Practice Periodical on Structural Design and Construction

The presented research proposes and experimentally validates a novel energy-based training module aimed at rapidly improving hazard-recognition skills in civil, environmental, and architectural engineering (CEAE) students. The module is based on the established theory that every construction hazard is fundamentally related to the unwanted release of one or more energy sources. Eighty-four members of a CEAE undergraduate class were participants during a three-week experiment. Adopting a rigorous A-B experimental design and validated protocol to measure hazard recognition, the study found the module increased students’ hazard-recognition skills by 67.8% on average (p < 0.001), with a lasting effect over time, while a standard lecture based on Occupational Safety and Health Administration (OSHA) training was found to be not significantly effective. Qualitative feedback gathered in the form of textual learning logs corroborated the quantitative findings. The study findings suggest that OSHA training may be complemented with components of the proposed method to improve hazard-recognition levels.

Most reported project management studies to identify major factors in construction delay are based on self-administered questionnaire surveys of the views of project participants. A small number of studies are based on the records of actual construction projects. No study of major delay factors based on the analysis of extension of time of construction projects has been reported in the literature. A study on project management in public housing construction and delay factors based on extensions of time for 184 high-rise apartment blocks of the public housing agency in Singapore is reported herein. A comparison of major delay factors identified by this study with those identified in an earlier study is reported. Comparison is also made with studies for Hong Kong, South Korea, and Taiwan. Measures to improve the schedule performance of the development of public housing projects with respect to the delay factors identified are proposed in this paper.

Pile driving has usually been the most prevalent method of pile installation, although the ground vibrations generated by pile driving operations have a high damage potential for structures in the vicinity and are a major concern. Hence, the intention of this study is first to facilitate problems associated with the ground vibration issues and then to evaluate the allowable distance of different structures adjacent to an impact pile driving site to prevent structural damage based on the acceptable vibration levels of reliable standards and a report in terms of peak particle velocity (PPV). In this regard, the numerical simulation of a continuous impact pile driving process for a case study is executed from the ground surface using the ALE (arbitrary Lagrangian-Eulerian) adaptive mesh method rather than common discontinuous pile driving models. Based on the results, peak vertical velocity is the most appropriate approach for the determination of PPV and the investigation of the ground vibrations induced during construction activities. Furthermore, the most comprehensive standard is concluded to assess transient vibrations caused by construction activities. For practical applications, maximum peak allowable PPV using the standard resultant was presented to prevent structural damage to different structures.

Posttensioning is an effective construction method for structures with large spans, intensive loadings, and cost-efficiency considerations. The investigation developed a comprehensive understanding of how various reinforcement ratios and compressive strengths of concrete contribute to deflection of posttensioned two-way slabs. Furthermore, the numerical analysis compared the efficiency of various codes of practice to design the required reinforcement ratio in the presence of constant posttensioning tendons ratio and layout to provide the strength and deflection requirement. The interaction between the compressive strength–deflection and reinforcement ratio–deflection to find the optimum values of compressive strength and reinforcement ratio in a posttensioned two-way slab was also investigated. The finite-element model of a posttensioned 10 × 10 × 0.2-m (32.8 × 32.8 × 0.65-ft) two-way slab was analyzed and evaluated. The study confirmed the considerable effect of posttensioning to decrease the reinforcement ratio and deflection in a two-way slab. Also, a wide range of differences in design of a similar section of posttensioned concrete slab was observed by applying different codes of practice. The intensive effect of the concrete strength on the posttensioning design of slabs, especially in the lower ranges of compressive strength, was evident during the numerical analysis. Additionally, the reinforcement ratio shows a minor effect on the deflection of a posttensioned slab.

Reasonably simple yet accurate estimation of inelastic displacement demands on bridges during strong ground shaking is a critical step in the structural design process. Current code methods rely on the equal displacement rule at long periods, with ductility-dependent amplification factors applied at short periods. The purpose of this study is to evaluate the validity of these current methods for bridges subjected to ground motions of varying duration. Three methods are employed: inelastic response history analysis, the substitute structure method, and a recent ground motion prediction model from the literature. Each method confirms the strong dependence of inelastic displacement amplification upon various intensity measures of ground shaking, while current methods from bridge design specifications do not account for this dependence.

This article provides recommendations on how to evaluate existing passive anchorage systems for Tainter gates. A review of various types of passive anchorage systems is provided, along with a detailed example problem. The example problem provides an overview of passive anchorage behavior, finite-element modeling, codified guidance, corrosion rate, and results comparisons. The aim of the study was to develop a valuable reference platform for designers to use in evaluating aging infrastructure that outlines good-practice techniques and decision making.

The application of operational modal analysis using frequency domain decomposition revealed the operational behavior of a cantilever sign support structure in response to truck-induced wind gusts. The study identified the modes of vibration that contribute to the total deformation of the structure during service. The research involved experimentation of an on-site cantilever sign support structure under a controlled test regime of truck gusts. The study measured normal- and shear-strain deformations around the circumference of the post in proximity to the base-plate weld. The results indicated a multiple-degrees-of-freedom dynamic system with two equally contributing modes of vibration. The modes resembled torsional and flexural vibrations about the post. The resulting operational deflected shape had a distinctive beating vibration response due to the modal contributions. The truck fatigue loading provisions of the AASHTO supports specifications were overly conservative for the tested structure and truck type.

The main aim of this investigation was to study the behavior of simply supported rectangular RC beams with 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 center of 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. Theoretical equations were developed or existing equations were modified by taking into account the area and position of holes to determine the maximum deflection at precracking and postcracking stages of the RC hollow beams. To examine the validity of the developed theoretical equations, a total of 76 RC hollow beams and 10 RC solid beams were cast and tested up to failure. Also, the behavior of these hollow beams was compared with RC solid beams having the same outer dimensions and reinforcements. The behavior of all of these beams was studied by measuring deflections and observing crack patterns. The comparison shows that the developed theoretical model satisfactorily predicts the maximum deflection at pre- and postcracking stages of RC hollow beams.

Changes and modifications to existing equipment and structures are often required to meet the process industry’s environmental regulations. Creative constructability solutions help minimize shutdown periods that affect production and reduce revenue. It is essential to find engineering constructability solutions for such modifications during shutdown periods while keeping the facilities within regulatory compliance. The case studies presented in this paper include modifications to five different flares in an oil refinery by adding a new flare gas recovery (FGR) to reduce emissions. The case studies examine the challenges to and solutions for projects that involved an oil refinery with FGR modifications for five different flares. These modifications required the bottom portion of existing derricked flare stacks to be removed and replaced with new stack tie-in sections designed to reduce emissions. The objective was to determine a way to accommodate the new FGR tie-in installations without having to perform a total removal of the flare stacks. Among the challenges included checking the capacity of the existing structures to support the dead load of the flare stack as well as temporary wind loads, maneuvering new steel through existing structures and piping leading to irregular geometries, and using temporary steel plate mat foundations in lieu of concrete foundations due to geotechnical concerns and limited excavation clearances. The solutions include reinforcing the existing derrick structures, using hydraulic jacks to control deflection, adding new additional support structures down to grade, and adding a new temporary foundation, or a combination of these solutions. The solutions presented saved the refinery significant time and money in additional downtime in case flare removal would be required. To develop the solutions, three-dimensional laser scanning and structural modeling was used, and a unique deflection-controlled hydraulic jacking process was developed.