Editor’s Note

The issue opens with a paper by Praveen Malhotra examining the “Return Period of Recorded Ground Motion.” It is argued that ground motions produced by earthquakes have calculable return periods that can vary at different sites. A systematic procedure to establish the return period of ground motions is proposed and illustrated in a case study utilizing the Templeton Hospital record from the 2003 San Simeon, California earthquake. In the next paper, a new measure of seismic demand referred to as “Generalized Interstory Drift Spectrum” is presented by Miranda and Akkar. Based on a continuous linear elastic model that incorporates both flexural and shear modes, the writers develop a design tool for estimating drift demands in buildings.

Christenson et al. examine the protection of flexible building structures in “Coupled Building Control Considering the Effects of Building/Connector Configuration.” When building frequencies nearly match or a coupling link is placed near a vibratory node active control is found to provide improved performance over passive control. Inoue et al. propose an innovative structural system composed of metallic-yielding dampers in beam-to-column connections in their paper “Seismic-Resistant Weld-Free Steel Frame Buildings with Mechanical Joints and Hysteretic Dampers.” The proposed system is verified through experimental testing. A procedure for determining the number of velocity-dependent energy dissipation devices required to meet a given target displacement is described by Kim and Choi in “Displacement-Based Design of Supplemental Dampers for Seismic Retrofit of a Framed Structure.” The performance of model structures retrofitted by the proposed method is evaluated through nonlinear time-history analyses.

Seismic fragility curves derived from analytical studies of three different building models and 32 short-distance ground motions are discussed by Chaudhuri and Hutchinson in “Fragility of Bench-Mounted Equipment Considering Uncertain Parameters.” The shape and distribution of the fragility curves are shown to be influenced by the characteristics of both the building and the supporting bench.

Repetto and Solari develop an advanced broad-band formulation to assess “Bimodal Alongwind Fatigue of Structures.” Applying the cycle-counting method, two discrete cyclic histogram expressions are proposed that provide an upper and lower bound on the fatigue damage. Since the gap between the two bounds may be significant, the formulation is refined based on a bi-modal representation of the alongwind-induced stress power spectral density functions. The analytical formulation is validated with numerical solutions obtained through Monte Carlo simulations. Kopp and Chen develop a data handling system in “Database-Assisted Design of Low-Rise Buildings: Aerodynamic Considerations for a Practical Interpolation Scheme.” The scheme provides a means to obtain wind pressure time series beyond the basic configurations available in the database. Interpolation is performed only over the geometric parameters defining the external surfaces of the building.

Coelho et al. describe the “Finite Element Modeling of the Nonlinear Behavior of Bolted T-Stub Connections.” Two types of T-stub elements are considered: rolled profiles that are cut along the web; and flange and web plates that are produced by continuous fillet welding. Experimental data are utilized to calibrate the models. A parametric study provides insight into the failure modes and deformation capacity of various specimens.

A “Strut-and-Tie Design Methodology for Three-Dimensional Reinforced Concrete Structures” is presented by Leu et al. based on a refined evolutionary structural optimization approach. The stiffness of struts is computed from an evolved topology of a finite-element model while the compressive strength of the struts and nodal zones are evaluated using Ottosen’s four-parameter strength criterion. Two design examples demonstrate the suitability of the proposed procedure.

Suthiwarapirak and Matsumoto propose a new methodology for “Fatigue Analysis of RC Slabs and Repaired RC Slabs Based on Crack Bridging Degradation Concept.” The bridging stress degradation of concrete cracks is introduced as a primary mechanism for the propagation of cracks that induce failure. Analytical studies indicate that RC slabs under moving loads exhibit shorter fatigue life than under fixed pulsating loads. An analytical procedure for predicting the “Shear Response of Concrete-Filled FRP Composite Cylindrical Shells” is developed by Burgueño and Bhide. The layered sectional analysis incorporates a smeared shear modulus for cracked concrete and extension/shear coupling effects of anisotropic FRP laminates. Following the validation of the model with experimental data, parametric studies on the influence of concrete properties, axial loads, and FRP laminate design are presented.

