Editor’s Note

The issue opens with Kasalanati and Constantinou’s paper on “Testing and Modeling of Prestressed Isolators.” A mechanism that utilizes prestressing forces to prevent uplift in isolation bearings is proposed, and a theory for modeling three types of isolators, namely, flat sliders, spherically shaped sliding bearings, and elastomeric bearings, is described and validated with experimental testing. The seismic behavior of a quarter-scale, three-story steel frame is investigated by Wongprasert and Symans in “Experimental Evaluation of Adaptive Elastomeric Base-Isolated Structures Using Variable-Orifice Fluid Dampers.” In addition to experimental tests to validate the variable orifice dampers, the writers develop an analytical model to simulate the response of the isolated structure.

An analytical model for “Shear Analysis and Design of Ductile Steel Plate Walls” is presented by Sabouri-Ghomi, Ventura and Kharrazi. The effectiveness of the approach is demonstrated by comparing predicted response with available experimental data. The effectiveness of using magnetorheological (MR) dampers to prevent whipping effects caused by a sudden change in lateral stiffness in building structures is experimentally investigated by Xu et al. in “Semiactive Seismic Response Control of Buildings with Podium Structure.” Pourzeynali and Datta present an analytical study of “Semiactive Fuzzy Logic Control of Suspension Bridge Flutter.” The proposed tuned mass damper system using variable damping and fuzzy logic control is shown to be effective in controlling flutter in suspension bridges.

The next set of three papers deals with fatigue behavior of structural steel components. A two-part paper by Liu, Liang, and Lee examine the “Low-Cycle Bending-Fatigue Strength of Steel Bars Under Random Excitation.” The failure mechanism of A36 structural steel is shown to depend on the orientation angle of the grain. Based on the results of experimental tests, a damage model is proposed for random amplitude reversals. Xiao and Yamada report on experimental testing to investigate the “Fatigue Strength of Intersecting Attachments.” Results indicate that the fatigue strength of T-type attachments is comparable to that of the single longitudinal attachment, whereas, H-type attachments exhibit a capacity between those of the single longitudinal and transverse attachments.

Wang and Helwig study “Critical Imperfections for Beam Bracing Systems” and make recommendations for selecting the critical imperfection shape that maximizes the stability forces for beam bracing systems. An exact formula is derived by Der Kiureghian and Sackman for the “Tangent Geometric Stiffness of Inclined Cables under Self-Weight.” A comparison with the approximate formula by Ernst indicates that the approximations deteriorate with increasing cable slack and inclination. “Damage Mechanics Modelling of Nonlinear Seismic Behavior of Concrete Structures” by Legeron, Paultre, and Mazars presents a simplified finite-element analysis program using multilayer elements. The approach is validated with monotonic and cyclic experiments on normal and high-strength concrete beams and pseudo-dynamic tests on bridge piers.

A finite-element procedure is proposed by Katkhuda, Martinez, and Haldar to identify defects in existing structures in their paper, “Health Assessment at Local Level with Unknown Input Excitation.” It is demonstrated through examples that the proposed algorithm can be used in nondestructive evaluation for assessment of existing structures with minimal disruption. Lu, Gu, and Guan utilize Monte Carlo simulations in “Probabilistic Drift Limits and Performance Evaluation of RC Columns” to establish three performance levels. Fragility curves are developed to assist in evaluating the performance reliability of different column designs.

Two technical notes are also included in this issue. Berton and Bolander propose the use of special lever mechanisms as an “Amplification System for Supplemental Damping Devices in Seismic Applications.” Laboratory tests on a scaled version of the displacement amplification device to validate the concept are presented in the paper. The second technical note titled “On the Validity of Wind Load Distribution Based on HFFB Measurements,” Chen and Kareem contend that the accuracy of high frequency force balance (HFFB) based identification of spatiotemporally varying wind loads on buildings depends primarily on the assumed wind loading model.

The issue concludes with a discussion by Peterka and Esterday on a paper by Simiu et al. that appeared in the April 2003 issue of the Journal. The discussers clarify issues related to the legitimacy of including stations with different meteorology in so-called superstations and related concerns that were raised by Simiu et al. with reference to an earlier publication by the discussers. The authors bring closure to the subject by responding to the questions posed by the discussers and noting that a debate on the original work by Peterka and Shahid that contributed to the ASCE 7 Standard is beneficial to the engineering community.

The next discussion is on Lowes and Altoonash’s paper on RC beam-column joints that appeared in the December 2003 issue. LaFave and Shin question the validity of the model for nonductile joints. The authors agree that it is important to establish the range of joint design parameters for which the application of MCFT is applicable. The final discussion item is by Rajasekaran and Nalinaa on a paper by Zararis on shear compression failure in RC deep beams, which appeared in the April 2003 issue of the Journal. The discussers suggest the use of sequential learning neural network (SLNN) as an alternative approach to solve the problem. The discussers point out that the limitation of such a method is that it relies on the accuracy of experimental data.

Chen, H. C., and Liew, J. Y. R. (2005). “Explosion and fire analysis of steel frames using mixed element approach.” J. Eng. Mech., 131(6).

Okelo, R., and Yuan, R. L. (2005). “Bond strength of FRP rebars in normal strength concrete.” J. Compos. Constr., 9(3).

Farhey, D. N. (2005). “Long-term performance monitoring of the Tech 21 all-composite bridge.” J. Compos. Constr., 9(3).

El Maaddawy, T., Soudki, K., and Topper, T. (2005). “Computer-based mathematical model for performance prediction of corroded beams repaired with FRPs.” J. Compos. Constr., 9(3).

Chong, K. P., and Larsen-Basse, J. (2005). “Challenges in mechanics and materials research in the twenty-first century.” J. Mater. Civ. Eng., 17(3).

William, K., Rhee, I., and Xi, Y. (2005). “Thermal degradation of heterogeneous concrete materials.” J. Mater. Civ. Eng., 17(3).

Note: The June 2005 issue of the J. Eng. Mech. includes a collection of papers on advances in the stability of framed structures.