Editor’s Note

This issue of the Journal consists of 16 technical papers and a technical note. The primary themes of papers that appear in this issue are dynamic effects, which include wind and seismic effects, and metal structures.

This issue of the Journal opens with a paper summarizing findings from a project to monitor the full-scale response of representative tall buildings. Kijewski-Correa et al. provide several interesting insights in “Validating Wind-Induced Response of Tall Buildings: Synopsis of the Chicago Full-Scale Monitoring Program,” wherein observed data from three tall buildings are compared with wind-tunnel and finite-element models generally used in design. The comparison indicates that standard modeling assumptions reliably predicted the fundamental period of vibration of the uncoupled steel building but could not be validated for the concrete building. Damping levels assumed at 1% for serviceability design were found to be reasonable for the uncoupled steel building but conservative for the coupled steel and reinforced concrete building. Predicted accelerations from wind tunnel testing revealed that the full-scale data had some scatter but followed the general trend of the wind-tunnel predictions.

A 2-part paper examining seismic design forces in nonstructural components is presented by Singh et al. The first part deals with rigid nonstructural components and examines the design formulas prescribed in the 2003 NEHRP provisions. It concludes that the current provisions are building-independent and overly conservative. This conservatism is reduced by new period-dependent formulations introduced by the writers. The second part deals with flexible nonstructural components in building structures. It proposes a new method to compute the seismic design coefficients that use the dynamic characteristics of both the component and the supporting structure. The proposed expressions include the effect of possible resonance with higher modes. In both cases, the proposed expressions are validated by comprehensive numerical studies of several buildings with varying fundamental periods.

Response studies using frequency domain, joint time frequency, system identification, and simple damage detection analyses are performed by Rodgers and Celebi in “Seismic Response and Damage Detection Analyses of an Instrumented Steel Moment-Framed Building.” The response of the building is found to be characterized by larger accelerations in the middle and lower levels than at the roof, beating in the response, elliptical particle motion, and significant torsion despite its symmetrical geometry. The analyses conclude that the structure responded elastically in the Northridge event and did not sustain any damage. Chang and Kawakami examine the “Effects of Ground Motion Parameters and Cyclic Degradation Behavior on Collapse Response of Steel Moment-Resisting Frames.” Artificial accelerograms with identical Fourier amplitude spectrum were used, and the peak intensity at which the systems survived collapse was observed. Results from the numerical study indicate that in the case of moderate degradation, the maximum intensity for far-field motions not to collapse the systems were larger than those for near-field motions. This trend increased with severe degradation but reversed with slight degradation.

“Probabilistic Demand Models and Fragility Curves for Reinforced Concrete Frames” are developed by Ramamoorthy, Gardoni, and Bracci to assess the seismic vulnerability of concrete frame buildings designed only for gravity loads. Fragility curves are then constructed for the same frames retrofitted by column strengthening. Capacity limit states are established by using FEMA-356 guidelines. The analytical study demonstrates the effectiveness of column strengthening in reducing the probability of failure. Holler and Meskouris investigate the seismic response of granular material silos to verify load assumptions in current European codes in “Granular Material Silos under Dynamic Excitation: Numerical Simulation and Experimental Validation.” The numerical model incorporates components to represent the granular material content, the silo wall, and their interface. Soil-structure interaction effects were also modeled. The model is validated with observed data from shake-table experiments. It is shown that the Eurocode provisions are adequate for slender silos, but the assumed active mass for squat silos is overestimated, leading to conservative results.

In “Mechanics of Web Panel Postbuckling Behavior in Shear,” Yoo and Lee revisit the fundamental assumption that the compressive stresses that develop in the direction perpendicular to the tension diagonal do not increase further after elastic buckling has taken place. On the basis of detailed nonlinear finite element analyses, the writers contend that the diagonal compression continuously increases, thereby producing in the web panel a self-equilibrating force system that does not depend on the flanges and stiffeners. Tikka and Mirza propose a “Nonlinear EI Equation for Slender Composite Columns Bending about the Minor Axis” to replace the current provisions in the American Concrete Institute (ACI) building code. The equation is derived from stiffness data generated with approximately 12,000 isolated composite square columns, each with a different combination of specified properties of variables. The columns considered in the study were subjected to short-term ultimate loads and equal and opposite end moments causing symmetrical single-curvature bending.

