Editor’s Note

Papers appearing in this issue of the Journal are selected from the following themes: metal structures, reinforced concrete structures, wood structures, dynamic effects, and wind effects. The issue concludes with two technical notes—one dealing with the application of active control techniques in optimal design of passive devices and the second concerning the behavior of OSB-sheathed wood shear panels with and without openings.

A two-part paper by Vian et al. examines the behavior of “Special Perforated Steel Plate Shear Walls with Reduced Beam Section Anchor Beams.” This paper presents results of an experimental investigation of specially detailed ductile perforated steel plate shear walls (SPSWs) designed to accommodate utility passage, and having anchor beams with Reduced Beam Sections connections. In the first part, findings from an experimental study on single-story, single-bay specially detailed ductile perforated steel plate shear wall (SPSW) frames are presented. The tested specimens included low yield strength (LYS) steel infill panels and also incorporated allowances for penetration of the panel by utilities. Though all specimens resisted the imposed input history of increasing displacements to a minimum drift of 3%, the perforated panel reduced the elastic stiffness and overall strength of the specimen by 15% as compared with the solid panel specimen. In the follow-on paper, finite element (FE) models of full SPSWs and sub-element strips are developed using ABAQUS to facilitate a comparison with experimental results and to investigate the influence of localized distribution of panel stress and strain between perforations. Based on the analytical and experimental results, recommendations for the design of these special detailed perforated SPSWs are proposed.

In “Direct Strength Design of Cold-Formed Purlins,” Pham and Hancock investigate the effects of combined bending and shear that occurs in a continuous purlin system, which is presently not considered in the newly developed Direct Strength Method of Design (DSM) of both the Australian/New Zealand Standard and the North American Specification for the Design of Cold-Formed Steel Structural Members. Findings from eight different test series on purlin sheeting systems with single, double, and triple spans and both uplift and downwards load cases as well as screw and concealed sheeting carried out over a $10\text{-}\text{year}$ period at the University of Sydney are used to propose two methods for use in the Direct Strength Method. The first proposes to use the lesser of the local buckling and distortional buckling section strengths in the combined bending and shear interaction equation, while the second recommends using only the local buckling section strength in the interaction equation. However, the writers suggest that the latter approach is an acceptable method for safe design even though it ignores the distortional buckling strength.

“Single-Span Deep Beams Subjected to Unsymmetrical Loads” by Zhang et al. investigates the effects of unsymmetrical loadings on the strength and behavior of simply supported deep beams. Test results from an experimental program consisting of 14 specimens are discussed with respect to the effects of load inequality (LI) and load asymmetry (LA). The ACI 318-05 Strut-and-Tie method is found to slightly overestimate the beam shear capacity. The writers propose a direct strut-and-tie method for predicting the failure loads of non-symmetrically-loaded deep beams. A load parameter $\Pi$ is introduced such that the proposed STM can model both the effects of LI and LA. It is shown that the proposed STM is a generalized form that embodies the special cases of single-point and two-equal-point symmetric loading conditions.

Wu and Wang develop a “Unified Strength Model for Square and Circular Concrete Columns Confined by External Jacket.” Based on extensive experimental testing on FRP-confined concrete columns that have a continuous variation of the corner radius, $\rho$ , from 0 to 1, a rational procedure is proposed for developing a unified strength model for FRP-confined concrete columns with an arbitrary corner radius. A comprehensive database consisting of nearly all available experimental results from the literature is compiled to evaluate the unified model. It is shown that the proposed procedure is applicable to concrete columns confined not only by FRP materials, but also other materials such as steel plates.

Pang et al. examine the seismic performance of typical one- and two-story wood frame structures in “Seismic Fragility Analysis and Retrofit of Conventional Residential Wood-Frame Structures in the Central United States.” Six structures with two foundation types are considered and conditional limit state probabilities (fragilities) are evaluated considering three possible failure mechanisms: excessive inter-story drift, wall uplift, and sill plate splitting. The assessment indicates that seismic damage to wood frame structures in the CEUS under earthquakes of moderate intensity is unlikely to lead to loss of life, but may result in significant financial losses. An evaluation of two possible retrofit strategies illustrates how the expected seismic performance of the CEUS structures can be improved by adding more anchor bolts and perimeter sheathing nails to the shear walls.

