Editor’s Note

Balling et al. propose a procedure for the “Design of Buckling-Restrained Braced Frames Using Nonlinear Time History Analysis and Optimization.” Results from the procedure are compared to those from the commonly used equivalent lateral force procedure. Results are used to develop design curves and formulas for rapid determination of cross-sectional areas for buckling-restrained braces in each story. It is shown that the optimum variation of area from story to story is nearly linear for most cases studied—a finding that is not predicted by the equivalent lateral force procedure.

A damage avoidance design (DAD) methodology that requires special armoring of the joints and eliminates the formation of plastic hinges is investigated by Solberg et al. in “Performance of a Damage-Protected Highway Bridge Pier Subjected to Bidirectional Earthquake Attack.” A DAD-based pier is designed to rock on steel-steel armored interfaces, and the theoretical performance of the DAD bridge pier is validated through bidirectional quasi-static and pseudodynamic tests performed on a 30% scale specimen. The seismic performance of the DAD pier is compared to that of a conventional ductile pier, and it is shown that it is possible to achieve 90% confidence that the DAD pier will survive a design basis earthquake without sustaining any damage.

Wolski et al. investigate a new beam-to-column connection for earthquake-resistant moment-resisting frames (MRFs) in “Experimental Study of a Self-Centering Beam-Column Connection with Bottom Flange Friction Device.” The connection has a beam bottom flange friction device (BFFD) and posttensioned (PT) high-strength steel strands that produce self-centering connection behavior running parallel to the beam. A series of seven large-scale tests were performed to investigate the effect of the BFFD friction force and other connection details on the performance of the connection under cyclic loading. The test results indicate that the BFFD provides reliable energy dissipation and that the connection remains damage free under the design earthquake. In “Performance-Based Seismic Design of Steel MRFs with Elastomeric Dampers,” Lee et al. examine the effects of SMRF properties and damper design criteria on the supplemental damper design. Nonlinear dynamic time history analyses show that SMRFs with dampers designed using a simplified design procedure achieve the specified seismic performance objectives, and that elastomeric dampers are more effective when used in a more flexible SMRF. Criteria that allow limited inelastic behavior $(R=2)$ but limit the story drift to 1.5% under the design basis earthquake are shown to lead to the most effective damper design.

Hutchinson and Wang propose a method for “Evaluation of Crack Spacing in Reinforced Concrete Shear Walls” subjected to lateral demands. The method extends an existing methodology based on both strength and fracture energy criteria. The extension allows the method to be applied to RC members under a plane stress condition with orthogonally placed reinforcement. Evaluation of the model with experimental data extracted from the literature indicates that the method can predict the average crack spacing with reasonable accuracy, not only in the crack initiation stage, but also in the stabilization stage.

An experimentally based relationship corresponding to the splitting mode of bond failure is developed by Harajli in “Bond Stress–Slip Model for Steel Bars in Unconfined or Steel, FRC, or FRP Confined Concrete under Cyclic Loading.” The model accounts for both unconfined and moderately confined concrete and incorporates the effect of several critical bond parameters such as the diameter of steel bars, the ratio of concrete cover to bar diameter, the concrete compressive strength, the type of confinement such as steel ties, fiber-reinforced concrete (FRC), and fiber-reinforced polymer (FRP) jackets, and the area or content of confining reinforcement. Results predicted by the model are shown to be in good agreement with experimental data.

A softened strut-and-tie model is presented by Campione to simulate the “Performance of Steel Fibrous Reinforced Concrete Corbels Subjected to Vertical and Horizontal Loads.” The study considers both normal and high-strength concrete and includes the influence of factors such as fiber percentage and the arrangement and percentage of the main and horizontal stirrup steel bars. The proposed model is validated with experimental data available in the literature and also numerical results obtained by using a nonlinear finite-element program.

