Editor’s Note

A three-part paper on unreinforced masonry (URM) buildings leads off this issue of the Journal. Yi et al. present experimental findings from “Lateral load tests on a two-story unreinforced masonry building.” Results from the full-scale quasi-static tests that examined both global and local behavior indicate major improvements are necessary in current FEMA-356 provisions for URM buildings. In the second paper, the authors investigate the applicability of both 2D and 3D modeling in the analysis of URM structures. Since there was little coupling between parallel in-plane walls, 2D analytical models were found to be an adequate representation of the test structure. The authors conclude that a simple rigid body analysis is sufficient for a quick estimate, that a 3D finite-element model is needed only for in-depth investigation of important projects, and that 2D pushover analysis is best for seismic and retrofit evaluation of existing URM structures. The final part, authored by Moon et al., proposes design “Recommendations for seismic retrofit and evaluation of low-rise URM structures.” Based on findings from experimental testing, modifications to existing FEMA-356 guidelines for in-plane analysis of perforated URM walls are suggested. The proposed modifications incorporate global issues such as flange participation, overturning effects and global rocking, and also provide a better representation of failure modes.

The first two papers in this section deal with applications of the strut-and-tie model while the third paper is concerned with unbalanced moments in interior flat plate-to-column connections.

A cast modular connector (MC) for use as an energy dissipating detail in bolted steel moment frames is proposed by Fleischman and Sumer in their paper “Optimum arm geometry for ductile modular connectors.” The MC utilizes a series of variable arms to minimize plastic strain demand and a stiff end-region joined by a base to eliminate bolt prying forces. The parametric study reported in this paper results in optimum geometric ratios covering width reduction, length-to-thickness, aspect ratio, and fillet radius. Results from 16 full-scale tests, consisting of either “T” or “N” configurations, are reported by Dawe et al. in “Experimental study of offset HSS connections.” Failure in all cases resulted from localized large deflections of the flange face and sidewalls of the compression chord. The reduction in capacity in T-connections by offsetting a member by as much as 17% of the chord width from the central plane of the truss was marginal, while a slight increase in ultimate strength of N-connections was observed when diagonal members were offset by 8%.

Wong presents an elastic method to consider the “Effect of torsion on limiting temperature of steel structures in fire.” The critical temperature of the structure is assumed to correspond to the ultimate failure of the member at the lowest limiting temperature, and the proposed procedure is equivalent to finding the location of the first plastic hinge in a general plastic analysis. The formulation considers the effects of degradation of mechanical properties of steel caused by temperature changes resulting from fire, and the failure criterion considers combined design actions including the effects of torsion.

“Seismic reliability of low-rise nonsymmetric woodframe buildings” is investigated by Wang and Foliente through combined experimental and analytical studies of single- and two-story L-shaped structures. Uncertainties associated with ground motion characteristics and structural modeling parameters are determined to be among the primary sources influencing seismic demand. Coupling of torsion with bidirectional excitation is also found to result in response magnification. Marxhausen and Stalnaker present findings from a comprehensive experimental study on “Buckling of conventionally sheathed stud walls.” Sheathing materials such as oriented strand board, drywall, and fiberboard, when properly attached, are shown to be capable of resisting weak-axis buckling.

A total Lagrangian approach is utilized by Pi et al. in their paper “Second-order nonlinear inelastic analysis of composite steel-concrete members. I: Theory:” This paper provides a method to analyze composite members that considers slip between steel and concrete caused by the flexible shear connection at the interface. The proposed constitutive model, which incorporates the effects of slip at the interface on the von Mises yield surface, associated flow rule, and isotropic hardening, can be used with any uniaxial material model for steel and concrete. The implementation of the incremental-iterative procedure in a finite-element framework is described in a companion paper. A consistent tangent modulus matrix is derived to avoid error accumulation during the solution process by using standard procedures. Comparisons between experimental and numerical solutions validate the formulations.

The effects of large initial static sag deflections caused by self-weight are investigated by Pulngern et al. in the paper “On free vibrations of variable-arc-length beams: Analytical and experimental.” The formulations represent small amplitude vibration around the static sag configuration. The vibration eigenvalue problem is solved using inverse iteration techniques.

