Practice Periodical on Structural Design and Construction

A conceptually intuitive, computationally efficient iterative procedure is formulated to optimize the member sizes of regular steel moment frames under both lateral forces and gravity loads. This procedure aims to maximize the interstory drifts of a steel frame while satisfying code requirements on both individual member strength and story lateral stiffness. A key premise of the present optimization method is that the process of pushing the interstory drift profile of a steel frame toward the code-specified interstory drift limit (i.e., attaining a fully drifted state) is inherently accompanied by a reduction in the total steel weight of the frame. To attain the desired fully drifted state, an iterative scheme for the story-by-story updating of the column and beam sizes is provided. At each iteration, a steel member is resized according to the worst of its strength demand-to-capacity ratio and the interstory drift demand-to-limit ratio. The iterative process continues until the total steel weight of the frame has been reduced to a satisfactory level, and both member strength and interstory drift have met the code requirements. Member sizing optimization of three example steel moment frames with varied complexities is carried out using the present iterative procedure. Numerical results show that an improved frame design can be generated within a few iterations, and that this design compares favorably with the baseline frame design that results from weight minimization by either an exhaustive enumeration or a genetic algorithm. Therefore, the present iterative procedure is an appealing tool for practical design optimization of steel frames.

This paper explores an all-steel design philosophy for flexural bracing requirements in cold-formed steel stud walls that employ mechanical bridging alone without sheathing. The current cold-formed steel design specification requires the brace for a single compression member to have stiffness equal to twice the ideal brace stiffness, but related proposals for braces in multiple stud walls, including brace force accumulation and minimum brace stiffness, have not yet been adopted. Bracing strength and stiffness demands in cold-formed steel-framed walls must be adequate to ensure safety but not overly conservative so that the requirements cannot be practically met. Elastic critical load and second-order elastic analyses are conducted herein to determine an adequate level of stiffness for a single braced compression member and relationships between strength and stiffness for braced multiple studs to that of a single stud. Statistics of measured member imperfections are incorporated to provide an equivalent imperfection for multiple stud walls. Design by second-order analysis is utilized to determine how alternating the direction of studs affects strength and stiffness requirements. For a single-braced compression member, the impact of allowing a minimum of 1.33 times, instead of twice the ideal brace stiffness, is explored as an alternative to current requirements. New design expressions for brace stiffness and strength, incorporating the notion of a minimum brace stiffness, and the equivalent imperfection are provided. The new expressions provide the designer with greater flexibility in developing solutions that meet the necessary stiffness and strength requirements.

This research provides comparative analysis of the impacts and benefits associated with using building information modeling (BIM) on accelerated bridge construction in the Denver metropolitan area. To date, BIM remains a relatively underutilized tool in horizontal construction. BIM has the potential, however, to significantly increase efficiencies, minimize waste, and increase sustainability across infrastructure projects throughout their life cycles. This research studies the impacts of the first implementation of BIM processes on one of two structurally similar concurrent bridge construction projects by comparing metrics related to substructure costs, requests for information, change orders, rework, and schedule. Findings suggest that negative cost impacts of approximately 70% may be associated with the first implementation of BIM during construction. However, additional findings suggest that the use of BIM may facilitate otherwise infeasible complex projects and reduce requests for information and change orders and has the potential to realize cost savings during follow-on projects. Specifically, findings from this case study suggest that BIM may have provided approximately 5–9% cost savings during construction by contributing to reduced change orders and rework. Revealing such impacts and benefits associated with using BIM on transportation infrastructure construction begins to inform the industry and, in particular, organizations such as DOTs and urban transportation districts about potential opportunities related to BIM implementation. Additional and potentially significantly greater benefits may be realized through future BIM-enabled operation and maintenance of such infrastructure. This study provides a valuable first step in motivating the implementation of BIM within and throughout infrastructure asset management and motivates future research related to the use of BIM during infrastructure construction and operation.

