Practice Periodical on Structural Design and Construction

In performing alternative path analyses for checking the potential of a structure to progressive collapse, most designers often choose static procedures, which tend to be simpler and less labor demanding. As progressive collapse is a dynamic and nonlinear event, the load cases for the static procedures require the use of factors to account for inertial and nonlinear effects. A number of inconsistencies have been identified in the way the existing guidelines applied dynamic and nonlinear load factors to their static approaches. As part of an existing effort to update the existing guidelines, this study looked into the behavior of a variety of reinforced-concrete and steel moment-frame buildings to investigate the magnitude and variation of the dynamic and nonlinear load increase factors. The study concluded that the factors in the existing guidelines tend to yield overly conservative results, which often translate into expensive designs and retrofits. This study identified new load increase factors and proposes a new approach to utilize these factors when performing alternative path analyses for progressive collapse.

Recent years have seen a vast change in measurement technology. Data that were once extremely difficult and possibly dangerous to collect can now be collected and processed using only a digital camera and off-the-shelf software. Currently, digital close-range photogrammetry has made it possible to efficiently model a variety of structures in a budget-friendly manner. In this paper, a range of different types of structures were modeled. The viability of using this type of measurement is studied for different structure types, and the feasibility of using this method in conjunction with or as a replacement of other means is discussed.

The use of traditional urban infrastructure construction techniques, particularly open-cut construction, is being used less and less because of the benefits offered by trenchless techniques. These techniques typically reduce the disruption and impact on both the environment (i.e., reduced greenhouse-gas emissions) and society (i.e., reduced traffic and pedestrian delays attributable to road and sidewalk closures). In Colombia, owners such as Empresas Públicas de Medellín E.S.P. and the Colombian Institute for Subterranean Infrastructure Technologies and Techniques have promoted the use of these technologies in urban areas. The primary techniques used in Colombia for installing and rehabilitating urban infrastructure are pipe bursting, horizontal directional drilling, cured-in-place pipe, and microtunneling. Automated decision support tools are available in Colombia to assist designers in selecting technically viable techniques. This paper describes the trenchless techniques used in Colombia, a brief description of a decision support system available for selecting construction methods, and discusses four applications for installing and/or rehabilitating underground utilities through case studies of projects in Colombia.

When a structural element fails, it is often necessary to determine whether the element was properly designed, fabricated, constructed, and maintained. Among the many things that such a determination requires is an appropriate benchmark strength; i.e., a capacity that can be compared with the loading that caused the failure in order to determine whether the element met the appropriate expectations. Establishing a rational benchmark is complicated by the fact that common industry design, fabrication, and construction methods can result in substantial and highly variable deviations from the actual strengths of structural elements relative to the corresponding nominal values. This paper uses first-order reliability methods—similar to those used to develop the current AISC LRFD steel design provisions—and other methods to arrive at a rational definition of how strong a particular element needs to be in order for it to be considered strong enough.