EDITOR’S NOTE

“Wind-Induced Self-Excited Loads on Bridges,” by Chen et al., opens this issue of the journal. A vibration excitation system was designed and built to facilitate forced vibration experiments in a wind tunnel to investigate dynamic effects on flutter derivates and aerodynamic forces on bridge sections. Although flutter derivates were found to be moderately dependent on amplitude and frequency, the response of bluff sections contained relatively large higher-order harmonics. The effectiveness of semiactive tuned liquid column damper (TLCD) and hybrid viscous fluid damper-TLCD control system is investigated by Kim and Adeli in “Wind-Induced Motion Control of 76-Story Benchmark Building Using the Hybrid Damper-TLCD system.” The hybrid system is shown analytically to perform better than the semiactive TLCD system under various wind loading conditions.

An explicit finite element numerical model for “Large Displacement Analysis of Cyclically Loaded Inelastic Structures” is proposed by Chiou and Hsiao. The convected material frame approach is used for geometric nonlinearities, whereas the Dafalias-Popov two-surface model is adopted to characterize uniaxial material nonlinearities. Numerical simulations of nonlinear transient response of frame structures demonstrate the effectiveness of the approach. Alemdar and White present “Displacement, Flexibility, and Mixed Beam-Column Finite-Element Formulations for Distributed Plasticity Analysis” of planar frame structures. The paper examines similarities and differences in the element formulations associated with the element natural (or deformation) degrees of freedom. Numerical examples are provided to compare the performance of the different element formulations.

Yun and Kim develop a methodology for “Optimum Design of Plane Steel Frame Structures Using Second-Order Inelastic Analysis and a Genetic Algorithm.” The objective and penalty functions for the genetic algorithm are expressed, respectively, as the weight of the steel frames and the constraint functions incorporating requirements for load-carrying capacity, ductility, and serviceability. The proposed method is validated by comparing design solutions with results obtained by using AISC-LRFD elastic analysis, geometric nonlinear analysis, and plastic zone analysis methods. “Nonlinear Effect on Instability of Steel Columns under Dynamic Axial Loads” is investigated by Yabuki et al. Dynamic instability is shown to be influenced by material nonlinearity, particularly when the forcing frequency is smaller than the fundamental lateral frequency of the column.

A superposed nonlinear force-deformation model and a simplified model are proposed by Fukumoto and Morita in “Elasto-Plastic Behavior of Panel Zone in Steel Beam-to-Concrete Filled Steel Tube Column Moment Connections,” on the basis of experimental tests. A method to estimate the capacity of the panel zone is also proposed. Predictions using the simplified model were found to agree with the superposed model up to the concrete core ultimate strength. Lee et al. present results from tests on bolted and welded connections in “Effects of Panel Zone Strength and Beam Web Connection Method on Seismic Performance of Reduced Beam Section Steel Moment Connections.” Panel zones with welded web connections were found to perform better than bolted connections. A criterion is recommended for a balanced panel-zone strength that improves the rotation capacity while limiting lateral torsional buckling in the beam. “Experimental Studies of Wide Flange Beam to Square Concrete-Filled Tube Column Joints with Stiffening Plates around the Column” are reported by Park et al. An analytical yield line method is developed to predict the nominal strength of the connection, and results from the experimental program indicate that the proposed strength equation provides a reasonable prediction.

A two-part paper examining size effects in shear failure of beams is put forth by Bazant and Yu in “Designing against Size Effect on Shear Strength of Reinforced Concrete Beams without Stirrups.” The first part demonstrates that a general but approximate mathematical form of the size effect law is similar to that established for other quasi-brittle materials and that the maximum load is attained only after large fracture growth rather than fracture initiation. The second part of the paper presents experimental verification by least-square fitting of existing individual data sets with a broad size range. The proposed formula also agrees with test data on the effects of shear span, reinforcement ratio, and aggregate size.

The sensitivity of several damage detection, localization, and quantification methods is investigated by Huth et al. in “Damage Identification Using Modal Data: Experiences on a Prestressed Concrete Bridge.” The mode shape area index was determined to be the most sensitive damage index detection approach. The study also found that early damage detection is difficult and that damage detection on the basis of changes in the flexibility matrix performed better than natural frequencies and mode shapes alone. On the basis of findings from testing of push-off specimens, “Shear Friction Capacity of Concrete with External Carbon FRP Strips” is reported by Saenz and Pantelides. The shear friction capacity increased significantly over plain concrete without steel reinforcement; however, no additional shear capacity could be developed with a four-sided scheme instead of a two-sided scheme. An analytical method that combines heat transfer analysis and nonlinear structural analysis for assessing the “Structural Fire Performance of Concrete and Shotcrete Tunnel Liners” is developed by Caner et al. Techniques to minimize fire damage are recommended, and methods to repair fire-damage concrete are discussed.

The issue concludes with two short technical notes. The first note, by Bajaj and Mendis, discusses “A New Method to Evaluate the Biaxial Interaction Exponent for RC Columns.” The approach results in values of the interaction exponent being similar to the PCA load contour and the Bresler methods. The second technical note, and the final paper in this issue of the journal, contains a simplified method for “Estimating Periods of Vibration of Buildings with Coupled Shear Walls.” Written by Wang and Wang, the note confirms that the resulting equation for the natural vibration of such structures is the fourth-order Sturm-Liouville differential equation. The method provides a more accurate means of employing code formulas for determining the peak seismic design shear forces in buildings.

Huang, C.-T., and Iwan, W. D. (2005). “Generalized damped wave approach for evaluating seismic shear demands.” J. Eng. Mech., 131(12).

Kim, S., and Sridharan, S. (2005). “Analytical study of bifurcation and nonlinear behavior of sandwich columns.” J. Eng. Mech., 131(12).

Li, H., Mao, C.-X., and Ou, J.-P. (2005). “Strain self-sensing property and strain rate dependent constitutive model of austenitic shape memory alloy: Experiment and theory.” J. Mater. Civ. Eng., 17(6).

Lokuge, W. P., Sanjayan, J. G., and Setunge, S. (2005). “Stress-strain model for laterally confined concrete.” J. Mater. Civ. Eng., 17(6).

Mohammadi, Y., and Kaushik, S. K. (2005). “Flexural fatigue-life distributions of plain and fibrous concrete at various stress levels.” J. Mater. Civ. Eng., 17(6).

Ryan, K. L., Kelly, J. M., and Chopra, A. K. (2005). “Nonlinear model for lead-rubber bearings including axial-load effects.” J. Eng. Mech., 131(12).

Val, D. V. (2005). “Effect of different limit states on life-cycle cost of RC structures in corrosive environmentEffect of different limit states on life-cycle cost of RC structures in corrosive environment.” J. Infrastruct. Syst., 11(4).