounced with shallow diagonal coupling beams (Figure 1 ). In this example, the beam on the left achieves a more efficient tie
Important Considerations While there are many benefits to using HSR, there are times when the engineer should be cautious about specifying it. Below is a partial list of considerations that the authors believe engineers may face during design. 10 STRUCTURE magazine
Figure 1. Comparison of similar diagonal coupling beams with the same shear capacity.
angle to resist shear than the beam on the right, resulting in a reduction of bars to just 12 total in the Gr. 80 design. This is more substantial than reducing the Gr. 60 design by the ratio of stresses, 60ksi/80ksi, which would have produced 15 total bars. • Mechanical couplers are not permitted in plastic hinge zones utilizing HSR; the code commentary permits the EOR to override this if provided with adequate product data. • Caution should be exercised where the use of HSR indirectly reduces redundancy of reinforcement. An example would be chord or collector reinforcement taken from 2 bars (total) down to 1 bar, thereby reducing the redundancy of that element if there was a bar defect or splice failure. • Compression members utilizing HSR can attract and sustain higher demands. As a result, buckling becomes a critical consideration. Although columns typically come to mind in this application, ends of slender shear walls can also be of concern, especially those of asymmetric T- or L-type configurations. • In general, anchorage and force transfer should be of more concern now that higher bar stresses are being transferred. Anchorage or bond failures are more brittle and could preclude an intended ductile mechanism. An example of this would be inadequate tie development within nodal zones of strut and tie models. • The engineer should check with suppliers on the availability of HSR. Manufacturers may have size limitations on various bar configurations.
Conclusion For many years, using HSR in seismic applications has been restricted due to a lack of test data. However, a push from the structural engineering community has led to recent studies which alleviate the restriction on HSR in ACI 318-19. This article summarizes the research, changes in ACI 318, and various considerations that come with using HSR, mostly in seismic design applications. Changes in the ACI 318-19 include, among others, larger lap splice lengths for HSR, lower minimum longitudinal reinforcement limits, tighter transverse reinforcement spacing, and reduced stiffness of elements with HSR. The authors of this article would like to acknowledge and thank Noah Macias for editing this article.■ The online version of this article contains insights into research on the material specification of HSR and detailed references. Please visit www.STRUCTUREmag.org. Rahul Sharma is a Project Engineer with Hohbach-Lewin, Inc located in Palo Alto, CA. (rsharma@hohbach-lewin.com) Kion Nemati is an Engineer with Arup’s Structural Group in San Francisco, CA. (kion.nemati@arup.com) Jakub Valigura is a Design Engineer with KPFF Consulting Engineers in San Francisco, CA. (jakub.valigura@kpff.com) Nate Warner is an Engineer with Arup’s Structural Group in San Francisco, CA. (nate.warner@arup.com) Catherine Chen is an Engineer with Arup’s Structural Group in San Francisco, CA. (catherine.chen@arup.com)
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structural COMPONENTS
Beyond Bond Strength of Adhesive Anchors Testing, Design, and Specification By Alexis A. Clark, P.E.
A
variety of factors influence an engineer’s decision to use cast-in anchors or post-installed anchors including working principles, installation, and the impact on project timeline and budget. Above all, a licensed engineer shall hold paramount their code of ethics and the safety, health, and welfare of the public. At a time in which budget and scope have tightened for professional engineering work, it is difficult to allocate resources to sift through technical data and Figure 1. Quick references within an ICC-ES report. footnotes for a comprehensive comparison of post-installed anchoring systems. This article establishes an understanding of the Jurisdiction (AHJ). ICC-ES reports provide technical information chemical and physical factors that affect the performance of post- in a standard format but may vary significantly in depth and breadth installed adhesive anchor systems. It also explains how product testing between product reports. The Report sections include valuable inforis incorporated into design calculations and provides suggestions for mation for selecting the appropriate adhesive anchor system for an designing and specifying adhesive anchor systems. application (Figure 1). Why is this important? Inappropriate selection or improper instalICC-ES reports also include tables of published data that can be lation of adhesive anchor systems can result in a reduction in anchor used to design the anchor with ACI 318 anchoring-to-concrete capacity or anchorage failure. The consequences can lead to expensive provisions. Information in these tables can include the following: repairs, project delays, and, possibly, endangerment to public safety. • Specifications and physical properties of anchor elements The International Code Council Evaluation Service (ICC-ES) • Design information for anchor elements developed the Acceptance Criteria for Post-Installed Adhesive Anchors • Concrete breakout design information in Concrete Elements (AC308) in 2006. AC308 includes provi• Bond strength sions to qualify adhesive anchor systems for compliance with Load Reduction Factor Design (LRFD), per ACI 318-14, requires the International Building Code (IBC). Adhesive anchor systems the assessment of capacities corresponding to possible failure modes that demonstrate compliance with the IBC can be used with in tension and shear to determine which failure mode governs the the anchoring-to-concrete provisions of the American Concrete adhesive anchor system performance. An abbreviated method to Institute (ACI) publication Building Code Requirements for compare adhesive anchor systems is to compare nominal bond Structural Concrete (ACI 318). strengths as listed in ICC-ES report tables. These tables, however, Structural connection design includes cast-in anchors and post- may be differentiated by the condition of concrete, special inspecinstalled anchors. Cast-in anchors can be tion levels, in-service temperature range, used directly with ACI 318 anchoring-toor drilling method. Footnotes at the end of concrete provisions. Post-installed anchors tables can include several reduction factors are qualified per ICC-ES acceptance crifor design calculations. teria to (a) demonstrate compliance with The ICC-ES report concludes with the the IBC, and (b) obtain data to design manufacturer’s printed installation instructhe anchor with ACI 318 anchoring-totions (MPII), which should describe concrete provisions. congruent installation procedures to those In 2011, ACI developed the test stanthat have been tested and included in the dard Qualification of Post-Installed Adhesive body of the report. Anchors in Concrete (355.4) to qualify Adhesive anchor systems rely on adhesive adhesive anchor systems, thereby harmobonding as a result of a chemical reaction nizing AC308 with an ACI test standard. between hardener and resin. The bond To dive deeper, read Changes in Adhesive formed with the base material as a result Anchor System Approvals (STRUCTURE, of this chemical reaction can be affected by September 2015). several factors, including temperature and/ or the presence of dust or water. ACI 318 Section 17.8.2.1 notes characteristic bond Evaluation Service Reports stress parameters that should be included and Design Code in the language of an adhesive anchor specICC-ES reports serve as a third-party ification (Figure 2). This article focuses on evaluation of engineered products. These three bond stress parameters: drilling or evaluations can be used to demonstrate hole-cleaning methods, moisture condition product compliance with the IBC, sub- Figure 2. ACI 318-14 Section 18.8.2.1 encourages of the concrete, and temperature at time of ject to approval by the Authority Having specific parameters be specified. installation. 12 STRUCTURE magazine
comply with the MPII. In 2013, some manufacturers offered anchoring technology to help reduce the human error inherent to the holecleaning of adhesive anchor systems. Proper adhesive anchor installation These technologies include (a) a includes drilling into cured concrete torque-controlled anchor element using an approved drilling method, that relies on friction-hold rather cleaning the drilled hole to remove than adhesive bonding to transfer dust and debris, properly injecting load and thus requires no holethe adhesive, and inserting the anchor cleaning to achieve load capacity, element within the gel/working time and (b) a hollow drill bit system that of the adhesive (Figure 3). extracts dust while drilling. Figure 3. Installation steps and objectives. Properly cleaning the drilled hole can Due to rising numbers of severe have a significant impact on adhesive health conditions and fatalities anchor performance. AC308 proviassociated with silicosis, a lung dissions include reference and reliability ease attributed to inhalation of silica tests to establish a proper hole cleaning dust from concrete or masonry, the procedure. Reference tests establish a Occupational Safety and Health baseline cleaning procedure by which Administration (OSHA) heightened the adhesive is qualified and bond respirable silica dust regulations and stress values are established. Typical renewed enforcement in June 2017. steps for hole cleaning include blowOSHA’s Respirable Crystalline Silica ing out the drilled hole, brushing of Standard for Construction, known the hole with a steel wire brush, and as OSHA 1926.1153, or Table 1, blowing out the hole again. Although outlines the maximum levels and the blow-brush-blow method is a methods to reduce exposure to typical cleaning method for adhesive respirable silica dust allowable by anchor systems, the number of iteraapplication, including the cleaning tions for each step, proprietary steel method of post-installed anchor wire brushes, and prescribed pressure systems. of compressed air can vary for each Existing hole-cleaning technology system. In the subsequent reliability included in ICC-ES reports were test, the same anchor configuration is tested and confirmed to meet the tested at half the number of cleaning purpose of dust-removal to comply steps of the reference test with the with Table 1. Anchor manufacpurpose of validating that at least a turers that did not have existing certain percentage of the bond stress hole-cleaning technology partnered value is achieved under reduced holewith tool manufacturers to develop cleaning procedure. It follows then, dust-removal systems to comply with with the lowest possible reliability test Table 1. To date, some manufacturers cleaning procedure of 1 blow, 1 brush, Figure 4. Percent of bond stress to be achieved for various anchor categories. have included dust-removal systems 1 blow, the lowest allowable reference in an MPII without including them test cleaning procedure is 2 blow, 2 brush, 2 blow. in ICC-ES report testing. Some manufacturers that do include dustManufacturers have the freedom to select any level of cleaning procedure removal systems in an ICC-ES report may still require manual cleaning for reference tests. More cleaning iterations reduce the amount of dust steps, or their anchor may only be allowable in dry concrete conditions. and debris in the drilled hole, increasing bonding between the adhesive and concrete. Some manufacturers choose to use the minimum cleaning Effect of Moisture Conditions steps possible (2x2x2) with the intention of reducing the expectation of installer diligence to follow manual cleaning procedures, relying on the Adhesive product testing per AC308/ACI 355.4 establishes a strength adhesive anchor system’s resilience to deliver performance. reduction factor (φ-factor) relevant to the reliability or sensitivity of If an adhesive anchor system does not achieve a specific percentage of the product with respect to installation conditions. Adhesive sensitivity the reference test bond stress value in reliability testing, the anchor may can be influenced by mixing the hardener and resin, hole cleaning, report a lower category than intended or the number of iterations or and moisture content of the base material, among others. φ-factors intricacy of cleaning steps may increase in the reference test to provide vary for tension loads, as shown in Figure 5. Note that adhesives a cleaner hole in which the adhesive can reliably reach the intended with high reliability have a φ-factor of 0.65 while adhesives with low level of performance (Figure 4). Intricate cleaning steps to help achieve reliability have a φ-factor of 0.45. φ-factors for an adhesive product and maintain bond stress include proprietary steel wire brushes specific can vary with respect to anchor diameter, special inspection levels, to the adhesive anchor system, or drill-mounting of brushes that may core-drilling, or whether the drilled hole in the concrete is dry, waterhave wider or more densely packed bristles to remove dust. saturated, water-filled, or wholly submerged. In 2011, Concrete International published A Field Study of Adhesive Lower φ-factors typically result from a single adverse installation conAnchor Installations, reporting that 77% of installations did not dition or compounding adverse conditions. Some adhesive products
Reliability Testing of Manufacturer’s Installation Procedure
APRIL 2020
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perform at the highest level of reliability, achieving a 0.65 φ-factor for both favorable and adverse conditions, like dry concrete and water-saturated concrete, respectively. It is essential to be aware of any compounding conditions in testing for reliability as the resulting φ-factor directly affects design capacity and performance of the anchor. Other adhesive products have a φ-factor of 0.65 for a 3⁄8-inch-diameter anchor element and a φ-factor of 0.45 for a ½-inch-diameter anchor element. Some φ-factors are obtained with the requirement that all adhesive anchors, regardless of installation orientation, are under continuous inspection, although 2015 IBC Chapter 17 requires continuous inspection for only adhesive anchors that are horizontal-toupwardly-inclined with sustained tension loads. φ-factors are strongly influenced by the presence Figure 5. The reliability of an adhesive anchor is of water that may affect the bond of an adhesive reflected in a φ-factor. anchor system to the base material. Although the office environment in which we design anchorage is climate-controlled and dry, the job sites where the product is installed rarely are. AC308 defines dry concrete as concrete that has not been exposed to water in 14 days. Most regions of North America are likely to experience precipitation, regardless of season, within a two-week period. ACI requires consideration of moisture conditions in the design phase. Whether an anchorage design is generated in response to a Request for Information (RFI) for installation later that Figure 6. Published cure times required at approximately 41°F. day or a general notes section is developed for anchors that are installed throughout the duration of a project, watersaturated concrete is realistic to assume for a design basis.