“Improving full-scale transmission tower design through topology and shape optimization” by Shea and Smith discusses the application and enhancement of structural topology and shape annealing (STSA) to reduce the structural mass of full-scale lattice towers. The proposed method produced design improvements in both the structural mass and the number of joints and primary members.

A methodology for “Semiactive fuzzy control of the seismic response of building frames” using multiple semiactive hydraulic dampers (SHD) is presented by Bhardwaj and Datta. It is shown that a fuzzy rule base can provide an efficient control strategy and that an optimum combination of parameters for maximum control is different for different response measures of interest. Results of numerical simulations to test a damage detection method are described by Park et al. in “Blind test results for nondestructive damage detection in a steel frame.” The projected damage locations and severity estimates in a blind prediction of the response of a four-story steel frame are shown to match observed damage with reasonable accuracy.

The final technical paper in this issue by Biondini et al. presents a general approach for “Probabilistic service life assessment and maintenance planning of concrete structures.” Monte Carlo simulation is used to account for randomness in the primary structural parameters, and the time-variant reliability, which accounts for the diffusive attack of external aggressive environments, is computed with respect to selected structural response measures. The results of the lifetime durability analysis are used to select the most economical rehabilitation strategy based on the prescribed target structural service life.

The issue also includes a discussion by Tavio on the paper “Interactive mechanical model for shear strength of deep beams” by Tang and Tan that appeared in the October 2004 issue of the Journal. The discusser points to possible errors and omissions in the original paper with respect to the presented experimental data, equations, and cited references. The original writers clarify the questions and concerns raised by the discussers.

Ahn, I-S., Chen, S. S., and Dargush, G. F. (2006). “Dynamic ratcheting in elastoplastic single degree-of-freedom systems.” J. Eng. Mech., 132(4).

Huang, C-T., and Iwan, W. D. (2006). “Equivalent linearization for the nonstationary response analysis of nonlinear systems with random parameters.” J. Eng. Mech., 132(5).

Katafygiotis, L., and Cheung, S. H. (2006). “Domain decomposition method for calculating the failure probability of linear dynamic systems subjected to Gaussian stochastic loads.” J. Eng. Mech., 132(5).

Kircher, C. A., Whitman, R. V., and Holmes, W. T. (2006). “HAZUS earthquake loss estimation methods.” Nat. Hazards Rev., 7(2).

Krishnan, S., and Hall, J.F. (2006a). “Modeling of steel frame buildings in three dimensions. I: Panel zone and plastic hinge beam elements.” J. Eng. Mech., 132(4).

Krishnan, S., and Hall, J. F. (2006b). “Modeling of steel frame buildings in three dimensions. II: Elastofiber beam element and examples.” J. Eng. Mech., 132(4).

Lupoi, G., Franchin, P., Lupoi, A., and Pinto, P. E. (2006). “Seismic fragility analysis of structural systems.” J. Eng. Mech., 132(4).

Mo, Y. L., and Fan, Y-L. (2006). “Torsional design of hybrid concrete box girders.” J. Bridge Eng., 11(3).

Phelan, R. S., Sarkar, P. P., and Mehta, K. C. (2006). “Full-scale measurements to investigate rain-wind induced cable-stay vibration and its mitigation.” J. Bridge Eng., 11(3).

Tobita, T., and Sawada, S. (2006). “Rotation response of a rigid body under seismic excitation.” J. Eng. Mech., 132(4).

Tremblay, R., and Mitchell, D. (2006). “Collapse during construction of a precast girder bridge.” J. Perform. Constr. Facil., 20(2).

Van de Lindt, J. W., and Gupta, R. (2006). “Damage and damage prediction for wood shear walls subjected to simulated earthquake loads.” J. Perform. Constr. Facil., 20(2).

Warn, G. P. and Whittaker, A. W. (2006). “Property modification factors for seismically isolated bridges.” J. Bridge Eng., 11(3).

Zhu, Z., Ahmad, I., and Mirmiran, A. (2006). “Seismic performance of concrete-filled FRP tube columns for bridge substructure.” J. Bridge Eng., 11(3).