Practice Periodical on Structural Design and Construction

Many existing bridge structures experience much more significant loads and load cycles than were anticipated when the bridges were originally designed. An effective way to increase the load capacity and fatigue resistance of bridge structures with steel girders and a noncomposite concrete deck is to retrofit the structure with shear connectors to create a composite girder–deck structure. This article presents a state-of-the-art study of postinstalled shear connectors in general and coiled spring connectors in particular. The strengthening method is described, together with experiences from real bridge strengthening projects and a study of load capacity and structural behavior.

A capital investment of about USD 1.3 trillion is needed over the next 25 years to repair or replace the drinking water main breaks that occur each year in the United States. The use of two alternative delivery methods—design-build (DB) and construction manager-at-risk (CMAR)—for buildings, highways, and water and wastewater infrastructures are increasing due to schedule advantages, cost savings, and use of innovation in projects as opposed to the traditional design-bid-build approach. This study compares and analyzes the differences in the perceptions of DB and CMAR users regarding the various benefits of DB and CMAR for water and wastewater projects. The respondents of this survey were utility managers, project staff, and policy makers who have worked on DB and CMAR water and wastewater projects. Results showed no significant differences in the satisfaction level between these two methods regarding the benefits. However, CMAR users ranked “quality” significantly higher than DB users. In addition, a significantly higher number of DB users experienced a cost advantage in their projects when compared with CMAR users.

The recent rise in high-profile vehicular attacks has exposed vulnerabilities in design considerations for urban spaces used by pedestrians. These vulnerabilities need to be addressed by engineers when designing the spaces, but standards must be developed to aid in the design. Changes in zoning can allow some areas to be hardened based on cultural, political, and other criteria for how the space is and can be used by pedestrians. This study examined recent high-profile vehicular attacks, reviewed existing site design standards for security, researched security considerations for special events, and developed risk-mitigation proposals. This article proposes the development of mandatory government standards for the site design of soft targets, municipal zoning management focused on pedestrian-centered areas, and more considerations to be made when planning special events to mitigate the threat of a vehicular attack.

Cross-laminated timber (CLT), a new generation of engineered wood product developed initially in Europe, has been gaining popularity in residential and industrial applications in several countries because of the many advantages it offers. Being an orthotropic material, CLT behavior is challenging to predict in various applications, thus requiring caution from engineers and researchers. This study presents the analysis and design procedure for CLT crane mats, mainly used to provide a stable roadbed for heavy vehicles used in the oil and gas industry. Three-dimensional (3D) nonlinear finite-element (FE) models, using ANSYS, have been created, analyzed, and compared with experimental work previously performed by the authors. The orthotropic elastic and damage models have been used to model CLT linearly and nonlinearly, respectively. After the effectiveness of the model was determined, a comparison was carried out between the behavior of traditional wood mats connected by steel rods and various configurations of CLT mats. This comparison showed that the unique orientation of layers gives CLT more strength compared to traditional wood mats, which are strong only in the direction of the grain. A CLT design procedure was developed according to previously published guidelines for crane mats supported by soft soil and the effective section properties of the CLT. Recommendations were made for the design procedure for CLT mats that also highlight the limitations of previous published guidelines.

The collapse of structures due to massive seismic events is usually observed around the world. It is very important to rescue people who are trapped inside the collapsed RC structures by a big earthquake within 72 h after the earthquake has occurred. Thus, an electrical discharge impulse crushing system (EDICS) may be very effective in the rapid dismantling of collapsed RC structures. As a pioneering work, this study aims at developing a novel technique in controlling the growth direction of a crack formed in concrete by the EDICS. The effectiveness of empty holes created around a charging hole for controlling the crack growth direction is investigated through EDICS testing of concrete plate specimens. As a result, the relationship between the empty hole diameter and the center-to-center distance between the charging hole and empty hole must be satisfied with one particular equation. Finally, the analytical results of LS-DYNA are in good agreement with the experimental observations. This study as a whole would provide a platform to the disaster mitigation team to strategize the rescue operation in an effective and efficient manner.