a given base material temperature before loading is critical to the performance of the adhesive bond. A general rule-of-thumb followed by many installers is to wait 24 hours after installing an adhesive anchor system before loading, regardless of the MPII. Some products require cure times that exceed this rule-of-thumb, as shown in Figure 6. Additional cure time may be required in water-saturated conditions, as shown in footnotes in either an ICC-ES report or MPII. Gel/working time is another significant consideration in adhesive anchor selection. During gel/working time, the installer must inject the required amount of adhesive into the drilled hole with no air voids, insert the anchor element to the required embedment depth, and position it properly. At elevated temperatures, most products have a gel/working time of at least five minutes in which the installer can reasonably execute these steps; other products allow for only 90 seconds of gel/working time. Depending on their chemical makeup, products may require special conditioning to be used in certain environmental conditions. Water-based adhesives require minimum conditioning of the adhesive product to above 32°F, and a common conditioning requirement among products is a minimum of 41°F. Other products require installers to condition adhesive products to 70°F when base material temperatures are less than 70°F.
Basis-of-Design Parameters in ACI 318
Impacts of Installation Temperature Adhesive anchors cure because of a chemical reaction between a precise ratio of hardener and resin. Temperature greatly influences the rate at which the adhesive cures. When the concrete temperature is high at the time of installation, the reaction is accelerated; when the concrete temperature is low at the time of installation, the reaction slows. Four considerations of temperature include the range in which the product can be installed, the required cure time at a given temperature, the gel/working time at a given temperature, and conditioning requirements of the product to be installed properly in a given application. Installation temperatures are included in ACI 318 anchoring-toconcrete provisions. Adhesive anchor manufacturers typically test their products for a wide range of installation temperatures. The most common temperature ranges include 41°F to 104°F. Some, although not all, products have been tested for installation at minimum temperatures as low as 14°F. Reference the ICC-ES report for the installation temperatures specific to an adhesive anchor system to validate applicability in the realistic temperatures your projects may experience. Ideally, adhesive anchor systems strike a realistic balance between cure time and gel/working time. As construction schedules continue to tighten, priority is given to shorter cure times that allow for more immediate loading. Waiting for the full required cure time for 14 STRUCTURE magazine
ACI 318 recognizes the reliability of adhesive anchor system performance is influenced by adverse job site conditions including moisture condition, temperature at time of installation, hole drilling methods, and cleaning procedures. While these aspects are addressed by testing per AC308, the resulting bond strengths, reduction factors, and conditions of use included in the ICC-ES report vary significantly between products. A best practice to help ensure the adhesive anchor system meets ACI 318-14 Section 17.8.2.1 requirements is the inclusion of basis-ofdesign parameters in your design and specified in the general notes. Examples include: • Cracked concrete • Water-saturated concrete • Base material temperature at the time of installation of 23°F to 104°F • Allowable drilling methods to include hammer-drill, hollow drill bit, and diamond core drill By including basis-of-design expectations of the final installed product, engineers can help ensure reliable performance in realistic job site conditions.■ The online version of this article contains references. Please visit www.STRUCTUREmag.org. Alexis A. Clark is the Structural Engineering Trade Manager for Hilti North America. (alexis.clark@hilti.com)
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structural PRACTICES
Federal Changes for Post-Installed Adhesive Anchors By T. J. Bland, P.E.
T
he wheels of change turn slowly when it comes to government regulations. For federal highway infrastructure, some of the regulations for new construction have not been modified for decades, but developments in the past two years regarding
the adhesive anchor industry are nothing short of a sea change. The most significant development was the issuance of a new technical advisory for bridges and structures by the Federal Highway Administration in January of 2018 (T5140.34). It establishes new guidelines for the installation and inspection of adhesives used in new and existing federal-aid projects. An additional development involves ongoing efforts by the federal government to strengthen the standards used under the Buy American Act. This article explains the recent history of state-by-state regulations in the industry, the review and adoption progress for the new regulations, and the significant impact of the developments on the formulation, specification, and use of anchoring adhesives. The new technical advisory is the third advisory issued since the investigation into the 2006 ceiling panel collapse in the I-90 Seaport Connector Tunnel in Boston. The new advisory states that “since the original technical advisory was issued, two National Cooperative Highway Research Program (NCHRP) studies have been completed, and the industry and the American Concrete Institute (ACI) have made significant advancements on regulating adhesive anchor systems and installation.” Industry efforts over the past 10 years have led to the new advisory, and it makes several recommendations.
Focus and Key Provisions T5140.34 focuses primarily on structural connections that are under load. For new Federal-aid projects where post-installed adhesive anchors are deemed a necessity, they should be designed using the American Concrete Institute’s ACI 318-14, Building Code Requirements for Structural Concrete, or later editions for the given loading condition (vertical, horizontal, or overhead) and use only adhesive anchor systems qualified per ACI 355.4-11, Qualification of Post-Installed Adhesive Anchors in Concrete, or later editions for the same loading condition. For existing projects, where applications of post-installed adhesive anchors are under permanent sustained tension and where the adhesive anchor system was not specifically qualified for use under that loading per ACI 355.4-11 or later editions, the owner should either: 1) Institute a rigorous and regular inspection program that considers importance and redundancy to maintain an appropriate level of confidence in the long-term performance of these existing adhesive anchors. This may require developing a testing protocol and program to determine the site-specific ultimate capacities and creep characteristics of the adhesive over the expected life of the structure. Or, 2) Retrofit and/or replace the existing adhesive anchors with a post-installed mechanical anchor or post-installed adhesive anchor meeting the requirements of ACI 318-14/ACI 355.411 or later editions. The rationale behind the decision can be found in the technical advisory, and the specific details can be found in the code itself. One of many key takeaways is that this technical advisory brings a federal 16 STRUCTURE magazine
requirement of a national standard, for the first time, to the use of post-installed adhesive anchors in roadways and structures – and it requires that each state abides by these standards. In short, adhesive anchors used in federally funded infrastructure projects must be approved to the same standards as adhesives specified in accordance with the International Building Code (IBC). Some of the critical provisions of ACI 318-14 and ACI 355.4-11 that engineers and specifiers should be aware of include: • The ACI and Concrete Reinforcing Steel Institute (CRSI) have established an Adhesive Anchor Installer certification program. The purpose of the program is to ensure uniformity in the knowledge base of those that install anchors on the parameters that may affect anchor performance, including hole drilling, hole cleaning, adhesive storage, adhesive mixing, and the importance of Manufacturer’s Printed Installation Instructions (MPII). • Installation of adhesive anchors horizontally or upwardly inclined (including vertically overhead) to support sustained tension loads shall be performed by personnel certified by an applicable certification program, such as the American Concrete Institute (ACI)/Concrete Reinforcing Steel Institute(CRSI) Adhesive Anchor Installer Certification program, or equivalent. • ACI 318-14 requires continuous inspection of adhesive anchors installed in horizontal or upwardly inclined orientations to resist sustained tension loads, but it is left up to the owner to establish the inspector qualifications. • ACI 318-14 establishes evaluation requirements under various adverse loading conditions, including sustained tension.
State Adoption Historically, individual states have maintained their own approval regulations for adhesive anchoring materials used on infrastructure projects. They kept their own authorized materials lists or approved products list, and the standards varied from state to state. When T5140.34 was published in January 2018, only one state, Wisconsin, was requiring products tested following the building code
consistent with law, encourage recipients of new Federal financial assistance awards pursuant to a covered program to use, to the greatest extent practicable, iron and aluminum as well as steel, cement, and other manufactured products produced in the United States in every contract, subcontract, purchase order or sub award that is chargeable against such Federal financial assistance award.” The original 1954 Buy American Act considered a product “foreign” if the cost of the foreign products used in the materials constituted 50 percent or more of the total cost. In the most recent executive order published in July of 2019, it lowers the threshold for steel to 5 percent or more. For all other end products, it lowers the cost to 45 percent or more. For products made in the adhesives industry, the majority of the cost must be paid in the United States, or the related projects will not qualify for federal money.
