Editor’s Note

Papers in the opening issue of 2007 comprise topics covered by the following technical committees: wind effects, seismic effects, metal structures, concrete and masonry structures, and wood structures. Also included is a discussion and closure on a previously published paper that examined tension stiffening in shear panels.

Findings from data obtained from a Wind and Structural Health Monitoring System (WASHMS) installed in the Tsing Ma suspension bridge are presented in the leadoff, two-part paper by Xu et al. in “Dynamic Response of Suspension Bridge to Typhoon and Trains. I: Field Measurement Results.” All vehicles, except trains, were prohibited from running on the bridge as Typhoon York, the strongest typhoon since 1983, crossed Hong Kong. In the first part, wind characteristics and bridge responses are analyzed from anemometers and accelerometers for several cases of single and multiple moving trains. Measured field data are used in the second paper to verify the finite-element framework developed for predicting the time-domain response of coupled train and bridge systems in crosswinds. Wind forces acting on the bridge are generated using a fast spectral representation method based on field measurements and wind tunnel test results. Comparison between computed acceleration and displacement histories of the bridge are shown to be in reasonable agreement with observed response.

The aeroelastic response of lightly damped bridge systems consisting of fundamental vertical and torsional modes is investigated by Chen in “Improved Understanding of Bimodal Coupled Bridge Flutter Based on Closed-Form Solutions.” The proposed framework provides a formula for determining critical flutter velocity of bridges with generic bluff deck sections. The new formula gives a single parameter as a function of flutter derivatives to describe flutter efficiency of a given bridge section. The accuracy of the method is demonstrated through examples of long-span bridges with a variety of structural and aerodynamic characteristics.

Abrams et al. summarize results of a research program to evaluate the “Effectiveness of Rehabilitation on Seismic Behavior of Masonry Piers.” Flexural behavior of slender piers with and without rehabilitation and subjected to repeated and reversed in-plane deflections and varied axial compression is reported. The four rehabilitation techniques examined are adhered fiber-reinforced polymer strips, reinforced shotcrete overlay, ferrocement surface coating, and grouted reinforcing bars within drilled cores. Experimental results suggest that rocking behavior of unrehabilitated piers may be equal to or superior to that of retrofitted piers, and FEMA-356 guidelines to estimate seismic capacity of both bare and retrofitted masonry piers are generally conservative.

The “Seismic Performance of Square High-Strength Concrete Columns in FRP Stay-in-Place Formwork” is evaluated by Ozbakkaloglu and Saatcioglu. Large-scale HSC columns encased in FRP casings were tested under simulated seismic loading. Test parameters included the corner radius of the casing and the presence of internally placed FRP crossties. While the deformation capacity of HSC columns is increased by the FRP casing, the confinement effectiveness is found to be significantly influenced by the corner radius of the casings. In the next paper, Villaverde evaluates currently available analytical “Methods to Assess the Seismic Collapse Capacity of Building Structures: State of the Art.” The challenges associated with carrying out nonlinear time-history analyses of inelastic materials are highlighted, and the author concludes that further analytical and experimental research is needed before the collapse capacities of structures and the associated safety margin against collapse may be evaluated with confidence.

“Structures with Semiactive Variable Stiffness Single/Multiple Tuned Mass Dampers” are investigated by Nagarajaiah and Sonmez. The dynamic characteristics and effectiveness of SAIVS MTMD versus MTMD is compared through an analytical study for a range of frequencies, damping ratios, and total number of TMDs in the system. It is found that SAIVS MTMD is more effective than passive MTMD in reducing structural response, and SAIVS TMD is more efficient than SAIVS MTMD because the total SAIVS TMD mass oscillates exactly at the excitation frequency instead of distributing the mass among individual dampers. Both SAIVS TMD and SAIVS MTMD are found to be very robust against changes in the natural frequency of the main structure.

An approximate method to predict the second-order deflections and twist rotations is developed by Trahair in “Biaxial Bending and Torsion of Steel Equal Angle Section Beams.” The proposed method is then used to determine peak biaxial bending moments in such beams, leading eventually to the approximation of member capacities that also incorporate conditions of lateral buckling. Shaat and Fam present “Fiber-Element Model for Slender HSS Columns Retrofitted with Bonded High-Modulus Composites.” The model accounts for plasticity of steel, through-thickness residual stresses, geometric nonlinearity, imperfections arising from initial out-of-straightness, and the contribution of CFRP sheets. It is shown that CFRP effectiveness increases for columns with larger out-of-straightness deficiencies, higher slenderness ratios, and lower residual stresses. “Effects of Continuity Plate and Transverse Reinforcement on Cyclic Behavior of SRC Moment Connections” are reported by Chou and Uang. Continuity plates were eliminated, and two steel doubler plates were offset from the column web to enhance shear resistance in the first specimen. Sixty percent of the ACI-318 specified transverse reinforcement was provided in the joint region. In the second specimen, a steel jacket was provided to confine the joint region without transverse reinforcement, and continuity plates were extended from the column to the jacket. The results of full-scale tests indicate that both specimens were able to reach an interstory drift in excess of 4%.