The “Safety Assessment of Concrete Tunnel Linings under Fire Load” is investigated by Pichler, Lackner, and Mang. Dehydration of concrete under high temperature is found to be the critical factor controlling limit-state behavior. A thermo-chemo-mechanical material model is employed to carry out the evaluation and assess the state of dehydration in the lining after fire exposure.

In contrast to methods based purely on geometry, Hernández-Montes, Jurado-Piña, and Bayo propose a new “Topological Mapping for Tension Structures” that combines simple topological networks and the force density method. The topology-based pin-jointed network does not require an initial guess of the equilibrium position and leads to different choices of the final configuration.

Chan and Wang integrate nonlinear cracking analysis methods with an optimization technique for “Nonlinear Stiffness Design Optimization of Tall Reinforced Concrete Buildings under Service Loads.” A probability-based effective stiffness method is employed to identify cracked members, and the design optimization is based on optimality criteria that minimizes the cost of the structure while satisfying interstory drift and member size constraints. Probabilistic continuous performance indicators and probabilistically defined objectives and constraints form the basis of the paper “Probabilistic Lifetime-Oriented Multiobjective Optimization of Bridge Maintenance: Single Maintenance Type” by Neves et al. The problem is solved using multiobjective genetic algorithms and Latin hypercube sampling. Results indicate that preventive maintenance actions alone lead to feasible solutions within a relatively small objective space while essential maintenance actions allow for a wider range of feasible solutions.

Three discussions are included in this issue. The first discussion, by Yin Zhou, on a paper by Chen and Kareem that appeared in the October 2004 issue of the Journal raises concerns on the practical applicability of the proposed Equivalent Static Wind Load (ESWL) model. The authors clarify the background and motivation for their work and indicate that dynamic response analysis must be carried out during the development process of the equivalent loading to ensure that the ESWL produces conservative or comparable results. Additional discussions concern the paper “Influence of Foundation Flexibility on $R_{\mu }$ and $C_{\mu }$ ” by Avilés and Pérez-Rocha that appeared in February 2005. Ghannad and Jahankhah question the validity of the conclusion that for relatively squat buildings, the same reduction factors computed for fixed-base models are applicable for soft soils. Harden and Hutchinson, on the other hand, offer a simple approach to also account for foundation uplift, which was not included in the study. The authors clarify the issues raised by Ghannad and Jahankhah. On the question of incorporating foundation uplift, the authors point out that nonlinear SSI associated with structural yielding and foundation uplift are completely different phenomena, and the solution of the former is not necessarily applicable to the solution of the latter.

Almutairi, N.B., Hassan, M.F., Abdel-Rohman, M., and Terro, M. (2006). “Control of suspension bridge nonlinear vibrations due to moving loads.” J. Eng. Mech., 132(6).

Bernal, D. (2006). “Flexibility-based damage localization from stochastic realization results.” J. Eng. Mech., 132(6).

Korany, Y., and Drysdale, R. (2006). “Rehabilitation of masonry walls using unobtrusive FRP techniques for enhanced out-of-plane seismic resistance.” J. Compos. Constr. 9(3).

Saenz, N., and Pantelides, C. (2006). “Short- and medium-term durability evaluation of FRP-confined circular concrete.” J. Compos. Constr. 9(3).

Shi, X., Liang, J., and Burnett, E. (2006). “Mechanics and test study of two-dimensional flexible membranes.” J. Archit. Eng. 12(2).

Smyth, A.W., and Gjelsvik, A. (2006). “Energy capacity criterion for the design of columns against collapse.” J. Eng. Mech., 132(6).

Song, J., and Der Kiureghian, A. (2006). “Generalized Bouc-Wen model for highly asymmetric hysteresis.” J. Eng. Mech., 132(6).

Tufecki, E., and Dogruer, O.Y. (2006). “Exact solution of out-of-plane problems of an arch with varying curvature and cross section.” J. Eng. Mech., 132(6).