Moving Forward For engineers and specifiers, the most conservative route is to specify adhesive anchors that are manufactured domestically and meet the new federal requirement. Even though a majority of states have not yet strictly adhered to the new regulations, it is only a matter of time before there is widespread compliance. In conclusion, the new developments discussed in this article reinforce the importance of products that are both code-compliant and made in the USA.■ T. J. Bland is the President of Adhesives Technology Corp. in Pompano Beach, Florida. (tjbland@atcepoxy.com)
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requirements. Adoption by other states has been limited, but this is not surprising, particularly if you understand the history within the industry. The adoption of the new requirements varies from state to state and has been constrained by several factors. First, some road and bridge officials may not be aware of the new standards – trends in adhesive anchoring are not exactly front-page news. Second, the amount of applicable federal work varies significantly from state to state. Large states, like Texas, have always had a robust system in place to monitor, approve, renew, and test products. Road construction is big business in Texas, so it is no surprise that it has already adopted specific classes of products that align with T5140.34. Third, some states want to be sure that their published requirements are compliant with T5140.34 while also meeting other construction requirements that are unique to their state. For example, Florida has its own anchoring testing because aggregate in the state is typically softer than in other parts of the country. For this reason, Florida developed its own creep test for anchoring. If a product is to be certified in Florida, it will need to meet state and federal standards (once they are officially adopted). While state-specific requirements might be delaying overall adoption, it is a positive thing when such requirements go above and beyond the federal requirements. Since January 2018, the following states have adopted the new requirements: Arizona, Iowa, Louisiana, Massachusetts, Michigan, Minnesota, New York, Oregon, Texas, and Wisconsin. It is important to note that the remaining states are not sitting on their hands but are most likely in some stage of adopting the new standards. California, for example, announced in January 2020 that it will be sunsetting its legacy requirements on April 20, 2020, in favor of entirely new acceptance criteria, the first to require not only code approved products but also only those products that meet a specific minimum performance threshold. States that often follow California’s lead will surely be next in line. Smaller states, which do less federal road and bridge work, have been slower to adopt. In some instances, it is a question of staffing and prioritization. In other cases, smaller states follow the lead of neighboring states, which also may have not yet acted on the new requirements. Another factor that should not be overlooked is the impact of T5140.34 on existing projects, which have both retrofit and inspection requirements. The ongoing cost associated with this type of inspection or retrofit should drive the specification for codeapproved products by the engineers working at state Departments of Transportation (DOT) levels even before the state mandate for such products is drafted/ratified. Currently, engineers may already be specifying products that meet the intent of the federal regulations without being “told to do so” by their current state requirements. This may be another reason why adoption has been slow.
The Buy American Act The next significant development is the ongoing effort by the federal government to enforce and expand the Buy American Act, initially proposed by President Eisenhower in 1954. The White House issued two executive orders in 2019 on this topic, both to enforce the Buy American Act “to the greatest extent permitted by law.” In January of 2019, the executive order directed government agencies and departments to encourage recipients of federal project dollars to use products, of almost all kinds, that are produced in the United States. It stated, among other points: “Within 90 days of the date of this order, the head of each executive department and agency administering a covered program shall, as appropriate and to the extent
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structural REHABILITATION Adaptive Reuse of the Apex Hosiery Company Building Part 3: Adaptive Reuse Feasibility Analysis By D. Matthew Stuart, P.E., S.E., P.Eng, F.ASCE, F.SEI, A.NAFE, SECB
T
his four-part series (Part 1, STRUCTURE, November 2019, Part 2, January 2020) discusses how the collapse of a
building during a demolition operation in Philadelphia in 2013, which resulted in several fatalities, led to the enactment of a City Ordinance to prevent similar calamities. As a result of the Ordinance, the author became involved with the structural investigation, review of the Site Safety Demolition Plan, and Demolition Special Inspections associated with the adaptive reuse of the Apex Hosiery Company Building located in Philadelphia.
South Side of Building The typical two-way slab analyzed as a part of the investigation and feasibility study of the south side of the building involved the remaining east-west three-span structure and a typical north-south spanning slab of no more than five equal spans. Both slabs were analyzed using the Portland Cement Association (PCA) spSlab software. This software utilizes the Equivalent Frame Method (EFM) of analysis recognized by ACI. The EFM involves the representation of the three-dimensional slab system as a series of two-dimensional frames that are analyzed for the loads acting in the plane of the same frames.
Figure 14. Lateral capacity of the post-renovation three-story building was assumed adequate based on the theory that the original six-story building sail area and mass translated to larger wind and seismic loads.
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Figure 13. Analysis of demolition equipment and debris loading conditions revealed that proposed demolition equipment could be safely operated, but temporary storage of concrete debris was limited.
The analysis was based on the conventional bottom and top reinforcing bar diameters and spacings documented as a part of the field assessment and yield strength of 40 ksi based on the laboratory test of two samples obtained from a slab that was scheduled to be demolished. Typically, the results of an analysis to determine the load-carrying capacity of an existing vintage reinforced concrete structure are greater than that which was specified by the original designer. This is because the ultimate strength method used for current day design and analysis typically provides greater capacities than that which would have been obtained via the working stress method of concrete design used in the 1920s. However, using current-day methods of analysis, a superimposed service load capacity of only 120 psf was determined. This relatively low calculated capacity probably resulted because the method of analyzing two-way flat slabs in the early 20th Century was based on concepts that did not accurately represent the true behavior of this type of structure. Never the less, this capacity is consistent with the 1929 Philadelphia Building Code for light manufacturing buildings, as documented in the 18th Edition of Kidder Parker Builders’ Handbook. As a result, it was concluded that the Apex Hosiery Company’s utilization of the building did not involve heavy manufacturing that required a live load capacity of 200 psf per the same 1929 code. The 120-psf uniform load capacity was input into the spSlab software as a 20-psf superimposed dead load and a 100-psf live load. This was based on the combined superimposed dead load of 15 psf for partitions (as required by the IBC) and 5 psf for miscellaneous suspended mechanical equipment. A superimposed dead load for ceilings was not included because there were no ceilings shown on the architect’s renovation drawings. The 100-psf live load was based on the IBC minimum requirement for residential public rooms and corridors, and the first-floor retail spaces located above the south side basement. The minimum IBC live load for the residential spaces on all floors of the building is only 40 psf. A review of the structural drawings issued for the renovation project indicated that floor live loads used for the design were 40 psf, 100 psf,
and 80 psf for Dwelling Units, Lobbies and Stairs, and Corridors, respect- System, which was based on the early to mid-20th Century Working fully. Also, 15 psf was included as a partition allowance. All of these same Stress method documented in the Taylor, Thompson, and Smulski design loads were less than or equal to the calculated 120-psf capacity of textbook on Plain and Reinforced Concrete, Volume 1. The existing floor the existing two-way slab. Therefore, it was determined that the adaptive slab was analyzed as a 6-inch structural slab supporting a 1-inch-thick reuse of the existing remaining south side structure was feasible. non-composite concrete topping. The flexural moment capacities for The investigation of the demolition equipment and debris loading Unit B, in other words, the diagonal positive moment span, and Unit conditions for the south side slab indicated that the existing distribution C, the negative moment at the column support, were established as a of top and bottom reinforcing in the east-west direction did not match part of the analysis. The results of the analysis indicated that the slab the moment demand requirements of the spSlab software output. As a system was capable of supporting a 120-psf superimposed uniform result, it was necessary to redistribute the negative moment provided load similar to that established at the framed two-way slab at the by the software analysis to the positive moment region to justify the south side of the building. worst-case demolition equipment and debris loading conditions. The The results were based on the concept that the diagonal slab simplemaximum negative to positive moment redistribution was limited to spanned a distance of 3⁄5 of the clear span between the existing column 20%, as allowed by Section 8.4 of ACI 318. As a result of the analysis, it was determined that the proposed mechanized equipment could be safely operated inside the building during the demolition operation. However, the triangular volume of demolished concrete debris that could be temporarily stored in the span immediately adjacent to the span in which the equipment would be operating was determined to only include a maximum height of 3 feet and maximum width of 5 feet in the eastwest direction in a continuous north-south mound, based on a unit debris weight of 120 pcf, as illustrated in Figure 13. A lateral load analysis of the remaining existing building was not included as part of the assessment for the following Use for all types of concrete and grout applications, from slabs-on-grade to reasons. The reduction in the height and containment tanks, multi-story post-tension structures to bridge decks. footprint of the remaining building from its original configuration significantly reduced the sail area of the exterior vertiADVANTAGES cal surfaces of the building. As a result, the lateral wind loads on the remaining ¡ Maximize joint spacing (up to 300 ft, L/W 3:1) ¡ Enhance compressive and flexural strengths building would be reduced considerably ¡ Prevent shrinkage cracking and curling ¡ Eliminate pour/delay strips from that which it was assumed to have ¡ Thinner slabs and walls viable ¡ Reduce long-term relaxation of P/T tendons been initially designed for. and shear wall stresses Therefore, because the lateral resisting ¡ Reduce reinforcement requirements capacity of the remaining three-story ¡ Minimize creep and moment ¡ Improve durability and lower permeability building seen in Figure 14 was more than ¡ Minimize waterstops likely designed for a greater accumulated ¡ Increase abrasion resistance 30-40% wind load of the original six stories, it was reasonable to assume that the lateral load resisting capacity of the remaining structure was adequate. Also, although it is unlikely that the original designer of the structure analyzed the building for lateral earthquake loads, for this investigation, it was assumed that, similar to the wind loads, the current Code-based seismic base shear for the remaining three-story building was significantly less than the potential seismic loads on the original six-story building.
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North Side of Building The existing slab at the north side of the building was analyzed using the vintage method previously described for the SMI
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Figure 16. Feasibility analysis was based on top and bottom concentric reinforcing hoops with a 27 ksi yield strength resulting from a laboratory test of this sample.
Figure 15. Analysis indicated that the north-side slab system could support a 120 psf superimposed uniform load similar to that established at the framed two-way slab on the building’s south side.
Figure 17. Interruption of SMI slab reinforcing hoops at new stair and elevator openings showing required additional slab supports.
capitals, and the slab, drop panel, and column capital cantilevered from the face of the column to support the end reaction of the Unit B diagonal span. The analysis was based on the bottom and top concentric reinforcing hoops documented as a part of the field assessment shown in Figure 15 and a yield strength of 27 ksi based on the laboratory test of one hoop sample shown in Figure 16 obtained from a slab that was scheduled to be demolished. An analysis of the SMI slab was also conducted for the same demolition equipment and debris loading conditions used for the south slab. The results of the analysis indicated that the northern SMI slab was capable of supporting the same demolition operations as the south slab. As previously described, the SMI method of calculating positive moments is based on a simple span rather than continuous span condition, and negative moment is based on a cantilever condition around the circumference of the columns for the support of the surrounding reactions from the simple span slabs. This method of analysis was conducive to the proposed renovations because the interruption of the continuity of the existing slab as a result of the north-south line of demolition along the east face of the existing drop panels did not adversely impact the structural integrity of the remaining interior slab span that was converted to an end span condition. However, because it was determined that a small portion of the top hoop reinforcing extended beyond the edge of the drop panel, it was necessary to extend the originally proposed line of demolition slightly further east, beyond the east edge of the drop panel, to avoid damaging the outer most top bar hoops. Adjusting the extent of the demolition was required because the flexural capacity of the existing SMI slab system is based on continuous, uninterrupted concentric rings of reinforcing bars, as required to resist the hoop stresses imposed by the deformation of the concrete slab. Therefore, all of the top hoops 20 STRUCTURE magazine
in the Unit C group had to be protected from damage or disruption of the surrounding concrete encasement. A similar requirement to extend the east side of the line of demolition was also needed for the outer most hoops of the bottom bars located in the north-south span of the Unit A portion of the slab located along the line demolition. However, it was determined that the location of these same bottom hoops did not extend any further east than that documented for the top hoops over the drop panels. For reasons similar to that described along the eastern edge of the demolition, interruption of the SMI slab reinforcing hoops at large openings associated with new stairs and elevators required additional slab supports beyond the new supplemental steel framing at the perimeter of the stair opening. This was also true for the new loadbearing CMU walls at the perimeter of the elevator opening shown on the renovation structural drawings. The approximate extent and location of the additional slab supports that were required at a typical large opening in the SMI slab was provided on a plan shown in Figure 17.