“Fully Reversed Cyclic Loading of Shear Walls Fastened with Engineered Nails” by Fonseca et al. presents findings from an experimental program in which fifteen shear walls, each constructed with either conventional or engineered sheathing nails, were tested under fully reversed cyclic loads. Four types of conventional nails and three types of engineered nails were used. Walls with one type of engineered nails exhibited the highest ultimate load capacity, whereas the stiffest walls were those with certain type of conventional nails. The displacement capacities of walls with engineered nails that exhibited the largest capacity were generally slightly less than that of walls with conventional nails, though walls constructed with one type of conventional nails had the lowest displacement capacity.

Common equivalent linear models are reviewed by Wang in “Intrinsic Damping: Modeling Techniques for Engineering Systems,” and their implementations for modeling energy dissipation on system and material scales are compared using simple, representative examples. It is shown that several independent methodologies result in approximately the same predicted responses for systems with uniform dissipative characteristics if certain assumptions are made regarding the frequency dependence of intrinsic damping. However, these assumptions result in divergences of predicted responses when extended to composite systems with nonuniform dissipative characteristics. Since no analytical or validated numerical solutions exist for systems with nonuniform dissipative characteristics, the writer suggests that further research is essential to generate a robust means for capturing energy dissipation across all levels of complexity in engineering systems.

The results of nine drop weight slab strip tests are reported by Habel and Gauvreau in “Behavior of Reinforced and Posttensioned Concrete Members with a UHPFRC Overlay under Impact Loading.” The primary parameters investigated in the study were the reinforcement configuration of the concrete substrate, the addition of reinforcing bars in the UHPFRC layer, and the static system. A three-point bending and a cantilever system were used in the drop weight tests to induce flexural compression or tension in the upper UHPFRC layer. It is shown that the addition of the UHPFRC overlay improved the structural response of the slab by preventing crushing or spalling at the impact location, minimizing crack widths in the substrate, and lowering member deflections.

A summary of updates made to the hurricane simulation model that forms the basis of the hurricane wind speeds given in ASCE 7 is presented by Vickery et al. in “U.S. Hurricane Wind Speed Risk and Uncertainty.” New data since the development of the model used for the ASCE 7-98 wind speeds have resulted in an improved hurricane wind field model. Estimates of uncertainties in predicted wind speeds are obtained by propagating the uncertainties in key model inputs through to the wind speed prediction stage. The two parameters controlling the overall wind speed prediction uncertainty are the modeling of the Holland B parameter and central pressure. The inclusion of a wind field modeling error term derived from comparisons of 245 modeled and measured wind speeds results in an upwards shift of the wind speed versus return period curve. It is found that the new hurricane hazard model predicts lower hurricane wind speeds than those given in ASCE 7 even though the overall rate of intense storms (as defined by central pressure) produced by the model is higher compared to the hurricane simulation model used to develop the ASCE 7-98 wind speeds.

The issue of whether active control approaches can be adapted to optimal design of passive controllers in linear structures is addressed in the technical note “Quantitative Comparison of Optimization Approaches for the Design of Supplemental Damping in Earthquake Engineering Practice” by Levy and Lavan. Since the objective function is a time integral of a functional of both response quantities and control forces, it is shown that the minimization of such a smeared quantity cannot lead to truly optimal added damper schemes. Next, Doudak et al. investigate the “Capacities of OSB-Sheathed Light-Frame Shear-Wall Panels with or without Perforations.” Results of experimental data are used to examine how openings for doors and windows influence the in-plane shear stiffness and load capacity of light-frame wall panels sheathed with Oriented Strand-Board. Test results indicate that there is a complex interplay present between choices in the specification of construction materials and details, and that wall panels in racking tests are very sensitive to even minor alterations in their boundary conditions. A key finding is that for walls without supplementary hold-down hardware, wall perforations have a disproportionate influence on wall panels.