Publications

Abstract Many branches of engineering, mathematics, and sciences, have relied on benchmark problems as a standard means to compare different solution techniques. Since 1996, the ASCE Structural Control and Monitoring Committee and Task Group on Benchmark Problems, the U.S. Panel on structural control, and IASCM have developed a series of benchmark control problems that offer a set of carefully modeled real-world structures in which different control strategies can be implemented, evaluated, and compared using a common set of performance indices. First-, second- and third-generation benchmark problems focusing on the response control of seismic and wind-excited buildings, and seismically excited long-span cable-stayed bridges have been developed and evaluated. The U.S. Panel on structural control and monitoring (currently chaired by Professor Satish Nagarajaiah, Rice University, Houston, TX), IASCM, and the ASCE structural control and monitoring committee have developed a new benchmark study to compare control strategies designed for a base-isolated building subjected to strong near-fault pulse-like ground motions. The special issue on phase I smart base-isolated building benchmark problem with a linear isolation system was successfully completed and published. This special issue focuses on the phase II smart base-isolated building benchmark problem with nonlinear isolation systems—friction or elastomeric system. Copyright © 2008 John Wiley & Sons, Ltd.

This paper proposes a novel lossy data compression scheme for structural seismic responses based on principled (truncated) independent component analysis (PICA). It is first shown that independent component analysis (ICA) is able to transform a multivariate data set into a sparse representation space where is optimal for coding and compression, such that both the intradependencies and interdependencies (i.e., redundant information) between the multichannel data are removed for efficient data compression. Two examples are presented to demonstrate the compression performance of PICA, using the real-measured structural seismic responses from the 1994 Northridge earthquake, of the Fire Command Control (FCC) building and the USC hospital building, respectively. It is compared with the popular wavelet transform coding technique, which is only able to handle single-channel data separately. Results show that PICA achieves dramatically higher compression ratio (CR) than the wavelet method while retaining excellent reconstruction accuracy. It is also shown that PICA slightly outperforms the (principled) principal component analysis (PCA) method—which used to be considered optimal multivariate data compression scheme—with respect to both CR and reconstruction accuracy. Equipped with the FastICA algorithm that enjoys a cubic convergence rate, PICA has potential for rapid and reliable data transfer, communication (e.g., multihop wireless sensor network), storage, and retrieval in online or post-disaster (e.g., earthquake) monitoring and assessment applications of civil infrastructures.

This paper presents a new variable stiffness control system, which can switch the stiffness continuously and smoothly. the new and innovative semi-active variable stiffness control (SAIVS) device and tests performed to study the effectiveness of the device are presented. A new control algorithm based on instantaneous frequency estimation using Hilbert transform is developed and implemented in real time digital signal processing system and controller. Shake table test results of a single degree of freedom system with SAIVS device is presented.

Complicated temperature fields and crossing high-speed trains offer new challenges for monitoring girder deflections in operating railway bridges. Behavior analyses and early warning of girder deflections are necessary for the diurnal operation of bridge structures. Regarding the Nanjing Dashengguan Yangtze River Bridge, the present paper identifies the temperature-induced/train-induced deflections of the bridge girder from deflection data obtained from the wavelet transform. The principal components of the bridge temperature field are obtained to verify the temperature sensitivity of the girder deflection. The effect of the temperature-induced girder deformation on train-induced girder deflections is analyzed using the train-bridge dynamic model. The statistical laws of the downward and upward of train-induced girder deflections are described using the t location-scale distribution. Based on the mutual updating of monitoring data and numerical model, the behaviors of the temperature-induced/train-induced deflections of the bridge girder can be captured accurately, and the warning threshold of girder deflections under the coupling effects of temperature and trains is determined rapidly. The results demonstrated that the influence of the temperature-induced girder deformation on the train-induced girder deflection is relatively small when compared with the train-induced girder deflection itself, with the increasing amplitude being no more than 3%. A real-time early warning of girder deflections for the long-span railway bridge can be conducted to indicate the abnormal changes in girder deflection less than 10 s, which is likely due to the deterioration of track irregularity on the bridge or damaged bridge components.

A family of smart tuned mass dampers (STMDs) with variable frequency and damping properties is analyzed under harmonic excitations and ground motions. Two types of STMDs are studied: one is realized by a semi-active independently variable stiffness (SAIVS) device and the other is realized by a pendulum with an adjustable length. Based on the feedback signal, the angle of the SAIVS device or the length of the pendulum is adjusted by using a servomotor such that the frequency of the STMD matches the dominant excitation frequency in real-time. Closed-form solutions are derived for the two types of STMDs under harmonic excitations and ground motions. Results indicate that a small damping ratio (zero damping is the best theoretically) and an appropriate mass ratio can produce significant reduction when compared to the case with no tuned mass damper. Experiments are conducted to verify the theoretical result of the smart pendulum TMD (SPTMD). Frequency tuning of the SPTMD is implemented through tracking and analyzing the signal of the excitation using a short time Fourier transformation (STFT) based control algorithm. It is found that the theoretical model can predict the structural responses well. Both the SAIVS STMD and the SPTMD can significantly attenuate the structural responses and outperform the conventional passive TMDs.