Conclusion The results of the feasibility study for both the conventionally reinforced and SMI two-way slabs indicated the existing remaining structure was adequate for the proposed adaptive reuse with only a few minor modifications required at the edge of demolition and supports at new openings for the SMI slab. Part 4 of the series will include a discussion of the Demolition Special Inspections and the post-demolition assessment of the remaining structure.â– Matthew Stuart is the Senior Structural Engineer at Pennoni Associates Inc. in Philadelphia, PA. (mstuart@pennoni.com)
Preserving the Many Glacier Hotel By Ian Glaser, P.E., and Christine Britton, P.E.
The Many Glacier Hotel after the completion of the renovation in 2017. Courtesy of Mark Bryant Photographics.
T
he Great Northern Railway built the Many Glacier Hotel from basement features exterior balconies on all sides and all levels, grand 1914 to 1917. This iconic hotel, built in the style of a Swiss masonry chimneys in the public spaces, a four-story lobby atrium chalet, is perched on the edge of Swiftcurrent Lake overlooking the space framed with log columns and trusses, and an expansive dining glaciated valleys and mountains of Glacier National Park’s less-traveled room with a timber and steel-rod trussed roof. The structural rehaeast side. The Many Glacier Hotel was listed on the National Register bilitation scope involved repairing deteriorated framing, fortifying of Historic Places in 1976 and was designated as a National Historic the roof framing for the 135 psf roof snow load, and retrofitting the Landmark in 1987. However, due to significant deficiencies in the building’s lateral system for Seismic Design Category C. The buildknob-and-tube wiring, the plumbing and fire-suppression systems, and ing’s original lateral force-resisting system consisted merely of interior the gravity and lateral load-resisting structural systems, the structure stud walls surfaced with Sacket Board (a more brittle precursor to was placed on the National Trust for Historic Preservation’s annual gypsum wallboard) and exterior walls surfaced with board sheathing. list of “America’s 11 Most Endangered Historic Places” in 1996. Because the lateral force-resisting system upgrade was voluntary, 75% The National Park Service initiated a comprehensive, phased rehabili- of current-day code-prescribed seismic forces were used as permitted tation around 2000. The first phases focused on the most immediate by the International Existing Building Code. All upgraded and new needs of the building’s exterior. In structural systems had to be con2004, JVA, Inc. was engaged as cealed within the building’s walls, the structural engineer in partnerfloors, and chimneys to maintain ship with the architect, Anderson the visitor experience. Hallas Architects, P.C. The team The roof framing over the dining worked on the rehabilitation for room had been concealed by a 13 years until its completion in dropped ceiling installed in the 2017. Swank Enterprises was the 1930s. After selective strengthengeneral contractor for all the coning of the purlins using lumber struction phases, which totaled that matched the original lumber approximately $42 million. in appearance, the dropped ceiling The hotel is situated in an alpine was removed. The timber and steelenvironment, and the structural rod trusses were re-exposed, paying systems were suffering due to homage to the railroad engineers extreme environmental condithat designed and built them. The Many Glacier Hotel in April 1956. Snow has reached the second floor of tions. In winter months, drifted the lobby. Chimney at left was removed at an unknown date before the recent In the guest wings, the partitions snow can reach the third floor of rehabilitation work. Courtesy of Glacier National Park Archives. between rooms did not align across the hotel, 20 feet above grade on the central corridors and did not the uphill side, with a design ground snow load of 180 pounds per stack perfectly from floor to floor. The partitions on one side of the square foot. The annual onslaught of snowmelt running under the hallway were mobilized as shear walls so that utilities could be routed building was undermining the foundations and causing the wood on the opposite side. The partitions were reconstructed as shear walls to framing at the base of the building to deteriorate. resist wind and seismic loads in the guest wings’ short direction using The approximately 140,000-square-foot hotel is framed with a mix their average centerline along the building height. Having a height-toof heavy timber, log, and dimension lumber. The foundations and length aspect ratio of approximately 5:1, the lower stories are concrete chimneys are stone masonry. The four-story building with a walkout and the upper stories are wood. Steel rod holdowns extend continuously 22 STRUCTURE magazine
Interior of the dining room featuring the chimney and the original roof trusses. Courtesy of Mark Bryant Photographics.
Braced frame in the basement level of the lobby. Courtesy of Mark Bryant Photographics.
from the top of concrete to the attic level, and collectors were installed by re-siding. Below grade, the unreinforced masonry foundation was at each diaphragm level. The shear walls were re-clad with their historic replaced with a reinforced concrete grade beam over micropiles. The board-and-batten wainscoting. Each shear wall was founded on a new reinforced chimney became a shear wall in its long-axis direction. concrete grade beam supported by new micropiles capable of resisting The lobby wing features a ring of twenty 30-inch-diameter Douglasuplift forces over 100 kips. A small rig was driven inside the building Fir columns that extend from the basement to the roof and form the to install piles to an approximate depth of 50 feet into the bedrock. grand atrium space. The main level had very few walls that could be To reduce seismic mass, four utilitarian chimneys that were concealed used as lateral force-resisting elements. Steel moment frames were ruled behind finishes and that historically expelled gases from wood-burning out since they would impact the aesthetic of the space. Instead, the stoves in the guest rooms were removed. One other chimney was log columns were mobilized as vertical collectors that receive upperremoved at an unknown date before the rehabilitation. Five stone level shear forces and transfer them into the strengthened first-floor masonry chimneys remain: three feature fireplaces for hotel visitors diaphragm and, in turn, into braced frames in the basement. The in the dining room, lobby, and lounge areas, one serving deluxe guest braced frames in the lobby’s basement are some of the only structural rooms at each level, and one serving the kitchen. retrofitting measures that are visible to the public. The existing chimneys all required reinforcement and positive attachEarly during the lobby-wing construction phase and once finishes ment to the building’s diaphragms. Each chimney was unique and were removed, the log columns were discovered to be spliced at the required a different structural solution. Chimney reconstruction was first-floor level and not continuous from the basement to the roof not a viable option because of the desire to preserve the historic fabric as the original drawings had indicated. Bending moments across the and to control costs. Some chimneys were used as shear-resisting ele- splices are resolved with a matrix of 1-inch-diameter, 3-foot-long lag ments with new collectors; others were tied into the diaphragms and bolts installed at steep angles across the splices via a custom-made jig. their mass was resisted by nearby shear walls. Four of the log column bases were also discovered during construcThe dining room chimney has two flues. The flue that originally tion to be deteriorated, and their beehive-shaped cones of internal served the boiler in the basement was cleaned, reinforced, and grouted. deterioration were profiled using a resistance drill. Deterioration The chimney’s shoulder on the opposing side was removed, a rein- extended as high as 3 feet above the basement floor. At these four forced concrete chord installed, and the shoulder was refaced with locations, the framing above was shored, the deteriorated log column the original stones in their original positions. The dining room flue, bottoms were carefully extracted, and the deteriorated material which follows the reinforced shoulder, remains operational. was removed from the bottoms leaving only the intact outside The lobby chimney weighs almost 500 shells. The remaining undamaged seckips. Its basement-level flue was intertions of the log columns were reset on nally reinforced and grouted from top to steel standoffs and then clad with the bottom. The outer leaf of stone was pinned original, hollowed-out shells. to the reinforced core. The lobby-level flue Through innovative structural solutions remains operational. The lounge chimney that preserved the historic fabric of the has only one flue and it also needed to stay building, the Many Glacier Hotel now operational. A 40-foot-tall, 20-inch-diamcomplies with current building codes, eter, 16-gage steel round form was lowered and visitors can experience the into the 24-inch square flue via a crane. structure’s original charm and The spaces between the original square flue grandeur for years to come.■ and the new steel form were reinforced and grouted. The chimney serving guest rooms Ian Glaser is JVA, Inc.’s Director of Historic on each floor, having 8 flues, is situated at Preservation. (iglaser@jvajva.com) the end of a guest wing. The exterior stud Christine Britton is a Project Engineer in wall concealed its back face. The stud wall the Historic Preservation group at JVA, Inc. was removed, the stone face reinforced and Reinforcing cage inserted into the full-height flue of the dining (cbritton@jvajva.com) surfaced with shotcrete, and then concealed room chimney. Courtesy of Dan Cooke, JVA, Inc. APRIL 2020
23
construction ISSUES Building Above Underground Coal Mines By Gennaro G. Marino, Ph.D., P.E., D.GE, and Abdolreza Osouli, Ph.D., P.E.
W
hen underground coal mining began in the 1700s in the U.S., many of the mines were located far away from developing
city infrastructure. There was little thought of potential expansion over these mined-out areas or the effects of long-term subsidence. Until the 1970s, most mine design was essentially done by rule of thumb and focused on short-term operational needs. As cities began to expand into mined-out areas, city infrastructure became exposed to the risk of damage caused by mine subsidence. There are presently 17 states which have active and abandoned underground coal mines that require significant expenditures each year to address mine subsidence risk and damage.
Geologic Setting In the U.S., coal beds lay relatively flat and are found in the bedrock between layers of mainly sandstone, shale, and limestone. In some regions of the U.S., there are multiple coal seams that have been mined. A coal seam is considered mineable by underground methods when it is at least 30 inches thick. Because of the number of mineable seams in West Virginia and Pennsylvania, these states contain the most areas with multiple coal workings.
Mining Methods The underground mining of coal has evolved. Most older abandoned mines were developed using room-and-pillar methods. This method involved extracting the coal first by manual excavation and later by mechanical means. After coal extraction, this method left voided areas that contained unextracted coal (i.e. pillars) to support the mine roof and overburden. Over time, these pillars were more systematically placed. Figure 1 provides an illustration of room (void) and pillar (coal) workings. Although the pillars in the illustrations are prismatic in shape, they can be quite irregular and virtually any shape, especially in older mines. The amount of coal extracted with this method typically ranges from 60% to 75% by area. A common high extraction method of coal mining used today is called longwall mining. This is a mechanized system of mining where 100% of the coal seam can be removed in up to typically 1,500-feetwide by mile-long strips.
