Editor’s Note

The leadoff group of papers in this issue of the Journal deals with topics on structural reliability assessment. The next primary theme is seismic effects. This is followed by a paper on a formulation for the analysis of pressurized fabric beams and a paper outlining a new optimization procedure. Three articles on metal and composite structures and one on wood structures wrap up the technical papers selected for this issue. The issue concludes with a technical note on measures of wind speeds for use in structural design.

A methodology for developing “Cost-Benefit Importance Vectors for Performance-Based Structural Engineering” is proposed by Riederer and Haukaas to identify which structural parameters are most cost-efficient to change, to improve the reliability of an underperforming design. The results illustrate the change in reliability per dollar spent of different parameters. A distinction is made between design and tolerance parameters to allow any possible improvement of reliability by allocating resources to reduce variability in select system parameters. In “Fourth-Moment Standardization for Structural Reliability Assessment” by Zhao and Lu, the reliability analysis without the exclusion of random variables having unknown distributions and the third-order polynomial normal transformation technique using the first four central moments are investigated, and an explicit fourth-moment standardized function is proposed. Numerical examples demonstrate that the method is reasonably accurate with minimum additional computational effort.

The optimal sequences of maintenances time and rehabilitation levels, by maximizing the expected net present benefit rate throughout the lifetime of the system, are the subject of Macke and Higuchi’s paper “Optimizing Maintenance Interventions for Deteriorating Structures Using Cost-Benefit Criteria.” Numerical examples demonstrate that the proposed approach permits optimization of maintenance interventions and determines optimal lifetimes and acceptable failure rates. Christopher Eamon outlines the development of a procedure to assess the “Reliability of Concrete Masonry Unit Walls Subjected to Explosive Loads.” Blast load and wall resistance models are developed based on experimental and analytical data, a sensitivity analysis is conducted to identify significant random variables, and reliability indices are estimated for two wall types and three design blast load levels.

The “Conceptual Seismic Design of Regular Frames Based on the Concept of Uniform Damage” is proposed by Park and Medina.Frame structures designed using the proposed approach are analytically demonstrated to exhibit a more uniform distribution of story ductility and story drift ratios compared to lateral load distributions based on current U.S. seismic code provisions. To improve demand prediction using pushover methods, Park, Eom, and Lee propose a “Factored Modal Combination for Evaluation of Earthquake Load Profiles.” Multiple story load profiles are predicted by combining the modal spectrum responses through certain modal combination factors which depend on the influence of each mode on the dynamic response. The method is verified using prototype buildings with and without vertical irregularity.

Dicleli and Mehta propose an “Efficient Energy Dissipating Steel Braced Frame (EEDBF) to Resist Seismic Loads.” The proposed frame combines the advantages of moment resisting frames (MRF) and chevron braced frames (CBF). Analytical studies carried out by the writers indicate that the energy dissipation capacity of EEDBF is comparable to that of MRF while drift demands is comparable to CBF for low to moderate ground shaking and lower than both MRF and CBF at higher ground motion intensity. Two large-scale specimens were designed and tested by Phan et al. to investigate “Near-Fault Ground Motion Effects on Reinforced Concrete Bridge Columns.” Both columns experienced significant residual displacements even under moderate motions. A framework for the evaluation of reinforced concrete (RC) bridge columns with respect to the control of residual displacements is proposed.

“Beam Finite-Element Analysis of Pressurized Fabric Tubes” using a virtual work formulation is presented by Davids et al. Work done by internal pressure due to deformation-induced volume changes, fabric wrinkling and shear deformations are considered in the formulation. The finite element model is shown to accurately predict experimentally observed response of pressurized fabric beams loaded in three- and four-point bending for a range of pressures. The simulations demonstrate that in addition to prestressing the fabric, the pressurized air also increases the beam capacity as the beam volume decreases due to deformation.

A procedure for “Design of Space Trusses Using Big Bang–Big Crunch (BB–BC) Optimization” is developed by Charles Camp for both discrete and continuous variable optimization. BB-BC optimization is a population-based heuristic search with the objective of minimizing the total weight or cost of the structure subjected to material and performance constraints. Low-weight design and performance comparisons between the BB–BC procedure and other classical and evolutionary optimization methods are presented for several benchmark problems.

Results from a test program on full-scale simply-supported beams with a central concentrated load and an effective lateral brace at mid-span is reported by Zirakian and Showkati in “Experiments on Distortional Buckling of I-Beams.” The experimental beam strengths are compared to the design strengths predicted by the American Institute of Steel Construction (AISC) and Australian specifications. It is found that both specifications generally provide non-conservative estimates in the inelastic range as the beam length decreases and the degree of inelasticity increases. “Finite- Element Analysis of a Composite Frame under Large Lateral Cyclic Loading” by Zhou, Mosalam, and Nakashima discusses the modeling details of the steel frame, the concrete slab and the interaction between the frame and slab. A composite frame previously tested by the writers is analyzed using the proposed model and good agreement between experiment and numerical simulation is obtained up to rotation amplitude of 0.04 radians. Zhou and Young present findings from an “Experimental Investigation of Cold-Formed High-Strength Stainless Steel Tubular Members Subjected to Combined Bending and Web Crippling.” The specimens were tested using the interior-one-flange loading condition specified in the American and Australian/New Zealand standards. It is shown that the strengths predicted by both codes are generally conservative.

The seismic behavior of a new type of wood wall system is reported by Varoglu et al. in “Midply Wood Shear Wall System: Performance in Dynamic Testing.” Steel rods are used at the end of midply wall in lieu of hold-down connectors to prevent brittle tension failure at the end studs. This study in conjunction with previous work on midply walls indicates the suitability of the system for seismic applications where improved shear resistance is essential.

The issue concludes with a technical note by Simiu, Vickery, and Kareem examining the “Relation between Saffir-Simpson Hurricane Scale Wind Speeds and Peak $3\text{-}\mathrm{s}$ Gust Speeds over Open Terrain.” Estimates of the ratio of peak $3\text{-}\mathrm{s}$ wind speeds at $10\mathrm{m}$ over terrain exposure to $1\text{-}\min$ speeds at $10\mathrm{m}$ above open water are provided. The ratio based on the ASCE-7 power law model is 1.03 while the logarithmic law model yields ratios varying from 1.03 to 1.12, depending upon the surface roughness assumptions for flow over open water.