Editor’s Note

This issue of the Journal consists of four technical papers on analysis and computation, four papers on concrete structures, and three papers dealing with structural control. There are also two papers addressing topics on dynamic effects, one on seismic and one on windeffects, and two papers dealing with metal and composite structures. There is also a technical note discussing applications of the principle of stationary total potential, and a closure for a paper published in the October 2005 issue of the Journal.

The leadoff paper by Scott and Filippou proposes a derivation for the exact “Response Gradients for Nonlinear Beam-Column Elements under Large Displacements.” The element response formulation takes place in a corotational reference frame that displaces and rotates with the element, thus permitting the separation of nonlinear material from nonlinear geometric effects, as well as from the gradient response. Chaudhary et al. present “Hybrid Procedure for Cracking and Time-Dependent Effects in Composite Frames at Service Load.” The procedure is analytical at the element level and numerical at the structural level. It is anticipated that the proposed procedure will lead to considerable efficiency and savings in computational effort in cases of large composite structures. Kim and Engelhardt present the development of a nonprismatic beam element for modeling the elastic behavior of steel beams with reduced beam section (RBS) connections in “Nonprismatic Beam Element for Beams with RBS Connections in Steel Moment Frames.” The element can be used to accurately predict the elastic story drift of moment frames with RBS connections. The accuracy of the element is evaluated by comparisons with finite-element solutions. The final paper in this section deals with the bifurcation of the buckling path of shallow lattice domes. “Automatic Two-Stage Calculation of Bifurcation Path of Perfect Shallow Reticulated Domes” describes a two-stage analysis of the space structure without the modification of geometric modifications. The method is implemented in a combined materially and geometrically nonlinear finite–element method computer program. Results of the analysis are verified by comparison with experimental observations on two model domes.

Tan and Tjandra present test results on 12 two-span continuous RC T-beams strengthened with various types of external tendons in “Strengthening of RC Continuous Beams by External Prestressing.” Test results indicate that an increase in ultimate strength with sufficient ductility could be achieved using short tendons located over critical beam sections. It was also reported that beams strengthened with carbon fiber- reinforced polymer (FRP) tendons showed a similar response to those with steel tendons, while beams subjected to unsymmetrical loading exhibited larger deflections and lower ultimate load compared to those subject to symmetrical loading. “Direct Damage-Controlled Design of Concrete Structures” by Hatzigeorgiou and Beskos presents an integrated scheme for direct damage control in structural concrete design. The proposed methodology combines code-based, stress-strain relations with simple expressions for damage in structures constructed of plain concrete materials. Oh and Kim derive “Realistic Models for Local Bond Stress-Slip of Reinforced Concrete under Repeated Loading.” To this end, several series of experimental tests were conducted to explore bond-slip behavior under repeated loading. The results of the tests indicate that bond strength and slip at peak bond stress are not significantly influenced by repeated loading, provided that bond failure does not occur. Bamonte and Gambarova investigate the influence of size effect on the bonding of short deformed bars, embedded in normal-strength (NSC) and high-performance concretes (HPC) in “High-Bond Bars in NSC and HPC: Study on Size Effect and on the Local Bond Stress-Slip Law.” Test results from 48 cylindrical specimens reinforced with a single bar and subjected to a pull-out or push-in force indicate that bond exhibits a significant size effect dependence that can be described by Bazant’s general-type size-effect law.

The effectiveness of semiactive control using variable dampers is investigated by Lee and Kawashima in “Semiactive Control of Nonlinear Isolated Bridges with Time Delay.” A five-span viaduct with high-damping-rubber isolators is utilized for the analysis. The linear quadratic regulator (LQR) is employed to control the variable dampers, and a time delay compensation method is proposed to mitigate the degradation of control performance caused by time delay. The results indicate that semiactive control with variable dampers is effective in reducing the seismic response and provides similar performance by LQR active control. Setareh et al. describe the use of a semiactive magneto-rheological (MR) device in a pendulum tuned mass damper (PTMD) system to control excessive vibrations of building floors in “Semiactive Tuned Mass Damper for Floor Vibration Control.” Analytical and experimental studies are conducted to compare the performance of the semiactive pendulum tuned mass damper (SAPTMD) with its equivalent passive counterpart. Effects of human structure dynamic interactions on the performance of the SAPTMD were also investigated. Tait et al. present the results of bidirectional (2D) structure-tuned liquid damper (TLD) tests in “Effectiveness of a 2D TLD and Its Numerical Modeling.” Experimental results are used to verify the applicability of a unidirectional (1D) structure-TLD model to 2D structure-TLD analysis. Results of the study indicate that the structure-TLD model is capable of accurately predicting the structure-TLD response within the range of system response amplitudes tested.