Mine Stability The stability of the underlying room and pillar mine is directly related to the risk for future subsidence and the nature of the subsidence in the ground above. Consequently, the accuracy of these assessments plays a key role in determining proper land development decisions, such as how to avoid expensive subsidence 24 STRUCTURE magazine
Figure 1. Illustration of room-and-pillar coal workings.
mitigation or improper solutions, which can result in severe losses due to subsequent subsidence. In assessing the risk of surface subsidence from an underlying coal mine, there are three basic modes of failure of the mine structure that should be evaluated. • Mine-roof collapse into a mine opening, • crushing of multiple mine pillars, and • punching of multiple mine pillars into the mine floor. Surface subsidence from the collapse of the mine roof occurs when upward caving in one of the mine rooms or room intersections breaches the bedrock surface. This phenomenon is also called chimney subsidence. The upward caving potential depends on the rock overburden conditions and the bulking or volume expansion of the caved material. The upward caving can be obstructed if a competent zone of rock in the overburden were able to bridge across the collapsed roof. Where no sufficiently competent rock zone exists, chimney subsidence will continue upwards until it breaches the bedrock surface, unless it chokes off. The second mode of failure that results in surface subsidence is the yielding of the mine pillars or “pillar crushing.” This mode depends on the demand and capacity of the pillar. The third mode of mine failure that can induce land subsidence is a mine-floor bearing failure. This phenomenon has also been termed “pillar punching” and “floor squeeze.” As with pillar crushing, several pillars must fail for significant subsidence to be realized on the ground surface. The potential for subsidence from a mine-floor failure depends on the loading on the pillar and the strength and durability of the floor materials. Pillar punching typically results when the mine floor is exposed to groundwater, dramatically reducing the overall floor bearing capacity. Another component that can compromise the floor strength is the presence of fissures in the rock.
Mine Subsidence Movements Mine subsidence expresses itself on the ground surface in the form of pits (sinkholes) and sags or troughs. Pit subsidence exclusively occurs
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from chimney subsidence. This surface expression can range in size from a pothole to typically 30 feet in diameter and over 10 feet deep (Figure 2). These pits can extend to elongated-shaped sinkholes under very severe conditions. Sag or trough subsidence expresses itself on the ground surface like a bowl- or swale-shaped depression. For room-and-pillar and high extraction mines, these expressions can range from one hundred to thousands of feet across with depths from 1 to 7 feet. The specific character of the sag or trough depends on the site conditions, most importantly: • Mode of a mine failure • Mine depth • Mine layout • Mining method • Extraction height • Soil and rock overburden • Surface topography Smaller sags occur at shallower mine depths and result from room roof collapse where the soil cover slumps into the breach in the bedrock. These events are usually circumscribed by faulted tension cracks on the ground surface. Although these sags are of smaller diameter, they can be quite deep at greater extraction heights and/or shallow mine depths or soil cover. Sags or troughs in the range of more than 300 feet to 800 feet across occur above room and pillar mines, are generally 1 to almost 4 feet deep, and are the result of multiple pillar deflections. Larger subsidence events are caused by longwall mining. However, most of the movement from these events occur during mining, so there is some ability to implement mitigation measures where possible. These very long subsidence troughs occur sequentially and parallel to each other, with overlapping movements. Individual troughs are typically 4 to 6 feet deep and several thousands of feet across. In addition to vertical surface deformations, sag/trough events induce differential horizontal displacements which result in centralized compressive zones and circumferential tension zones. In relatively flat terrain, the maximum horizontal displacement for the larger subsidence events typically occurs in the direction of the bottom of the subsidence basin and is generally in the range of 10 to 30 percent of the maximum vertical movement. In rugged terrain, the horizontal displacements can be significantly more exacerbated and generally follow the direction of the steeper topography.
Subsidence-Structure Interaction Given the risk of mine subsidence, the most important aspect of mine subsidence engineering is the estimation of structural response and associated damage. The general behavior of a surface structure to pit mine subsidence depends mainly on the nature of the structure and the subsidence characteristics. Pit subsidence under or in the vicinity of a building, if initially small or of pothole size, may result in no or slight damage. However, such an event would indicate that this area of ground is unstable and should be treated as a hazard because the pit can unpredictably expand at any given time until it is treated. Larger pits or sinkholes that develop under buildings typically result in concentrated heavy damage to the foundation and superstructure (and can result in the collapse of a pole/column-supported structure). If the structure is small in comparison to the pit, the structure can become unrepairable. Once pit subsidence develops, it may move again (reactivate) in the future. For sag subsidence, the estimation of structural response and associated damage requires a much greater understanding of a complex set of factors. The behavior of a surface structure with respect to sag subsidence depends on the nature of the structure, the ground conditions, and the subsidence characteristics. The nature and magnitude of the induced 26 STRUCTURE magazine
Figure 2. Illustrations of pit and sag/trough subsidence.
building deformation depend on the variation and magnitude of the ambient ground movement (controlled by the characteristics of the sag and the position of the structure within the sag). The induced deformation is also related to the construction of a proposed structure and the condition of an existing structure. Generally speaking, structures that are more flexible, simpler, and smaller react better to sag movements than large structures with rigid and fragile components, especially if the structure is complex and thus more susceptible to stress deformation concentrations. Consequently, even when impacted by the typical range of sag subsidence, structures such as wood barns, sheds, and smaller wood/metal warehouses (without floors) are likely to sustain only minor damage. Figure 3 (page 28) shows the full range of imposed structural deformations that can exist from the compression zone to the tension zone when the sag is large compared to the structure. The induced deformation is a function of the plan orientation, as well as the position of the structure on the sag (or trough) profile. Variations in the ground movement, as well as in construction, make the behavior difficult to model. The structural elements are rarely exposed to a purely two-dimensional state of stress. Moreover, where severe structural deformations are present, significant bending, shear, and tensile and/or compressive strains can be commonly found in the structure. continued on page 28
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For any given subsidence basin, ground, and structure scenario, the relative size and location of the structure with respect to the sag determines the induced foundation strains/stresses and rigid body rotation. When structure area, S, versus the basin area, B, is small (e.g., up to about a small house for larger sags or trough), and assuming typical subsidence conditions, the structure will commonly lie in either the tension or compression zone and may be exposed to maximum slope effects. At small S/B ratios, the ambient ground movements are relatively two-dimensional in the tension zone, while ground deformations in the compression zone are commonly threedimensional, even at small S/Bs. Structures that are relatively small with respect to the subsidence basin have the highest potential for rigid body tilt and translation. For intermediate values of S/B, the subsidence-structure interaction will most Figure 3. A sketch of some deformed flexible blocks resulting from a single sag event over an likely be more complicated. The structure can also span the abandoned mine. slope zone, and both compressive and tensile damage can occur at opposite ends of the structure. At large S/B ratios (e.g. department great, the underlying mine workings can be stabilized. Mine stabilization store size), the foundation and superstructure response will usually be via grouting can be done utilizing various methodologies ranging from three-dimensional with compressive and tensile effects and include sag- significantly reducing to virtually eliminating any subsidence effects, at ging unless the exposure to the basin is small enough under the structure a significant difference in cost. Although relatively inexpensive for unit that a “cantilevered” tensile condition may result. costs, mine stabilization can require massive grout quantities; 20,000 As noted above, building response depends on several variables. to 50,000 cubic yards is not uncommon. However, based on the authors’ experience, noticeable damage can be expected to commence at angular distortion values of 1/250 to Conclusion 1/300 with structural damage on the order of 1/150. An example is provided in Figure 4. In addition to other significant damage, Figure In addressing construction above underground coal mines, questions 4 shows the wall-floor of about 0.7 feet, which occurred in the middle that need to be answered are: What is the risk of subsidence over the of an apartment building, on the third floor, from hogging curvature lifespan of the structure? What is the amount of movement that can of the subsidence profile. The angular distortion of the subsidence occur? What is the potential damage? What can be done to mitigate profile over the span of this building reached about 1/90. the risk? The risk decision-making process involves understanding and evaluating the likelihood of subsidence and associated consequences. Therefore, given the investment, having corMitigation Measures rect risk information is critical to proper decision making.■ The subsidence damage risk can be controlled by taking surface and/or subsurface measures to reduce the potential damage. Surface measures Dr. Marino is a nationally known expert in mine subsidence engineering include moving to a preferable structure orientation/location, earth presand the President of Marino Engineering Associates, Inc. (MEA). sure reduction design, stress/strain resistant and compliant design, and (gmarino@meacorporation.com) tilt accommodation. In most cases, however, the subsidence-resistant Dr. Osouli is an Associate Professor at Southern Illinois University design is not the most cost-effective alternative when exposed to more Edwardsville and Senior Consultant. (aosouli@siue.edu) typical movements. Where the potential subsidence damage risk is too
Figure 4. Three-story apartment building subjected to severe mine subsidence.
28 STRUCTURE magazine
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CODES and STANDARDS AASHTO Vehicle Live Loading Past, Present, and Future By Linda Kaplan, P.E.
T
he American Association of State Highway and Transportation Officials Load and Resistance Factor
Design code (AASHTO LRFD) guides modern highway bridge design. The code includes prescriptive criteria for vehicular live load covering individual truck loads, lane loads, the likelihood of multiple lanes of traffic containing high truck loads simultaneously, and impact loading. Additionally, state-specific codes allow for special permit vehicles based on local conditions and needs. The current AASHTO live loads were put into practice in 1996, the latest in a series of updates developed to represent modern traffic and design practices.