Bridge expansion joints are a particularly troublesome component of bridges, and many DOTs are seeking maintenance solutions for deteriorating expansion joints. Bridge expansion joints create a break in the structural continuity of a bridge, allowing clogging gravels and corroding chlorides to enter. To prevent deterioration of other bridge elements, the joints must be cleaned regularly and replaced promptly after failure. Unfortunately, limited time and resources hinder most DOTs from properly maintaining expansion joints, which eventually leads to deterioration of bridge elements. To reduce maintenance problems, some DOTs have started to move away from the practice of repeatedly replacing the joints upon failure in favor of retrofitting bridges to remove joints altogether. Life cycle cost analysis (LCCA) provides a formal way to compare alternative approaches for dealing with bridge expansion joints. This paper presents an LCCA for existing bridge expansion joint alternatives, including the practices of routine joint replacement and removal of joints. Three different cost scenarios are considered, including the consequences of leaking expansion joints. All scenarios indicate that the removal of all bridge expansion joints in favor of a continuous bridge deck is a cost-effective maintenance solution.

Precast, prestressed bent caps are an attractive design option because they permit accelerated bridge construction and can extend the service life of bridges by reducing or eliminating the service-level cracking observed in RC bent caps. A design procedure is recommended for the flexural design of pretensioned bent caps in which the amount of prestressing is selected to ensure zero tension at service, with service- and strength-limit states serving as checks on the design. Recommendations include how to account for openings for connections that may influence the bent cap performance. Using the recommended flexural design procedure and AASHTO shear design provisions, pretensioned bent caps were designed for a suite of multicolumn bridges. The flexural design procedure is shown to be efficient for the design of most bridges, and many bent caps are expected to have only minor cracking, if any, at ultimate demands. The minimum area of transverse reinforcement was found to govern most bridge designs, leading to recommendations to use the general, noniterative sectional shear design method. The resulting designs lead to recommendations for how designers and contractors can use precast, pretensioned bent caps not only to enable accelerated construction and extend bridge service life but also to increase design and construction efficiency.

The cost optimization of the internal composite floor bays with castellated steel beams was studied using a genetic algorithm. A computed flowchart, input variables, constraints, and output variables are presented. The cost optimal function was defined using a price list of the different floor components. The accuracy of the model was validated by comparison with two literature examples. Comparative simulations were conducted to explore the effect of various influential parameters in optimal design, and the number of floor divisions, dimensions of hexagonal openings, and number of web openings were considered. The simulation results show that there were no significant effects on the composite bay cost due to the changes in the number of floor divisions or web openings. Web opening limitations were presented to minimize the cut length. In addition, design guidelines for opening dimensions to reduce web buckling were discussed.

Sustainable building projects gained momentum in the last decade, and the trend continues. This article explores the factors affecting the sustainable building delivery process. It highlights the differentiating aspects of sustainable building projects from conventional projects in regard to project phases and makes recommendations about the timing of services, such as value engineering, constructability analysis, technology integration, and construction manager and specialty subcontractors’ involvement. The survey questionnaire content was created based on the literature review findings. It was conducted with 17 executive-level managers of major green builders in the United States. The results indicate that design-build is the most preferred method, preconstruction services require more time, iterative processes are used, and the early involvement of project participants is critical in sustainable building delivery. Team integration and the chemistry among team members significantly contribute to successful outcomes. The utilization of building information modeling is key in providing effectiveness from the initial design to the postconstruction phase. The study is of relevance to industry practitioners who want to capitalize more on sustainable projects, and it is of relevance to researchers, too, because it provides input regarding the sustainable practices of top green contractors.

A comparison is made between the three conventional methods used for accelerated bridge construction (ABC) of railroad bridges in Iran: single-piece deck installation by heavy cranes, multisegment deck installation by cranes, and single-piece deck installation by the so-called roll-in or sliding method. Both the safety of the construction and the serviceability of the railway line during the construction process are the main factors influencing the appropriate alternatives. Four railroad bridge construction case studies are demonstrated and compared here. Based on the individual situations, it is shown that the use of the roll-in method, in comparison with installation by crane, can reduce the installation costs significantly, eliminate the fatigue-prone details of the steel connectors, and eliminate the time for concrete casting in conventional multisegment deck installations.