Azzam and Menzemer study the effects of residual stresses on the behavior of welded structures subjected to cyclic loads in “Residual Stress Measurement of Welded Aluminum Light Pole Supports.” Two details were evaluated: three cast shoe base socket connections to extruded tube and two through plate socket connection joints using the hole drilling technique. The power series method to convert strains to stresses is found to be more reliable than the integral method primarily because of its sensitivity to human and instrumentation errors. Estimating internal forces in lateral bracing members and internal cross frames is the subject of the paper “Interaction of Top Lateral and Internal Bracing Systems in Tub Girders” by Kim and Yoo. Significant coupling action between single diagonal (SD) bracing members and internal cross-frame members is found to occur in the case of an SD lateral bracing and internal cross frames placed at odd-numbered panel spacing. A method to compute the brace forces developed in both SD lateral bracing and K-shaped internal cross-frame members subjected to bending action is proposed.

Results from a unique three-dimensional experiment are described by Goto, Jiang, and Obata in “Stability and Ductility of Thin-Walled Circular Steel Columns under Cyclic Bidirectional Loading.” The experimental system is characterized by a 3D hinge and a 3D transducer, which enable 3D force components to be applied to the column specimen by precisely considering geometric nonlinearity. It is observed that the strength and ductility of columns decrease considerably under bidirectionally applied cyclic circular loads compared with conventional cyclic unidirectional loads. Nguyen, Fung, and Young present a combined experimental-analytical study of the “Strength and Behavior of Cold-Formed Steel Z-Sections Subjected to Major Axis Bending.” Specimen failure was typically characterized by shear-bending interaction at the loading points. A finite-element model was developed to simulate the experimental observations but the authors recommend finite element analyses of cold-formed sections only if the model is calibrated with physical test results.

A theoretical and experimental study on “Creep Buckling of Shallow Parabolic Concrete Arches” is presented by Wang, Bradford, and Gilbert. Equilibrium and buckling equations of an arch with horizontal spring supports are derived in closed form by using a virtual work formulation. Long-term tests on three 4.25-meter-span arches under sustained loading are used to validate the theory and provide benchmark data for calibration. Prescriptive equations are proposed to assess the influence of various parameters on creep buckling and nonlinear response of arches.

“Homogenization Approach for the Limit Analysis of Out-of-Plane Loaded Masonry Walls” by Milani, Lourenco, and Tralli uses an anisotropic failure surface that is based on a polynomial representation of the stress tensor components combined with finite-element triangular elements for the out-of-plane analysis of masonry panels. The ensuing limit analysis permits the identification of the internal force distribution at critical sections and also permits obtaining collapse modes and failure loads.

The minimization of material volume subject to the constraints of permissible stress, maximum allowable deflection, and membrane thickness are addressed by Khire et al. in “Study of a Honeycomb-Type Rigidified Inflatable Structure for Housing.” The effects of various design parameters such as cell size, material properties, and membrane thickness are discussed with the objective of investigating the feasibility of rigidized inflatable structures for housing applications.

The heightwise distribution of lateral loads in seismic design is investigated by Moghaddam and Mohammadi in “More Efficient Seismic Loading for Multidegrees of Freedom Structures.” The adequacy of several lateral load patterns is examined, and a unique strength distribution pattern is introduced that leads to the least amount of ductility demand.

Burgueno, R., and Wu, J. (2006). “Membrane-based forms for innovative FRP bridge systems through structural optimization.” J. Compos. Constr., 10(5).

Challamel, N. (2006). “On the comparison of Timoshenko and shear models in beam dynamics.” J. Eng. Mech., 132(10).

Chen, X., and Kareem, A. (2006). “Revisiting multimode coupled bridge flutter: Some new insights.” J. Eng. Mech., 132(10).

Khoo, H. A., Hrudey, T. M., and Cheng, J. J. R. (2006). “Microvoid damage model with material dilation for ductile fracture.” J. Eng. Mech., 132(10).

Law, S. S., Li, X. Y., and Lu, Z. R. (2006). “Structural damage detection from wavelet coefficient sensitivity with model errors.” J. Eng. Mech., 132(10).

Oh, B. H., Kim, E. S., and Choi, Y. C. (2006). “Theoretical analysis of transfer lengths in pretensioned prestressed concrete members.” J. Eng. Mech., 132(10).

Rasheed, H. A., Larson, K. H., and Peterman, R. J. (2006). “Analysis and design procedure for FRP-strengthened prestressed concrete T-girders considering strength and fatigue.” J. Compos. Constr., 10(5).

Yu, T., Wong, Y.-L., Teng, J.-G., Dong, S.-L., and Lam, E. S. S. (2006). “Flexural behavior of hybrid FRP-concrete-steel-double-skin tubular members.” J. Compos. Constr., 10(5).