Development of AASHTO Live Loads The first written specifications for bridge design in the U.S. can be traced to railroad companies in the early 1870s. Previous to that, highway and railroad bridges were to meet simply stated criteria specific to the expected use and span length of the structure, usually by private investors teamed with engineers. For example, John Roebling’s 1846 Suspension Bridge to carry highway traffic over the Monongahela River in Pittsburgh, PA, was specified for: Weight of the superstructure supported by cables Four 6-horse teams, loaded with 104 bushels of coal Weight of 100 head of cattle As the need for highway bridges expanded, so did the need for consistent guidelines and design criteria. Individual engineers were interested in addressing the need for design standards. Theodore Cooper, previously best known as the chief inspector on the Eads Bridge over the Mississippi River, published his General Specifications for Steel Highway Bridges and Viaducts in 1884, followed by his Specification for Highway Bridges in 1890. Considered the “first authoritative specification… published and circulated,” Cooper's publications were frequently sighted as the basis of future codes and standards. The American Railway Engineering Association (AREA, now AREMA), the American Association of State Highway Officials (AASHO, now AASHTO), and ASCE all worked on this issue – each developing separate guidelines in the early 1920s before coming together in 1924
Figure 1. Specifications for Steel Highway Bridges (Conference Committee) for truck trains and equivalent loads.
when representatives of each, as well as the American Institute of Steel Construction (AISC), met, forming the Conference Committee and publishing the Specifications for Steel Highway Bridges in 1928. The Specifications only addressed vehicular traffic as the primary source of transportations for urban areas. No discussion was included for trolley loads or shared structures which were common in many cities. Three traffic classes with associated “truck trains” representative of a line of trucks, and equivalent loads, were included. The “H” trucks defined here are the predecessors of the modern “HS” and “HL” loading definitions in today’s code (Table 1). Following the Conference Specifications, the first edition AASHO Standard Specifications for Highway Bridges and Incidental Structures was published in 1931, with the same live load definitions (Figure 1). It was not until the 3rd edition, published in 1941, that significant changes were made. Bridge classification was eliminated, the “equivalent” load was changed to “lane” Table 1. Traffic classes form the 1928 Conference Specification. load, the HS truck (which represented a truck with Traffic Live Load / a semitrailer) was defined, and the truck train was Class Description Truck replaced by either a single design truck per lane or AA Frequent heavy traffic with regular higher loads H-20 the lane loading. The 4th edition in 1944 contained additional changes, including modification of the A Normal heavy traffic with occasional higher loads H-15 HS truck to have variable axle spacing, modificaB Temporary or semi-temporary structures with light traffic H-10 tions to lane loads to better suit continuous spans, 30 STRUCTURE magazine
and a change in nomenclature adding the development year to the truck designation. Few changes were made from the mid-1940s until the development of new live load models for the AASHTO LRFD code in the 1980s. Current bridge live loads and design are based on the 1994 AASHTO LRFD code and remain basically unchanged since then.
expected percentage of truck traffic on the structure. Two traffic conditions were considered in Number of Multiple this development: Loaded Lanes Presence Factor • Random traffic moving with highway speed 1 1.20 in which the site average number of trucks 2 1.00 is observed, evenly distributed across the structure, and are separated by an average 3 0.85 number of cars. >3 0.65 • Traffic jams, with trucks moving at a slow or crawling speed in which the trucks are likely Current AASHTO Live Load to be traveling primarily in one lane while In the 1980s and early 1990s, it became clear cars utilize the others. that the HS20 vehicle used in design was not a Truck behavior was taken from survey data good representation of current highway loading from the Michigan Interstate Highways and and that a new design model was needed. Five combined with engineering judgment to develop candidate loads were developed and modeled additional influence surface models. For examusing influence line analysis to look at the maxiple, limited observation suggested that, with two mum positive bending moment, maximum shear lanes of traffic flowing in the same direction, at supports, and maximum negative moment. about every 15th truck is on the bridge simultaRepresentative bridges consisting of simple neously with another truck in an adjacent lane. spans ranging in length from 10 to 200 feet Based on the modeling, the multiple presence and two-span continuous structures with equal factors in Table 2 were developed and are to be spans, also ranging from 10 to 200 feet, were applied to the live load. modeled. The goal was to determine which of Figure 2. HL-93 live load vehicle. These factors were based on modeling that the candidate vehicles would produce the most assumed an Average Daily Truck Traffic (ADTT) consistent results so that a single live load model could be utilized of 5,000 trucks in one direction. For low traffic structures with an for all structure types and lengths. ADTT between 100 and 1,000, 95% of these values may be used. The selected and current AASHTO live load vehicle is designated For extremely low truck areas with ADTT less than 100, 90% of HL-93, and loading consists of a combination of the design truck these values may be used. or design tandem with the design lane load, specified to produce Modern live load analysis for bridge structures typically utilizes the extreme force effect. The total vehicle weight is 72 kips with the design software to determine the worst-case loading. Thousands of axle weights and spacing of the design truck as shown in Figure 2. individual load cases can be considered on a structure to calculate the The spacing between the two 32.0-kip axles varies between 14.0 feet worst possible force effects on the bridge. The analysis will include and 30.0 feet. load cases with the lane load covering single lane loading, multiple The design tandem, representing two trailers in series attached to lane loading, single-span loading, and multi-span loading. For each one truck, consists of a pair of 25.0-kip axles (50-kip total vehicle condition, the truck point loads are moved throughout the loaded weight) spaced 4.0 feet apart, with the transverse spacing of wheels area to determine the location causing maximum shear and maximum set as 6.0 feet. The design lane load consists of a load of 0.64 klf positive and negative moment in the component being designed. No uniformly distributed in the longitudinal direction. See Figure 3 for single load case will control the overall design of the structure. the loading diagrams. Transversely, the design lane load is assumed to be uniformly distributed over a 10.0-foot width. The force effects The Future of Live Load Models from the design lane load are not subject to a dynamic load allowance. Additionally, many states have designated Permit Vehicles required As it has now been over 25 years since the live load truck models for design, which place higher loads on the structure to account for currently used in design were developed, the question arises if these common local industry needs. The maximodels are still applicable to modern mum legal load is the same for all states traffic patterns and vehicle designs. To at 80 kips, while permit loads vary quite investigate this, the Federal Highway a bit with maximums up to 110 kips. Administration (FHWA) has started to Application of the permitted load varies collect data on vehicle weight, frequency, by state with some requiring permit loads and axle arrangements in various parts of to be analyzed similarly to the HL-93, the country. By looking at representative and others allowing them to be a sepasamples of Weigh in Motion (WIM) rate load case, assuming no or limited data obtained as part of the ongoing other traffic will be on the structure at studies, one can start to get a sense of the same time. how current conditions compare to When adapting the developed loading design standards. to long-span and multi-lane structures, Data obtained from interstate highway it was recognized early on that the likelibridges around metropolitan areas in hood of a bridge completely packed with Oregon and Georgia provide a basis for trucks was low, so factors were necessary quick comparisons and justification for to account for multi-lane traffic and the Figure 3. Lane and truck loading combination diagram. further study. Seasonal changes in traffic Table 2. Multiple presence factors.
APRIL 2020
31
Table 3. Representative samples of weigh in motion data.
Month
Total Vehicle Count
# Over 72 Kips
# Between 50 and 72 kips
Average Vehicle Weight (kips)
Approx. Lane Load (assumes 30 feet between vehicles)
April 2018
272,427
25,656, (9%)
21,921 (8%)
20,783
0.693 k/ft
October 2018
292,834
20,245 (7%)
21,653 (7%)
17,964
0.599 k/ft
April 2018
1,617,011
53,701 (3%)
43,243 (3%)
11,038
0.370 k/ft
October 2018
1,048,575
30,766 (3%)
39,936 (4%)
11,122
0.371 k/ft
State Oregon Georgia
are to be expected, so a year’s worth of data is required for complete analysis. However, a sample of the data looking just at April and October 2018 was analyzed using metrics of Gross Vehicle Weight (GVW) and average vehicle weight for demonstrative purposes (Table 3). Data related to axle weight, axle spacing, vehicle spacing, speed, and frequency were also collected but have not been included here. Looking individually at the data from Georgia would imply that the current design criteria fit observed traffic reasonably well. Only 3% of the vehicles observed are over the design GVW, which could easily be explained by state permit loads. Additionally, the approximate lane load is well below the 0.640 k/ft used in design. However, looking at the Oregon data is less reassuring. With up to 9% of the observed vehicles over the design load and an additional 7% over the design tandem load, it appears that a more substantial design load may be called for. The lane load observed in this data set also approaches or exceeds the design lane load, again implying that higher design loads may be justified. Traffic loads are likely to change significantly in the not-to-distant future as autonomous vehicles, both cars and trucks, become more common. The possibility of driverless, long truck trains, moving in close formation and high speeds, and the significantly higher load potential
they present, has not yet been considered. As this becomes a reality, both codes and existing infrastructure will need to be carefully reevaluated.
Conclusion Bridge live load modeling as prescribed in the AASHTO LRFD code has developed over the past century to account for vehicle changes, advances in modeling techniques, and new and better data on existing traffic. As traffic continues to evolve, it is both timely and appropriate that the FHWA is again looking into this matter. Preliminary data indicates that changes may be called for and validates the effort involved in the studies.■ The online version of this article contains references. Please visit www.STRUCTUREmag.org. Linda Kaplan is a Structural Project Engineer with Pennoni Associates in Pittsburgh, PA. She is a co-author of the book, Bridges... Pittsburgh at the Point... A Journey Through History. (lkaplan@pennoni.com)
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32 STRUCTURE magazine
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Trimble Phone: 678-737-7379 Email: jodi.hendrixson@trimble.com Web: www.tekla.com/us Product: Tekla Structures Description: Can be used for wood framing: True BIM model of wood framing; parametric components allow for easy creation and design change; easily add or move doors and windows; library of industry standard wood connections included; clash checking functionality to eliminate change orders; easily customizable to suit any job requirements. Product: Tekla Tedds Description: Using Tekla Tedds you can design a range of wood elements, and produce detailed and transparent documentation for beams (single span, multi-span and cantilever), wood columns, sawn lumber, engineered wood, glulam and flitch options, shear walls (multiple openings: segmented or perforated) and connections (bolted, screwed, nailed, wood/wood and wood/steel).
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34 STRUCTURE magazine
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NCSEA
NCSEA News
National Council of Structural Engineers Associations
Invitation to Participate in the 2020 SE3 Survey The NCSEA Structural Engineering Engagement and Equity (SE3) Committee is currently administering its third nationwide survey of structural engineers across the profession and we invite you to participate! The SE3 Committee is composed of a diverse group of engineers across the United States. Our mission is to attract and retain the best and brightest into our profession; and to ensure ALL structural engineers have a clear pathway to success. The SE3 survey is an ongoing effort to identify trends, understand the underlying factors, and initiate industry-wide conversations. For example, did you know that roughly 60% of survey respondents have considered leaving the profession at some point in their career? When comparing a respondent's years of experience with their inclination to stay until retirement, the 2018 survey identified three (3) career pinch-points – occurring at year two (2), ten (10), and eighteen (18) years. Based on key survey findings, the committee utilizes presentations, panel discussions, and networking events to provide actionable information for industry improvement. Survey topics include career development, compensation, work flexibility, and overall engagement. For more information, including past events and publications, check out www.SE3committee.com. The SE3 Committee looks forward to your participation! Join the conversation and participate in the 2020 SE3 survey – look for the link on the SE3 website or www.ncsea.com/committees/se3.
Now Accepting Nominations for NCSEA Special Awards
NCSEA's Special Awards are presented each year at the Structural Engineering Summit. These awards are presented to NCSEA members who have provided outstanding service and commitment to the association and to the structural engineering field. Special Awards are granted to worthy recipients in four different categories: The NCSEA Service Award is presented to an individual who has worked for the betterment of NCSEA to a degree that is beyond the norm of volunteerism. It is given to someone who has made a clear contribution to the organization and therefore to the profession. 2019 Recipient: Ben Nelson, P.E. The Robert Cornforth Award is presented to an individual for exceptional dedication and exemplary service to a Member organization and to the profession. 2019 Recipient: Thomas A. DiBlasi, P.E., SECB
The Susan M. Frey NCSEA Educator Award is presented to an individual who has a genuine interest in, and extraordinary talent for, effective instruction for practicing structural engineers. 2019 Recipient: Dr. S.K. Ghosh The James Delahay Award is presented at the recommendation of the NCSEA Code Advisory Committee, to recognize outstanding individual contributions towards the development of building codes and standards. 2019 Recipient: Kelly E. Cobeen, S.E.