Keyed-through tenon (KTT) joints are timber frame joints consisting of a key placed through the tenon, creating bearing against the back side of the mortise. This joint allows greater flexibility in key sizing compared with typical pegged mortise and tenon joints. However, no experimental testing is available to estimate the strength capacity of these joints. This paper measured the strength and stiffness of KTT joints considering differences in wood species, protruding tenon length, and number of keys. A tensile load was applied to a KTT joint similar to previous testing conducted on pegged mortise and tenon joints. Shorter tenon lengths produced brittle failures of the tenon, whereas longer tenon lengths produced ductile bending and crushing of the keys. Yield load values using the 5% offset method could not be determined for the shorter tenon length samples, but the ultimate load values could be used for yield load. Two keys were approximately twice as strong as a single key because of the increased bearing area and the number of tenon shear planes for load transfer. KTT joints with two keys and 11-in. (279-mm) protruding tenons were recommended from this experimental study. Results of KTT joints compared with previously tested pegged mortise and tenon joints with two 1-in. (25-mm) diameter pegs demonstrated that KTT joints with two keys produced stiffer and stronger joints with maximum load values 41% greater than previously tested pegged joints of similar composition. Size limitations and protection of the protruding tenon from damage are important considerations in the design of KTT joints in structures.

This paper presents an analytical model for the determination of the ultimate flexural capacity of steel fiber-reinforced (SFR) concrete rectangular sections and their associated crack width using the principles of strain compatibility and force equilibrium. The proposed model considers an elastic perfect-plastic model for compression and an elastic constant postpeak response of SFR concrete in tension. Unlike other flexural models available in the literature, the proposed model considers in the analysis the random distribution and orientation of steel fibers at a cracked section. The model was verified using existing experimental results, and it fairly predicted the flexural capacity of the SFR concrete beams. A parametric study using the proposed model was conducted to assess the effect of the fiber parameters and the strength of the concrete on the ultimate flexural capacity of a section and its associated crack widths. A normalized design chart is also presented to simplify the analysis procedure, and this can be used in the selection of fiber parameters (volume fraction and aspect ratio) during flexural design of SFR concrete members.

Currently, there is no formula for tie and direct fixation fastener (DFF) spacing. Because the rail does not bend between the tie/DFF, it is not possible to calculate spacing by the bending stress formula. Usually, rail-stress analysis confirms a trial spacing. Such analysis may support a longer spacing that might not address issues related to load distribution, pressure on formation, torsional rigidity, noise, and vibration. Thus, tie spacing is formulated from the perspective of wheel-load distribution and load dispersion by ballast, considering the fact that ties under the Benkel beam support the vertical load. The DFF/tie spacing is related to the characteristic length of the track, and this study shows that the desired DFF/tie spacing should be less than the characteristic length. Codes and practical examples validate spacing formulated for DFFs, concrete ties, and wood ties.

There appears to be confusion regarding how to conduct a comprehensive benchmarking study, especially one on labor productivity. This paper details a six-step procedure for conducting a labor productivity benchmarking study. The procedure addresses the questions of how, who, and why. The procedure is illustrated using three case study projects. A labor productivity study has several unique features. First, the objective must be precisely defined. A study of labor productivity can be done for many reasons, and the purpose must be clearly defined because the objective influences subsequent decisions involving protocols. Procedures for how the study will be conducted to assure valid comparisons must be developed. Next, the key performance indicators (KPIs) must be determined and a procedure must be established for evaluating multiple KPIs. Labor productivity is unique in that there is no single KPI that can be used to define best performance. Multiple KPIs are proposed and procedures are developed. Once a procedure is developed for evaluating multiple KPIs, data are collected and the best performer is identified. The last question is, “why is a project/activity/entity the best?” This question is often ignored in most so-called benchmarking studies. Once the best project/activity/entity is identified, principles can be summarized as a prescription for productivity improvement.

