Editor’s Note

The August 2012 issue of the Practice Periodical on Structural Design and Construction contains seven relevant and practical articles: six technical papers and one case study.

The first paper in this issue is “Prefabricated Bridge Construction across Europe and America” by Hällmark et al. The paper presents the experience from both Europe and the United States in an effort to promote the use of accelerated bridge construction (ABC) and prefabricated bridge elements. Prefabricating certain bridge elements reduces the time spent at the construction site and the impacts on the road users and the surrounding community. In some instances, entire structures have been fabricated off-site under strict environmental and quality controls, then shipped to the site and erected in a matter of days rather than months. For construction-minded professionals, this paper presents a useful review of ABC techniques that can be beneficial in reducing the cost and inconvenience to the public.

The second paper, “Configuration Optimization of Drilled Shafts Supporting Bridge Structures: Three Case Studies” by Robinson et al., discusses the common approach used to estimate the point of fixity for piles. Work in this study summarizes a method to determine the cantilever’s equivalent length of the drilled shaft foundation supporting a bridge. Results from an equivalent frame model are compared with those for bents modeled using the finite-element method and nonlinear soil models for three bridges in North Carolina. The study presents the results of the optimization of the support system by reducing the number or size of the shafts, while maintaining acceptable levels of safety. The optimization method presented in this paper will be useful to design engineers.

The third paper is “Seismic Retrofitting for Chord Reinforcement for Unreinforced Masonry Historic Buildings with Flexible Diaphragms” by Hsiao and Tezcan. This paper discusses wood-diaphragm-to-masonry-wall connections in unreinforced masonry (URM) buildings. Recent strengthening techniques for the connections between the URM walls and the flexible diaphragms concentrate only on the installation of wall anchorages for out-of-plane tension forces and shear bolts for in-plane shear forces. Strengthened chord elements, however, are also essential parts of URM buildings to resist earthquakes. This paper proposes seismic rehabilitation techniques where steel angles are used as chord reinforcement. A practical design example is presented in which chord axial forces caused by in-plane diaphragm deflections and chord shear flows caused by transverse seismic forces are computed. This paper will be useful to engineers designing buildings in earthquake zones.

The strong column–weak beam philosophy of the current design concept is discussed in “Prediction of Inelastic Mechanisms Leading to Seismic Failure of Interior Reinforced Concrete Beam–Column Connections” by Nilanjan and Pijush. The paper presents two alternative easy-to-use probabilistic methodologies, which can be used to determine the occurrence of inelastic mechanisms leading to failure. The relevance vector machine method was utilized to develop one model; the other model developed was the binomial logistic regression. A comparative evaluation of these two models has been presented. According to the evaluation, both methods show good predictive efficiency and can be utilized by engineers or researchers to obtain a preliminary probabilistic estimate of inelastic mechanisms leading to the failure of interior reinforced concrete beam connections.

“Accounting for Architectural Demands and Construction Phase in Structural Design” by Branco et al. is the fifth paper in this issue. This paper presents the analyses of a nontypical three-story building in Palmela, near Lisbon, Portugal. The building’s first floor façade was designed in a setback of the second floor. A Vierendeel girder was designed between the second and third floor slabs, and nonlinear analyses were conducted. Also, to account for the effect of creep in the construction phase, a nonlinear analysis was performed. The second-order effect on the vertical elements was accounted for through nonlinear analysis. The nonlinear analyses resulted in a more slender and cost-effective design compared to results obtained from traditional methods

In “Considerations for Design of Rafters in Timber Buildings,” Schmidt and Miller discuss roof rafters in timber buildings and their various methods of supports used by designers to achieve the various objectives. A detailed examination of seven common rafter configurations with varying support conditions is presented. The results of detailed structural analyses and evaluations of the impacts on roof system performance are discussed. The paper will be a valuable tool for design engineers to weigh the relative advantages and disadvantages of their selections.

Lan and Daigle present the case study “Verification of the Strength of the Anchor Point of Fall-Arresting and Positioning Systems for Reinforcing Steel Erectors,” that discusses fall protection in the construction of walls of great dimensions. The reinforcing steel erector has to climb on the reinforcement bars to anchor and gain a firm position to complete tasks and must be protected against falls. Two problems are identified: (1) the selection of a harness, positioning, and fall-arrest equipment, and (2) an anchor point sufficiently strong for the positioning and the personal fall-arrest systems. This paper describes the dynamic fall tests that have been carried out to verify the strength of tied reinforcement used as an anchor point for the fall-arresting and positioning systems of reinforcing steel erectors.

The editorial board thanks the authors of this issue’s papers, and welcomes and encourages readers to submit questions, discussions, and/or comments on the topics presented. Questions, discussions, and/or comments should be submitted as stipulated in the General Information section, which can be found at the front of this periodical.