The effect of the width thickness (w/t) ratio on the seismic behavior of cold-formed hollow structural section (HSS) bracing members is examined by Han et al. in “Seismic Behavior of HSS Bracing Members according to Width–Thickness Ratio under Symmetric Cyclic Loading.” The analysis results demonstrate that a displacement history during earthquake ground motion (EQGM) experienced by bracing members is symmetric in tension and compression. This study also showed that HSS bracing members with a small w/t ratio could not always guarantee larger energy dissipation capacity than bracing members with a larger w/t ratio. Lin et al. investigate the trajectories of compact and rod-type wind-borne debris in horizontal winds using a combination of experimental and numerical studies in “Trajectories of Wind-Borne Debris in Horizontal Winds and Applications to Impact Testing.” The results of the study indicate that the ratio of horizontal debris speed to wind gust speed is primarily a function of the horizontal distance traveled by the debris as it accelerates toward the wind speed.

Kowalkowski and Varma conducted experimental investigations to evaluate the effects of multiple cycles of damage followed by heating repair on the structural properties and fracture toughness of commonly used bridge steels in “Structural Properties of Steels Subjected to Multiple Cycles of Damage Followed by Heating Repair.” The results from the standard material tests indicated that multiple-damage-repair cycles have a relatively small influence on the elastic modulus, yield stress, and ultimate stress. However, the influence on ductility and fracture toughness of damage-repaired bridge steels is significant. “Full-Scale Test of Composite Frame under Large Cyclic Loading” by Nakashima et al. presents the results of a steel moment frame with a reinforced concrete (RC) floor slab subjected to cyclic loading and experiencing very large deformations. The primary objective of the study was to examine the interaction of the steel beam and the RC floor slab. Results of the study indicate that the steel beam moment capacity increases approximately 50% in positive bending due to its interaction with the RC floor slab.

Belenkiy discusses applications of the principle of stationary total energy in “Upper-Bound Solutions for Rigid-Plastic Plates and Slabs on Elastic Foundation by the Principle of Stationary Total Energy.” Several simple problems are considered for plates of different shapes and with different boundary conditions. The obtained solutions illustrate transformations of the form of deflections when the external load increases.

This issue also includes a closure by Liang et al. to their paper titled “Strength Analysis of Steel-Concrete Composite Beams in Combined Bending and Shear” that appeared in the October 2005 issue of the Journal. The authors clarify four points raised by the discusser. The points raised included the derivation of the shear connection stiffness, variation of the degree of shear connection along the span, the ability of the 3D beam element to simulate the local stress state in the concrete surrounding the shear stud, and clarification of the constitutive model used for the steel in the finite-element method analysis.

Bischoff, P. H. (2007). “Deflection calculation of FRP reinforced concrete beams based on modifications to the existing Branson equation.” J. Compos. Constr., 11(1).

ElGawady, M. A., Lestuzzi, P., and Badoux, M. (2007). “Static cyclic response of masonry walls retrofitted with fiber-reinforced polymers.” J. Compos. Constr., 11(1).

Grigoriu, M. (2007). “Multivariate distributions with specified marginals: Applications to wind engineering.” J. Eng. Mech., 133(2).

Ji, W., and Waas, A. M. (2007). “Global and local buckling of a sandwich beam.” J. Eng. Mech., 133(2).

Keller, T., Bai, Y., and Vallée, T. (2007). “Long-term performance of a glass fiber reinforced polymer truss bridge.” J. Compos. Constr., 11(1).

Reynders, E., Roeck, G., Bakir, P. G., and Sauvage, C. (2007). “Damage identification of the Tilff Bridge by vibration monitoring using optical fiber strain sensors.” J. Eng. Mech., 133(2).

Van de Lindt, J. W., Liu, H., and Pei, S. (2007). “Performance of a woodframe structure during full-scale shake table tests: Drift, damage, and effect of partition wall.” J. Perform. Constr. Facil., 21(1).

Wang, C-H., and Chang, S-Y. (2007). “Development and validation of a generalized biaxial hysteresis model.” J. Eng. Mech., 133(2).

Yan, Z., Pantelides, C. P., and Reaveley, L. D. (2007). “Posttensioned FRP composite shells for concrete confinement.” J. Compos. Constr., 11(1).