Practice Periodical on Structural Design and Construction

The main aim of this investigation was to study the flexural strength of simply supported rectangular RC hollow beams (with a longitudinal circular hole) subjected to gradually increased and symmetrically applied two-point loads. Each hollow beam had a 25-, 40-, or 50-mm-diameter hole, and the position of the center of the hole also varied from 45 to 180 mm from the top. The cross section of the beam, the amount of longitudinal steel, and the transverse steel of the beam were kept constant. The same M20 grade of concrete was adopted for all of the beams. The shear span-to-effective depth ratio (a_v/d) of 2.69 was kept constant. Theoretical equations are developed, or existing equations are modified, to determine the first cracking load and the ultimate load of the beams. The influence of the hole on the strength of the beams is studied by taking into account the area and position of the hole. To examine the validity of the developed theoretical equation, 12 hollow RC beams and one solid RC beam were cast and tested to failure. The behavior and flexural strength of these hollow beams were compared with that of a solid RC beam that had the same outer dimensions and steel reinforcements. The flexural mode of failure was observed in all hollow RC beams tested. A comparison of experimental results shows that the developed theoretical model satisfactorily predicts the first cracking load and the ultimate flexural strength of hollow RC beams.

The three most common nonlinear displacement-based methods were applied in the seismic design of two bridges in western Tennessee, and their results in terms of maximum seismic displacement demand and displacement ductility were compared. In addition, two different support-modeling configurations were evaluated. The results indicate that use of the simplified LRFD procedure results in a displacement demand higher than that of the other procedures. The support configuration with simplified seat-type abutments with rigid bent foundations provides results not significantly different than those achieved from the more detailed configuration with stub-wall abutment with flexible bent foundations, but it required fewer modeling efforts.

This work presents an investigation into the causes of collapse in scaffolds. The study was performed by identifying the prevalence of common scaffold design and construction attributes (such as those related to the geometry and construction of a scaffold or applied loads) during collapse and studying any correlations between these attributes and the number of scaffold collapses over several years. The data on scaffold collapse were gathered from those published by the Occupational Safety and Health Administration (OSHA). Using these data, the causes of collapse were classified into several categories, and scaffold attributes prevalent in collapse within each category were examined. This classification was further refined into two main categories of collapses resulting from (1) improper design or (2) construction errors. The comparison of failure data for these two categories determined that the improper design of scaffolds causes approximately 50% more collapses than construction errors.

Construction projects often suffer from cost overruns and time delays. Incentive/disincentive (I/D) provisions are contracting strategies that encourage stakeholders to complete a project with optimal cost and time. During the last decade, incentive mechanisms have gained momentum in numerous industries and are becoming increasingly adopted in building projects. While few studies have investigated the effect of incentives on the construction industry, mostly using qualitative research approaches, the current study adopted a quantitative approach to measure the performance impacts of cost-based incentives in the U.S. building construction industry. First, the paper summarizes the previous research on the topic, including the benefits and types of incentives. Second, a survey conducted to collect data from more than 30 U.S. building projects is discussed. Third, the statistical methods used to analyze the collected data and test the significance of observed differences in performance between the two data sets, projects with incentives and projects without incentives, are presented. The results show that cost-based incentives can reduce cost and schedule overruns by 5.3 and 8.4%, respectively. This paper contributes to the growing body of knowledge on incentives; it provides empirical findings about the impact of incentives on the cost and schedule overruns of building projects in the United States.

This paper provides a simplified formula for modeling the transition between material and structural failures in static and dynamic loading situations. For static situations, the transition equation allows for the calculation of the ultimate capacity between buckling structural failure and compression material failure modes. For dynamic situations, the transition equation allows for the calculation of a smoothed S-N curve between the constant amplitude fatigue limit, namely, the endurance limit, and the low-cycle, high-stress fatigue limit. The simplified formula is based on a quadratic solution that is curve fit to each failure mode and is verified with existing experimental data.

In this paper, a totally precast concrete counterfort retaining wall system is proposed for highway and bridge applications. This system provides several advantages over conventional methods, such as reduced construction time, cost, and environmental impacts. The system is composed of a precast counterfort wall that is connected to a base slab through headed anchors. The components are cast offsite and transported to the construction site for final assembly. The proposed system requires a unique method of construction. Accordingly, this paper details the fabrication and construction procedures required for the proposed system to accelerate the on-site erection process. In the use of this system, the general guidelines for the fabrication and construction of the totally precast counterfort retaining wall system are presented to the contractors. The system’s components can be fully assembled and set in place in approximately 2 hours.

As of 2013, the Federal Highway Administration (FHWA) estimated that one-third of the total bridge deck area in the United States was structurally deficient. Providing for the effective management and repair of these decks requires transportation agencies to have access to the best available information about structural conditions. Bridge deck inspection has long relied on sounding techniques, such as tapping and chain drag, which can be time intensive and may not provide enough information for accurate repair estimating. Nondestructive evaluation (NDE) techniques may provide faster and more accurate data collection, but their value needs to be proven to transportation agencies and bridge owners. This paper describes a case study considering the two NDE techniques available for inspecting bridge decks with asphalt overlay: ground-penetrating radar (GPR) and infrared (IR) thermography. NDE scanning results and as-built repair data for four bridge decks were made available to the research team. Comparison of the NDE findings to the actual repaired areas demonstrates the limitations and advantages of putting NDE deck scans into routine bridge inspection practice. Inferences made from the comparison are used to suggest improvements to NDE practices to take fuller advantage of the available technology. The main recommendation is to include an additional data processing step for improving data interpretation.

Seismic shutoff devices are expected to automatically stop the flow of hazardous gases and liquids through distribution systems that may be damaged by earthquakes. There is some uncertainty in the actuation of these devices; they may actuate when not needed and they may not actuate when needed. Therefore, these devices can only reduce, and not eliminate, the risk of hazardous leaks. It is shown in this paper that shutoff devices can be deployed to meet specific performance goals in seismic design. A cost-benefit analysis is conducted to show that devices are most effective in reducing the risk to weak systems in highly seismic areas. The uncertainty in actuation diminishes the effectiveness of these devices.

Practicing engineers generally obtain stiffness and damping coefficients for dynamic design of pile foundations from design charts. The design charts require multiple interpolations and produce approximate frequency-independent coefficients. Explicit expressions consistent with the underlying theory for the vertical vibration of single piles are presented in this technical note. These expressions are easily implemented in a computer program, such as a spreadsheet, for design use. The proposed method preserves the frequency-dependent nature of the dynamic coefficients and enables one to account for the true condition of the pile tip. The effectiveness of the proposed method is illustrated with numerous examples.