There have been numerous publications on unreinforced masonry construction in the literature; however, there is a lack of publications on the condition assessment of existing unreinforced masonry façades for disturbances due to nearby subway construction. To fill this gap, this paper presents a study in which a 5-story historical building with unreinforced masonry façade experiences inward and outward deformations perpendicular to the plane of wall due to nearby subway construction. The performance of the unreinforced masonry façade is examined under wind load combinations. For this, a finite-element (FE) model is built in ANSYS software to conduct a stress analysis of the brick façade. The results revealed that the tensile stresses exceeded the tensile stress limit at several locations; therefore, a structural remediation is required. A structural retrofit is proposed to tie the façade wall to the floor diaphragms with steel anchor rods at specific stories. Another FE model is built to represent the remedies proposed for stabilizing the façade wall. The results show that all stresses are within the limits, indicating that the structural solution for the remediation is appropriate. As a result of this study, the proposed remediation was implemented at the building, and the structure has been in good structural condition without any complaints, even after the subway construction was completed and the subway line was in operation.

Vibrations serviceability of building floors has been a growing concern over the years. For steel-framed systems, vibrations serviceability checks often govern the structural design. When the floor is carrying vibration-sensitive equipment, vibrations serviceability evaluation is more critical because the serviceability on the floor involves the use of expensive equipment generally related to human health (patient rooms, operating rooms, medical laboratories, etc.) This article summarizes a study in which a new (replacement) magnetic resonance imaging (MRI) unit with a weight of 8.6 t (19,000 lb) was to replace a heavier MRI unit weighing 37.2 t (82,000 lb) on an elevated floor of a medical facility. Although the dynamic characteristics of the floor would change with this drastic load difference on the bay, the vibration response of the floor for nearby footfall excitations was also expected to change. This brought up the question of whether the footfall-induced excitations would pass the maximum acceleration limit set by the manufacturer of the replacement MRI unit. The authors were provided with in situ vibration measurements collected when the old MRI unit was in place and were asked to decide if the footfall-induced excitations around the replacement unit would exceed its manufacturer criteria. Sparse in situ vibration measurements of the old MRI configuration were used to calibrate a detailed finite-element model that was later used to predict the footfall response for the replacement MRI unit configuration. The predicted accelerations were then compared with the manufacturer’s limiting accelerations for the replacement MRI unit. It was determined that the accelerations estimated for the replacement unit were not more than the manufacturer’s limiting criteria.

This paper presents a finite-element (FE) study conducted to investigate the deflections of newly constructed cantilevered slabs built for a medical facility expansion. From the beginning of the construction stage, the deflections of the newly built cantilevers caused disputes among the owner, contractor, and the structural engineer of record. The study presented here was performed to understand whether the cantilevers were designed and built to conform to the governing codes. The cantilever deflections at three levels and their relative displacements were studied in detail for comparison with the measured values at the job site and code limitations. The mainstream structural engineering software programs predominantly used in structural engineering offices are generally run to identify the most critical load combinations, critical forces, moments, and deflections of structural members; however, a deflection study such as the one described here requires an extensive FE model created with comprehensive software like ANSYS to investigate the sequential loading of cantilever deflections. In ANSYS, the reinforced concrete behavior can be simulated with SOLID65 elements, which provide an excellent fit for representing the true stress–strain diagram of reinforced concrete. The FE modeling with ANSYS SOLID65 elements for flat slab cantilever deflections have not been discussed in detail in a technical publication before: This study fills that gap. The study not only covers the detailed FE modeling with SOLID65 elements, but it also compares the results with the measured deflections and code requirements. In addition, the study provides recommendations for avoiding excessive deflections in cantilevered reinforced concrete construction.

Parking garages are unique building structures in that they are often open to the environment and exposed to deicing chemicals, making them susceptible to deterioration, particularly through the corrosion of reinforcing steel. The exposures parking garages face make it important to design them specifically for durability and to consider long-term costs and performance in their design. Life-365 is a software tool developed to aid in the service life–based design of reinforced concrete structures and to calculate the costs of ownership over the life span of the structure. This study was conducted to investigate the effects of different protection strategies on service life and life cycle cost (LCC) for a concrete slab in a parking garage and to assess the utility of Life-365 in helping designers and owners of these structures most effectively manage and allocate the resources they have. The protection strategies investigated are decisions made at the design stage including increasing the concrete cover distance to the embedded steel, decreasing the w:cm ratio, using supplementary cementitious materials (SCMs) in the concrete mixture, using epoxy-coated steel, and using membranes or sealers on the concrete slab surface. Results show that using SCMs and increasing the concrete cover distance were the best in enhancing slab durability and reducing total costs at the end of the design life. The study also demonstrates that, while Life-365 is well suited to assisting in the initial design of reinforced concrete structures, it has very limited utility in planning and projecting the usefulness of preventive maintenance.