Editor’s Note

The editor’s note includes a brief description of the content of the papers and articles included in this issue of the Practice Periodical on Structural Design and Construction.

The first paper deals with the effects of earthquakes on light-frame wood buildings. Experimental studies were conducted to test isolated wood shearwall assemblies and isolated building corner assemblies consisting of a shearwall and a short transverse wall. Both types of assemblies were tested with and without drywall by subjecting them to a series of simulated earthquakes of increasing intensity. The drywall reduced the peak drift of the isolated shearwall by 30% and that of the corner building assemblies by over 50%. Corner assemblies without drywall were severely damaged by the repetitive simulated earthquakes.

The second paper is an inquiry into the fatigue behavior of segmental, precast concrete bridges. An experimental study was conducted on a single-cell scale model of a precast posttensioned segmental box bridge system. That was subjected to cyclic loading and temperature changes. The test bridge was a 1:3.5 scale model of the Long Key Bridge in the Florida Keys. The performance of the bridge model was evaluated in terms of deflections, strains in the concrete and strain across the joints, and cracking behavior of joints between the segments. Results indicated that the behavior of joints between the segments under static and fatigue loadings was satisfactory up to two million cycles. No joint openings or cracks were observed at the joints under loading.

The third paper deals with temporary structures such as scaffolding and facilities that are used during construction of new facilities or during reconstruction or repair of buildings, bridges, and other structures. Such temporary structures may be designed to resist both seismic and wind loads; however, these loads may be reduced to a load level that is proportional to the intended service life of the structure. Although such a “reduced” design load may be reasonable for a structure that is used only once, this however may not be reasonable if the structure is used for a longer time period than was originally intended. This paper focuses on this issue and suggests a modified risk level to be employed in making a decision on whether to allow the structure to be used longer than its intended use period.

The fourth paper deals with the design of lightweight wood roof truss assemblies. The objective of the study reported here is to develop an “improved and practical” design method that can be used by the industry and that is capable of considering “systems effects” that are not accounted for by conventional design procedures. The authors made use of a commercially available structural analysis program to model and study three-dimensional roof truss assemblies and to evaluate “systems effects” not considered in conventional design.

The fifth paper deals with an overview of the earthquake-resisting system design and retrofit strategy for highway bridges in the state of Illinois. The primary objective of this strategy is to prevent span loss. This is to be achieved through three levels of seismic structural redundancy that allow for certain levels of damage at planned locations in bridges. Such controlled damage at strategic locations on a bridge would allow for mitigation of seismic energy. Sacrificial connections between the superstructure and substructure, conservative beam span lengths, and plastic hinging at planned locations are primary areas of focus for three levels of seismic structural redundancy in this strategy.

This issue also contains articles in the Structural Design and Construction Forums. The article in the Structural Design Forum deals with the strength of structural elements when subjected to airblast. Its purpose is to provide some very basic information on a loading condition that is not generally considered in engineering education. In the post-9/11 climate, such information may be of some interest to practicing engineers and is provided here for the purpose of discussion.

The article in the Construction Forum deals with scaffolding as related to safety, design, and construction issues. The article is motivated by an accident that occurred in Chicago in March 2002 in which three individuals were killed when a suspended scaffold fell from the 42nd floor of a building onto their vehicle during high winds. This article briefly compares the Chicago Municipal Code related to “scaffoldings” before and after this accident and is provided also for the purpose of generating discussion.