Visit www.ncsea.com to submit your nomination by June 23, 2020.
Don't Miss This Month's Training to Become a Second Responder Register for the next NCSEA CalOES Safety Assessment Program on Wednesday, April 29, 2020
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. Doug Fell, P.E., Structural Resource Center LLC, is a CalOES Assessor, Coordinator and Instructor. Doug is the managing principal of Structural Resource Center LLC. He was the lead structural engineer for the Minneapolis Metrodome roof collapse stabilization and return to service. Doug is the chairperson of the Minnesota SEA SEER Committee and is the MNSEA SEER member organization representative on the NCSEA SEER Committee. Register by visiting www.ncsea.com. This course is not included in the Live & Recorded Webinar Subscription. 36 STRUCTURE magazine
News from the National Council of Structural Engineers Associations L’EGGO MY EGGO By Sarah Kay Twine
The Structural Engineers Association of Arizona (SEAoA) hosted their 2nd Annual Egg-Drop Competition and Fundraiser in January at the University of Arizona. The competition serves to raise money for SEAoA's Annual Student Scholarship given to University of Arizona structural engineering students, and to provide a networking opportunity for professionals and students in the fields of engineering, architecture, and construction. The evening was a fun-filled egg-citing way for teams to take on the great challenge of creating an apparatus to protect a raw chicken egg from cracking when dropped from the 35-foot second landing of the Civil Engineering courtyard staircase. Each team, consisting of two professionals and one or two students, was given a bag of the same materials and had only twenty minutes to hatch an idea and create a device to protect their egg. The competition is intended to parallel the structural engineering world: protect the public (the egg) and provide an economical (light weight) design. Some teams designed a parachute to slow the fall while others chose materials to absorb the impact. A few decided to combine both concepts. As the deadline approached, some teams were scrambling to finish while others patiently waited to show off their design. All teams had great egg-spectations for their personal creations. After time was up, each device was weighed before it was dropped. The winner would be the lightest device to sustain the drop resulting in an unbroken egg. Applause filled the courtyard after each team had "l'eggo their eggo" from the landing. A judge determined whether each egg was un-cracked, cracked (no leaking), or completely obliterated. After 13 dropped eggs, 6 were un-cracked, 4 were cracked, and 3 had been annihilated. Team 5 crushed the competition with an apparatus weighing 79 grams (31 grams less than the previous year’s winner). The winners included two University of Arizona civil engineering students: Adam Bishop and Sergio Corona, and two Professionals from M3 Engineering and Technology Corp.: Allan Ortega and Austin Urton. The winners each received a $50 Amazon Gift Card. The event was a huge success, and approximately $1150 was raised for the students! SEAoA would like to extend a special thank you to the University of Arizona ASCE Executive Team and Jessica Carson, S.E., from Martin, White & Griffis, for creating this event last year and lending a hand this year.
SEAs Participate in E-Week
SEAOI (left) and SEAoAL (right) each demonstrated seismic activity to budding SEAW assisted students with a variety of OSEA's Young Member group testing interactive activities, including building students' structures during a bridge structural engineers with their shake tables. gumdrop towers. breaking competition.
NCSEA's Communication Committee has developed many resources to help members take the first step in reaching out to their local schools to share the profession and how students can start their career plans. These valuable resources include many hands-on activities, the step-by-step High School Outreach Start-Up Guide, and the What is Structural Engineering PowerPoint presentation. These resources have aided local NCSEA Member Organizations in the creation of impactful outreach programs as well as successful e-week activities. For more information about NCSEA's STEM resources, visit www.ncsea.com.
NCSEA Webinars
Register by visiting www.ncsea.com
April 16, 2020 Structural Design and Embodied Carbon Nicholas Miley, S.E.
April 23, 2020 Rain Loads – The Forgotten Hazard Michael O’Rourke, P.E., Ph.D.
Courses award 1.5 hours of Diamond Review-approved continuing education after the completion of a quiz. A P R I L 2 02 0
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SEI Update Advancing the Profession
Congratulations to the 2020 ASCE Structural and SEI Award Recipients SHORTRIDGE HARDESTY AWARD Ben Young, Ph.D., M.ASCE
JACK E. CERMAK MEDAL Peter J. Vickery, Ph.D., P.E., F.SEI, F.ASCE
NATHAN M. NEWMARK MEDAL Satish Nagarajaiah, Ph.D., F.SEI., F.ASCE
RICHARD R. TORRENS AWARD Anil Agrawal, P.E., Ph.D., M.ASCE
W. GENE CORLEY AWARD Randall P Bernhardt, P.E., S.E., F.SEI, F.ASCE
WALTER P. MOORE, JR. AWARD Charles A. Kircher, Ph.D., S.E., M.ASCE
DENNIS L. TEWKSBURY AWARD Donald Dusenberry P.E., SECB, F.SEI, F.ASCE
JACK E. CERMAK MEDAL Kenny Kwok, Ph.D., CPEng, M.ASCE
SEI PRESIDENT’S AWARD David W. Cocke, S.E., F.SEI, F.ASCE
RAYMOND C. REESE RESEARCH PRIZE Dan Mircea Frangopol, P.E., F.SEI, Dist.M.ASCE, and Yan Liu, Ph.D., A.M.ASCE
MOISSEIFF AWARD Tsukasa Mizutani, Tomonori Nagayama, Ph.D., A.M.ASCE, Tomoaki Takeda, Ph.D., and Yozo Fujino, Ph.D., M.ASCE
SEI CHAPTER OF THE YEAR AWARD SEI Houston Chapter
SEI GRADUATE STUDENT CHAPTER OF THE YEAR AWARD SEI Graduate Student Chapter (GSC) at Northeastern University
Nominate for 2021 SEI/ASCE Awards at www.asce.org/SEI.
SEI Online
Are you on Social Media? Follow SEI on Linked In, Twitter, Facebook, YouTube, and now Instagram too!
SEI News Read the latest at www.asce.org/SEINews SEI Standards Visit www.asce.org/SEIStandards to view ASCE 7 development cycle 38 STRUCTURE magazine
News of the Structural Engineering Institute of ASCE Learning / Networking
ASCE Guided Online Course: Seismic Analysis of Building Structures April 27 – July 17, 2020
• Understand the theoretical basis and the appropriate methodology for implementing three primary seismic analysis methods needed to determine the seismic force and deformation demands in ASCE 7 for building structures and nonbuilding structures. • Enhance structural analysis skills for engineers who design structures for seismic loads. • Apply equivalent static and linear dynamic analysis methods for the determination of seismic demands. www.asce.org/seismic-analysis-of-building-structures
Save the Date and Call for Proposals
Submit abstract and session proposals by June 3, 2020, related to the full lifecycle of structures to advance structural engineering through: Leadership Development | Project Solutions | Emerging Technology | Resilience | Sustainability | Functional Recovery | Global Climate Change | Innovative Research with Practical Application Sponsor/Exhibit and reach more than 1,000 industry professionals. Contact Sean Scully at sscully@asce.org www.structurescongress.org #Structures21
What distinguishes Structures Congress from other conferences? By J. Greg Soules, P.E., F.SEI, F.ASCE, Chair of SEI NTPC, Senior Principal, McDermott
The annual SEI Structures Congress covers all materials used in structures (steel, concrete, masonry, and timber) along with foundations, special loadings (blast, fire, seismic, wind, etc.), code issues, and professional issues such as licensing, liability, and other legal issues. Additionally, we have topics related to all types of structural research and education issues. The more than 1,000 participants at Structures Congress generally specify materials and equipment. The SEI National Technical Program Committee (NTPC) is an SEI Board-level committee responsible for organizing the technical program and is made up of 20 volunteer structural engineer members from government, private practice, industry, and academia along with two SEI staff members. The goal of NTPC is to provide the best possible program to attract practicing structural engineers and academics from around the world, provide a forum to exchange knowledge, and support the growth and development of the structural engineering profession. NTPC volunteers represent all areas of structural engineering practice and academia. Structures Congress involves all areas of structural engineering, including: • Blast and Impact Loading • Bridges, Tunnels, and other Transportation Structures • Buildings
• Business and Professional Practice • Career Development • Education • Forensic
• Natural Disasters • Nonbuilding and Special Structures • Nonstructural Components and Systems • Innovative Research
Each year, NTPC receives more than 600 presentation abstracts through an open call and invites abstracts on specific topics and those related to the location of Structures Congress that year. Peer review papers are not required. The technical program is highly competitive, generally accepting less than half of the abstracts submitted. While the technical program includes both practice and academic topics, it is weighted toward practicing structural engineers since the majority of the 30,000 SEI members are in practice.
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. A P R I L 2 02 0
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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 or keep track of the skills young engineers are learning at each level of experience, CASE has the tools you need! The following documents/templates are recommended to review/use if your firm needs to update its current Quality Assurance Program, or incorporate a new program into the firm culture: 962: 962-B: 962-C: 962-D: Tool 1-2: Tool 2-1: Tool 2-4: Tool 4-1: Tool 4-2: Tool 4-3:
National Practice Guidelines for the Structural Engineer of Record (2018) National Practice Guideline for Specialty Structural Engineers Guidelines for International Building Code Mandated Special Inspections and Tests and Quality Assurance Guideline addressing Coordination and Completeness of Structural Construction Documents Developing a Culture of Quality Risk Evaluation Checklist Project Risk Management Plan Status Report Template Project Kick-off Meeting Agenda Sample Correspondence Letters
Tool 4-4: Tool 4-5: Tool 9-2: Tool 10-1: Tool 10-2:
Phone Conversation Log Project Communication Matrix Quality Assurance Plan Site Visit Cards Construction Administration Log
You can purchase these and the other Risk Management Tools at www.acec.org/bookstore.