National organizations have been making efforts to implement a more integrated practice environment, as exemplified by ASCE’s aspirations shared in their vision documents or the American Institute of Architects’ launching of Integrated Project Delivery. Because architectural projects are a substantial portion of construction spending, structural engineers would benefit by increasing their integrated design skills. However, little attention has been given to the structural engineer’s role in integrating architectural design priorities with structural design priorities. A qualitative research study was launched to learn more about the components of integrated design and interviews were conducted with 84 architectural and structural practitioners. Based on the findings, there is a craft to architecturally based structural engineering, especially when the goal is integrated design. Structural engineering participation in integrated design processes was examined and the characteristics were identified, including the qualities of engineering design for architecture, the approach taken by the engineer, iterations strategies, and graphic communication skills. By understanding how engineers work collaboratively and the challenges to integrative design, structural engineers can improve the quality of their professional relationships and tailor their contributions more effectively.

To assist utilities in making well-informed maintenance decisions, the EPA has developed an innovative technology demonstration program to evaluate technologies that have the potential to reduce costs and increase the effectiveness of the operation, maintenance, and renewal of aging water distribution and wastewater collection systems. Under this initiative, the performance of a new corrosion-resistant fiber-reinforced geopolymer mortar was evaluated. The fiber-reinforced geopolymer mortar was spray-applied to rehabilitate a preselected 49-m-long, 1,500-mm (160-ft-long, 60-in.) RC pipe (RCP) sewer main in Houston, Texas. Costing approximately $1,300–$2,000 per linear meter ($400–$600 per linear foot), a 84-mm-thick (3.3-in.) layer was sprayed uniformly onto the pipe’s interior, surpassing the minimum design thickness value of 48 mm (1.9 in.). The average 28-day compressive strength results of the coating were measured to be approximately 59 MPa (8,635 psi), which is above the manufacturer-stated claim of 55 MPa (8,000 psi) at 28 days. The postlining inspection via closed-circuit television (CCTV) showed a successful rehabilitation with no signs of infiltration, exposed rebar, cracking, or any significant defects. In addition, the project resulted in a carbon footprint of an estimated 60% less than an equivalent excavation project.

This paper presents novel and cost-effective design procedures for rectangular hollow steel sections (RHSS) subject to combined compression and major and minor axis bending. Although this loading pattern is very common in practice, very little research has addressed the local stability of RHSS for this loading condition. Furthermore, current North American and European design provisions ignore rotational and lateral restraints in evaluating local web buckling stress of RHSS. This paper provides an analytical closed-form expression to compute web buckling stress with rotational and lateral restraints under compression and biaxial bending. The accuracy of the expression is compared numerically and with existing expressions for the limiting simply supported condition. The maximum difference was found to be less than 2%. The behavior of standard RHSS is also reexamined. Guidelines are also provided for practicing engineers and steel fabricators to optimize the design of RHSS.

A case study on the analysis of an existing trunnion girder and its greased posttension anchors before load testing is presented herein. The analysis, which evaluates the member’s capacities using a finite-element model, also investigates the probability of a critical (nonredundant) anchor failing using test data recorded from both nondestructive dispersive wave propagation testing and load testing of similar anchors at other dams. The results of the analysis indicated a higher-than-expected probability of a critical anchor failing, which in a large enough flood event could fail the entire posttensioned anchorage system. In preparation for such an outcome, two contingency plans involving anchorage replacement and a steel exoskeleton wrapped around the trunnion girder with new anchors were developed and compared.

The Construction Owners Association of Alberta (COAA) and the Construction Industry Institute (CII), in collaboration with the University of Calgary, researched project performance improvement. The research investigated the usage of the COAA/CII benchmarking system in order to draw attention to the benefit of improved project performance in Alberta. A qualitative research methodology was used for investigating the usage of the system. Interviews, which contained open-ended questions, were conducted with industry practitioners. The results of the research showed that a lack of resources and a lack of an understanding of benchmarking are the major barriers to adopting the benchmarking system. The usage of the system will contribute to better project performance. The system has the potential to contribute to a reduction in cost and schedule overruns. It is concluded that the system can provide a guide for companies to improve project performance in Canada.