A new strengthening technique is proposed by El-Tawil and Ekiz involving attaching a core composed of mortar blocks to the braces and then wrapping the entire system with carbon fiber-reinforced polymer (CFRP) sheets in “Inhibiting Steel Brace Buckling Using Carbon Fiber-Reinforced Polymers: Large-Scale Tests.” Results of experimental testing on seven specimens subjected to reversed axial loading indicate that it is feasible to achieve buckling restrained response up to 2% interstory drift. It is observed that performance of the strengthening scheme depends on the number of longitudinal fibers, the size of the core material, presence of bond between the steel plate and core material, existence of extra stitch plates for double angle members, and presence of transverse CFRP layers at the member ends.

In “Design of Steel Equal Angle Lintels,” Trahair reviews past research on single equal angle beams used as lintels and develops an improved method of predicting their strengths, which includes the effects of initial twist rotations, eccentric loads, and large twist rotations, and utilizes the plastic capacities of compact beams. The strengths predicted are significantly higher than those of previous approximations. More accurate strength approximations are proposed, and suggestions are made for serviceability design.

Chan and Gardner report on findings from a series of precise column buckling tests on hot-finished steel elliptical hollow sections in “Flexural Buckling of Elliptical Hollow Section Columns.” Twenty-four flexural buckling tests were carried out about both the minor and major axes on specimens whose nondimensional column slenderness varied between 0.19 and 1.58. The test results are supplemented by 158 numerically generated results so as to consider a wider range of geometries. Design rules for the member buckling resistance of elliptical hollow section columns are proposed and verified by means of reliability analysis. Zhu and Young present results from experimental and numerical investigations in their paper “Design of Aluminum Alloy Flexural Members Using Direct Strength Method.” Tests were performed on 10 different sizes of square hollow sections subjected to pure bending. A validated finite-element model was used in parametric studies of aluminum alloy beams of square hollow sections. Based on comparing the experimental and numerical bending strengths with the design strengths calculated using the current American, Australian/New Zealand, and European specifications for aluminum structures, design rules are proposed for aluminum alloy square hollow section beams based on the current direct strength method.

Fritz et al. utilize a database of building natural period and damping to provide a rich context for analyzing one-of-a-kind systems in “Predictive Models from Statistically Nonconforming Databases.” The approach is based on the statistical framework of generalized linear models and is structured in a manner to allow for engineering insights into the model. The database is statistically nonconforming since the data are nested and unbalanced, because the measurements come from different excitation sources and are unevenly distributed among different building categories, and the variability is nonuniform. In the companion paper, “Predictive Models for the Median and Variability of Building Period and Damping,” it is shown how this approach can be applied to develop comprehensive models for building natural period and damping. It is concluded that the period models are in general agreement with those currently used, with model parameters that are in terms of height, material, and lateral force-resisting system. The damping models show a decrease in damping as building height increases, and, for steel and reinforced structures, a twofold decrease is observed in damping for earthquake excitations as opposed to lower-amplitude excitations.

In “Seismic Reliability Analysis of Diagonal-Braced and Structural-Panel-Sheathed Wood Shear Walls,” Li et al. utilize a response surface method with importance sampling to evaluate commonly used shear walls in modern post-and-beam wood buildings. The seismic response of the shear walls was carried out using a recently developed shear wall model whose parameters were calibrated using a reversed cyclic test database. Peak wall drift was chosen as the performance criterion to estimate the failure probabilities of the walls with respect to two performance expectations. Results from numerical simulations indicate that the seismic reliability of the structural-panel-sheathed walls was higher than that of the diagonal-braced walls.

In “Strategic Network Utilization in a Wireless Structural Control System for Seismically Excited Structures,” Swartz and Lynch propose wireless sensors for use in large-scale structural control systems to keep costs low and to improve system scalability. Since bandwidth and range limitations of the wireless communication channel render traditional centralized control solutions impractical for the wireless setting, a partially decentralized linear quadratic regulation control scheme is developed that employs redundant state estimation as a means of minimizing the need for the communication of state data between sensors. The method is validated using numerical simulations of a seismically excited six-story building model with ideal actuators, and additional experimental validation is conducted using a full-scale physical realization of the six-story building. A wireless sensor network commanding magneto-rheological (MR) dampers is shown to be effective in controlling a multistory structure using the proposed partially decentralized control architecture.