The “Evaluation, Calibration and Verification of a Reinforced Concrete Beam-Column Joint Model” is presented by Mitra and Lowes. A formulation that builds on an existing model is proposed, wherein the shear stress-strain response of the joint core is developed by assuming joint shear to be transferred through a confined concrete strut. Modifications are also made to the original model to enable better simulation of the anchorage zone response. A comparison of simulated and observed response histories suggests that the enhanced model reasonably represents joint stiffness and strength parameters for a range of design parameters. A method of analysis based on shape functions approximating deformations is proposed by Dall’Asta, Ragni, and Zona in “Simplified Method for Failure Analysis of Concrete Beams Prestressed with External Tendons.” The method facilitates the study of the tendon stress increment and, consequently, the flexural strength of externally prestressed concrete beams. It also reduces the analysis of externally prestressed structures from a global structure problem to a simpler section problem. The formulation is verified by comparison with validated nonlinear finite-element simulations.

A fully automated procedure to determine global properties of full-scale wood panels is presented by Gsell et al. in “Cross Laminated Timber Plates: Evaluation and Verification of Homogenized Elastic Properties.” Experimental modal analysis is used to estimate resonant frequencies and mode shapes of the panels, and an analytical model is developed to estimate these parameters numerically. The shear moduli and in-plane stiffness are then established through a system identification procedure. It is shown that the global mechanical behavior of the specimen is accurately described using an orthotropic, homogenized, linear elastic material.

Murtagh, Basu, and Broderick propose “Gust Response Factor Methodology for Wind Turbine Tower Assemblies” for evaluating the along-wind response of wind turbine towers. A two degree of freedom reduced order model of the coupled tower-rotor system is developed, and the gust response factor (GRF) is obtained for both the tower tip displacement and base bending moment. Models in which the blade-tower interaction was ignored produced lower GRFs. Zhu et al. investigate the “Effect of Openings on Oriented Strand Board Webbed Wood I-Joists.” Finite-element models of the joists were validated with experimental results and then used to investigate the effect of opening size and location on joist behavior. An empirical relationship to estimate the load carrying capacity of joists with openings is derived.

Commenting on the paper “Explaining the Riddle of Tension Stiffening Models for Shear Panel Experiments” by Bentz, which appeared in the September 2005 issue of the Journal, Bischoff points out that the effects of concrete shrinkage have often been ignored in estimating the amount of tension stiffening observed in experiments. Restraint to shrinkage causes compression in the reinforcing bars while inducing tension in the concrete at the same time, leading to a reduction in the cracking load of the member and produces an offset in the bare bar response. The author concurs with the discusser on the issue but indicates that it is likely that the “well-aged” specimens considered in the study experienced fairly uniform shrinkage. Moreover the equations represent “average” results whereas shrinkage effects are implicitly included. On the relationship between bond and crack spacing, the author notes that the observed crack spacing in shear panel experiments is lower than expected because the formation of cracks is also controlled by other effects such as location of transverse reinforcement and other complex localized effects.

Aristizabal-Ochoa, J. D. (2007). “Tension and compression stability and second-order analyses of 3D multicolumn systems: Effects of shear deformations.” J. Eng. Mech., 133(1).

Dall’Asta, A., Ragni, L. and, Zona, A. (2007). “Analytical model for geometric and material nonlinear analysis of externally prestressed beams.” J. Eng. Mech., 133(1).

Guzda, M., Bhattacharya, B., and Mertz, D. R. (2007). “Probabilistic characterization of live load using visual counts and in-service strain monitoring.” J. Bridge Eng., 12(1).

Johnson, E. A., Baker, G. A., Spencer, B. F., and Fujino, Y. (2007). “Semiactive damping of stay cables.” J. Eng. Mech., 133(1).

Kayal, S. (2007). “Plastic rotation of an R.C.C. T-beam bridge under the combined influence of flexure and torsion.” J. Bridge Eng., 12(1).

Kayser, C. R., Swanson, J. A., and Linzell, D. G. (2007). “Fatigue resistance of HPS485W (70 W) continuous plate with punched holes.” J. Bridge Eng., 12(1).

Najm, H., Patel, R., and Nassif, H. (2007). “Evaluation of laminated circular elastomeric bearings.” J. Bridge Eng., 12(1).

Okui, Y., and Nagai, M. (2007). “Block FEM for time-dependent shear-lag behavior in two-I girder composite bridges.” J. Bridge Eng., 12(1).

Sahin, M., and Ozturk, M. (2007). “Uniform shear buildings under the effect of gravity loads.” J. Eng. Mech., 133(1).

Yang, J. N., Pan, S., and Lin, S. (2007). “Least-squares estimation with unknown excitations for damage identification of structures.” J. Eng. Mech., 133(1).

Ye, Z. Q., and Ma, G. W. (2007). “Effects of foam claddings for structure protection against blast loads.” J. Eng. Mech., 133(1).

Zhang, J., Li, C., Xu, F., and Yu, X. (2007). “Test and analysis for ultimate load carrying capacity of existing reinforced concrete arch ribs.” J. Bridge Eng., 12(1).