CASE Winter Member Meeting Update Previously, CASE has brought their committee members together for a day-long working session with a roundtable the night before. This year, along with three other ACEC Coalition groups, CASE developed an education meeting with some strategic planning in the afternoon. Held February 27-28 in New Orleans, LA, this meeting had several education sessions ranging from an internal ethics case study done by legal counsel of Terracon to an interactive technology panel with representatives from Autodesk, BST Global, and Newforma. During the afternoon of the 28th, break-out sessions were held by the CASE Contracts, Guidelines, Toolkit, and Programs & Communications Committees to work on advancing some strategic initiatives and engaging members even further in discussions. Current initiatives include: I. Contracts Committee – Bruce Burt (bburt@rubyandassociates.com) • The committee is working on updates to the three commentaries that correspond to AIA contract documents. • Exploring new design-build area within CASE along with CASE Guidelines and Toolkit committees II. Guidelines Committee – Kevin Chamberlain (kevinc@dcstructural.com) • Exploring new design-build area within CASE along with CASE Contracts and Toolkit committees • Working on the following new documents: º Introduction to Seismic Engineering for the Practicing Structural Engineer º Structural Engineer’s Guide to the Procurement, Use, and Implementation of Geotechnical Engineering º Beyond the Code – Understanding Client Expectations and Strategies for Managing Them III. Programs and Communications Committee – Nils Ericson (nericson@m2structural.com) • Discussed options for sessions at the 2020 ACEC Fall Conference 40 STRUCTURE magazine
• Discussed options for a session to submit for the 2021 SEI Structures Congress • Discussed joint CASE/NCSEA Business of Structural Engineering Workshop IV. Toolkit Committee – Roger Parra (rparra@degenkolb.com) • Exploring new design-build area within CASE along with CASE Contracts and Guidelines committees • Working on the following updates to current tools: º Tool 2-5: Insurance Management º Tool 3-1: A Risk Management Program Planning Structure º Tool 6-2: Scope of Work for Engaging Sub-consultants º Tool 8-1: Contract Review º Tool 8-2: Contract Clauses and Commentary • Working on the following new document topics: • Job Descriptions • Succession Planning • Employee Retention The next Member Meeting will be held summer of 2020. Please contact Heather Talbert (htalbert@acec.org) to be added to the pre-registration listing.
News of the Coalition of American Structural Engineers CASE Practice Guidelines Currently Available CASE 976-C – Commentary on 2010 Code of Standard Practice for Steel Buildings and Bridges The 2010 COSP addresses many recent changes in the practice of designing, purchasing, fabricating, and erecting structural steel and is, therefore, a continuation of the trend of past improvements and developments of this standard. It is important to note that the Structural Engineer can change any of the requirements of the Code of Standard Practice by specifying an alternative in the Contract Documents. This document discusses the list of changes published in the preface of the 2010 Edition and provides some commentary to these changes. This document also addresses areas of the COSP that may not be well understood by some SERs but will likely have an impact on the structural engineer’s practice of designing and specifying structural steel. CASE 976-D – Commentary on 2010 & 2015 Code of Standard Practice for Steel Joists and Joist Girders This commentary provides observations and analysis of the revisions and additions in both documents and discusses specific aspects of the COSP that have a direct impact on the structural engineer’s practice of specifying steel joists. A familiarity and understanding of the entire SJI
COSP are necessary to ensure the proper design and documentation of steel joists and Joist Girders. However, the discussion highlights sections of interest to the specifying structural engineer. CASE 976-E – Commentary on ASCE Wind Design Procedures The purpose of this Guideline is to provide guidance and commentary on the wind provisions of ASCE/SEI 7, and provide a brief overview of the changes from ASCE/SEI 7-05 to ASCE/SEI 7-10, and again from ASCE/SEI 7-10 to ASCE/SEI 7-16. One helpful aspect of the restructured wind provisions is that each part of each analysis procedure contains a step by step checklist of items that need to be determined for that given procedure, along with references to Figures, Tables, and Equations in which those parameters can be determined. The changes in wind design procedures and chapter formatting from ASCE/SEI 7-05 to ASCE/SEI 7-10 were very extensive. The changes from ASCE/SEI 7-10 to ASCE/SEI 7-16 were minor in comparison and were noted with solid grey lines in the margins of ASCE/SEI 7-16. You can purchase these and the other CASE Risk Management Tools at www.acec.org/bookstore.
Donate to the CASE Scholarship Fund! The ACEC Coalition of American Structural Engineers (CASE) is currently seeking contributions to help make the structural engineering scholarship program a success. The CASE scholarship, administered by the ACEC College of Fellows, is awarded to a student seeking a Bachelor’s degree, at minimum, in an ABET-accredited engineering program. Since 2009, the CASE Scholarship program has given $35,000 to help engineering students pave their way to a bright future in structural engineering. We have all witnessed the stiff competition from other disciplines and professions eager to obtain the best and brightest young talent from a dwindling pool of engineering graduates. One way to enhance the ability of students to pursue their dreams to become professional engineers is to offer incentives in educational support. Your monetary support is vital in helping CASE and ACEC increase scholarships to those students who are the future of our industry. All donations toward the program may be eligible for a tax deduction, and you don’t have to be an ACEC member to donate! Contact Heather Talbert at htalbert@acec.org to donate.
CASE Member Firms Win Engineering Excellence Grand, Honor Awards Congratulations go out to the following CASE Member firms for winning Grand Awards: Thornton Tomasetti, The Shed in New York, NY Magnusson Klemenic Associates, Inc., Amazon Urban Neighborhood in Seattle, WA These firms are finalists for the Grand Conceptor Award being awarded at the 53rd Engineering Excellence Awards Gala April 28th in Washington, DC, as part of the ACEC Annual Convention. CASE Member Firm raSmith won an Honor Award for their project, University of Wisconsin-Madison Hamel Music Center, in Madison, WI.
Follow ACEC Coalitions on Twitter – @ACECCoalitions. APRIL 2020
41
legal PERSPECTIVES Warning Flags for Structural Engineers Watch for Ten Hidden Risks in Contracts By Robert Hughes
T
oday, more owners and other project participants are looking for ways to transfer risk to engineering firms by inserting potentially onerous language in contracts. In many cases, such contractual exposures are not insurable under an engineering firm’s professional liability insurance or other policies, leaving the firm with potentially substantial uninsured exposures. Here are ten contractual issues that engineers should flag, discuss with their legal counsel and insurance advisor, and either address in the final version of the contract or be prepared to make informed business decisions on how to proceed.
Indemnification Language 1. Duty to defend. A key contractual pitfall for engineers involves the inclusion in an indemnity agreement of an obligation to “defend” a client from claims made by third parties. This affirmative obligation is not insurable under professional liability policies. Strike any reference to an obligation to defend a client; as a back-up, agree to reimburse defense costs in your proportionate share and as recoverable under common law (do not include legal fees or costs for enforcing the indemnity obligation itself ). 2. Tied to negligence. Many indemnification clauses require the engineer to indemnify the project owner or client for “any and all claims arising out of ” the engineer’s services, without regard to negligence. Modify this language so: 1) it is tied to the engineer’s negligence, and 2) you agree to indemnify a client only for third party claims. Also, be sure that a finding of some degree of negligence on your part does not then trigger an obligation to indemnify the owner or client for their percentage of fault. 3. Indemnifying entities related to the owner. Often, clients insert language requiring engineers to indemnify entities that may be “related” to the actual client in the contract. This may include agents, representatives, subsidiaries, affiliates, other consultants, and lenders, all creating insurability issues. Strike any references to parties or agents beyond your client, its officers, and its employees. 42 STRUCTURE magazine
Standard of Care 4. Expansive wording. When defined in the contract, the standard of care should require the engineer to “... perform its services within the degree of skill and care ordinarily exercised by other members of the same profession practicing in the same locality and under similar circumstances as of the time services were rendered.” Watch for language altering the standard, such as requirements for the engineer to exercise its “best efforts” or the “highest” degree of care, or that allows the client to make unilateral determinations as to the quality of your services. Further, your contract never should promise perfection or total accuracy in your professional services; that might be interpreted as a warranty or guarantee, both of which are excluded under most professional liability policies. 5. Agreeing to act in a fiduciary capacity. If a client inserts a sentence in the contract that reads “consultant will act at all times in the best interests of the client” or refers to there being a fiduciary duty owed by the consultant, this is “disguised” standard of care language. Strike any language referring to a fiduciary relationship or that requires you to act at all times in the client’s best interest.
General Contractual Issues 6. Waiver of consequential damages. Consequential or special damages are indirect economic expenses, such as lost profits and elements of delay damages or diminution in value. Although potentially insurable, consequential damages represent a disproportionate risk to the compensation provided to the professionals in the engineering contract. Try to reject language holding you responsible for consequential damages and consider adding a clause to waive that responsibility. 7. Site safety. Contracts should include a safety clause, making job site safety the sole responsibility of the contractor and excluding the engineer from any related obligation such as site supervision. By written agreement, the project owner should require the contractor to name the engineer as an additional insured under the contractor’s commercial general liability and auto policies.
8. Ownership of documents. Strike contractual language that offers a client unlimited license to use the A/E firm’s instruments of professional services; instead, contracts should only provide a limited license for the client’s specific project needs. If this is not possible, secure a waiver and indemnity from your client for any subsequent use or re-use of your work product. 9. Retaining consultants historically hired directly by the owner. Owners traditionally hire an A/E firm to design their project, with the firm then hiring various subconsultants. However, some services, such as geotechnical engineering and environmental investigations, are traditionally independently retained by the owner, outside the prime engineer’s responsibilities. Today, more contracts seek to have the prime consultant retain all subconsultants on the project (often including firms selected by the owner). You should not agree to this; if you hold the contract, you are liable for their negligence. 10. No right to rely on owner-supplied information. In any project, engineers can only complete their work after receiving accurate information and documents from the owner, such as geotechnical reports, as-builts of existent structures, etc. Traditionally, contracts addressed at least two related obligations – one on the owner to furnish accurate information on a timely basis; the other, giving engineers the right to rely on that information. However, there has been an increase in language altering these obligations. Insist on language that obligates the owner to provide timely, accurate information necessary for you to complete your scope of services and to affirm your right to rely on that information. By understanding these hidden exposures, structural engineers will be better positioned to practice good contractual hygiene and have productive, profitable, and mutually rewarding relationships with their clients.■ Disclaimer: The information in this article is for educational purposes only and is not legal advice. Readers should not act or refrain from acting based on this article without seeking appropriate legal or other professional advice as to their particular circumstances. Robert Hughes is Senior Vice President and Partner with Ames & Gough.
APRIL 2020
Learn about the changes in ACI 318-19 Attend one of 25 public seminars titled “ACI 318-19: Changes to the Concrete Design Standard” being held throughout the United States this spring. FREE COPY OF ACI 318-19 FOR ALL SEMINAR ATTENDEES
With ACI 318-19 now 100 pages longer than the previous edition, two industry experts will walk seminar attendees through the new provisions and present major technical changes.
SEMINAR LOCATIONS Albany, NY Baltimore, MD Chicago, IL (Rosemont) Cleveland, OH Dallas, TX Denver, CO Des Moines, IA Detroit, MI (Farmington Hills) Emeryville, CA Houston, TX Indianapolis, IN Little Rock, AR Miami, FL Minneapolis, MN Nashville, TN New Brunswick, NJ
New Orleans, LA Pittsburgh, PA Portland, OR Raleigh, NC Richmond, VA San Diego, CA Savannah, GA St. Louis, MO Tampa, FL
Visit concrete.org/ACI318 for a complete seminar description and all registration information
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