Practice Periodical on Structural Design and Construction

In this paper, an analytical model for the design of axially loaded strengthened RC columns with steel angles and battens is presented. Cases of directly loaded and not directly loaded steel angles are considered. The model considers the contribution in confinement pressures caused by transverse battens and steel angles and the contribution in terms of the load-carrying capacity of steel angles subjected to axial force and the bending moment. An experimental investigation on the compressive behavior of eight short, confined, RC columns externally strengthened with steel angles and steel battens with various pitches was carried out, and has been utilized as support for the analytical model. The analytical results generated are compared with the experimental data available in the literature and with those obtained by using existing analytical models. The comparison shows the acceptable prediction of the experimental results in both cases of directly loaded and not directly loaded steel angles. Finally, some design rules given by recent codes for the design of this strengthening technique are discussed using the proposed model.

Approach slabs have been used by many state transportation agencies as a means to prevent settlement problems on embankments leading to a bridge. However, many problems have reduced the effectiveness and life of the approach slabs or required excessive maintenance. Although the primary cause of approach slab problems is largely geotechnical in nature, the structural design of the approach slab is important to ensure that it performs its functions to an acceptable level over its service life and that said service life is reasonably long. A review of the literature reveals some of the approach slab problems and their causes, current design features, conclusions regarding design and maintenance, and recommendations that have been made to improve performance and service life. In this study, both the published literature and standard drawings available from state agencies are reviewed. This paper contains the results of this review, focusing on the structural design and construction issues of the approach slab. Currently, design guides are not available, requiring practicing engineers and state departments of transportation to rely upon experience and frequent maintenance. It is recommended that such a document be compiled to begin the process of standardizing the design of bridge approach slabs.

Shear connections develop a moment under the rotational demand imposed to them by the supported beam. For single-angle, double-angle, and tab to tubular column shear connections, this moment can be obtained through the equations derived from appropriate plastic yield line mechanisms. The primary application for the moment equations in the design of a connection is that the obtained moment can be used to estimate the load demand on the bolts and/or welds of the connection. This paper illustrated the moment equation method through various examples. Compared with the current empirical approaches in connection design, the proposed equation method is versatile and insightful.

Content of this article was driven by forensic investigation of a failed pressurized concrete water holding structure. Forensic analysis of that particular structure, review of the original design documents, and review of some comments made during the litigation revealed a very disturbing design tendency: many design professionals tend to oversimplify the design approach. As a result, tank owners receive a deficient design, a problem frequently litigated in the Courts. Omissions in the tank design are costly and frequently irreversible. The following discussion is written with the intention of helping design professionals, contractors, and tank owners to better understand the issues linked to design and construction of successful, watertight water holding structures.

Contractors have responded to the growing pressure from owners to shorten project duration by employing a variety of crew-scheduling techniques. Unfortunately, only a limited knowledge base exists for determining the impact of different crew schedules on project performance in terms of cost, duration, productivity, and safety. Standard crew schedules include those that require crews to work 40 h per week, including five 8-h days, four 10-h days, or a second shift. Overtime schedules are also common, which require crews to work additional hours beyond the standard 40 h per week. These overtime schedules include five 9-h days, six 8-h days, or five 10-h days. In addition to the standard and overtime schedules, several other crew-scheduling techniques have been used successfully by contractors. This paper presents the results of a study on the impact of crew-scheduling techniques on overall project performance. The paper identifies the proper application and conditions for successful use of various crew-scheduling techniques and provides a comprehensive comparison that outlines a variety of crew-scheduling options, along with their impact on labor efficiency, project duration, worker safety, and project cost. Contractors can use the results to aid them in the selection of a scheduling technique to best meet the specific requirements of a project.

Worker safety and health continue to be a huge concern for the construction industry. Construction contractors are always looking for new ideas that will help improve their company’s safety performance. One such idea is the utilization of safety performance indicators as part of contractor safety programs. There is no guidance in the safety literature to the contractors on the most effective leading indicators. The purpose of the study was to evaluate selected leading indicators under real project conditions and develop recommendations for their use by construction contractors. Three types of leading indicators were selected and tested for the study: pretask plan (PTP) review, worker safe behavior observation (WSBO), and site safety audits. To evaluate the leading indicators under real project conditions, a large construction project was selected from the western United States. It was found that pretask plan review and worker safe behavior observation can be used by contractors as leading indicators as part of their safety program. A WSBO is a better leading indicator compared with a PTP review indicator. These two indicators can help construction companies to devise intervention methods that can fix any weakness identified before there is an injury or incident. The paper provides two guidance checklists for contractors interested in implementing a WSBO and PTP review leading indicator program.

The engineers of the ancient Inca Empire cleverly used the resources of nature efficiently. Because of their unique awareness of nature, they were able to build durable structures that have lasted for more than 500 years. The structures they created reveal an exacting observation of the forces of nature and a honed ability to work in cooperation with those forces. This summation of the Inca storehouse structures in relationship to nature demonstrates that the relationship between construction and nature is powerful and can be used in a positive manner. Modern engineers can create more sustainable structures if they devote careful attention to nature.

Over the last few years, there has been the realization that the current electrical grid needs to undergo major upgrades. The government, utility companies, and several other stakeholders have proposed modernizing the electrical grid to make it efficient to meet predicted power demands. This modernized grid is generally termed as the smart grid. In addition to the grid capacity and reliability issues, the current electrical grid requires upgrades to resolve major challenges including the network of independently owned components, old and outdated parts, wastage from inefficiency, a design that did not consider renewable energy, and susceptibility to attacks from hackers and terrorists. It is evident that the growth of a smart grid will require substantial development and installation efforts. These efforts will present opportunities to the construction industry, especially electrical contractors. For electrical contractors to take advantage of these opportunities, they need to be conversant with technologies associated with a smart grid and their installation and construction management–related aspects. This research explored smart grid technologies both in the market and in research and development and developed the installation and construction management aspects of these technologies. The work scopes associated with these technologies for the electrical construction industry were also explored.

Falls from roofs are a significant risk for both construction and maintenance workers. A roof anchor system is the common design solution to eliminate the falling hazard. This paper presents the findings of a case study to serve as a preliminary investigation of the financial impact and risk of roof fall protection solutions. The research began with the selection of a project that featured a roof anchor system and a parapet that does not meet Occupational Safety and Health Administration (OSHA) guardrail height requirements. The intent of the research was to compare the cost of design and installation of the roof anchors and parapet with that of two other design options on the same project: only a parapet that meets the OSHA guardrail requirements; and no anchors or parapet. Data used for the study were collected through interviews of project personnel and reviews of project documentation. The parapet system was found be an expensive, but safer, alternative compared with the roof anchor system. The roof anchor system creates more risk to worker safety because of the extensive amount of temporary fall protection measures required during construction. This requirement puts more workers at risk of injury during installation of temporary guardrails and while working near the leading edge. The roof anchor system indirectly affects worker productivity by at least 15% compared with the parapet system. Using this study as a starting point, more research is recommended that examines the costs and risks associated with various prevention through design (PtD) solutions. Such research will assist owners and designers in making informed decisions while choosing PtD solutions.