An experimental program has been completed recently to evaluate the long-term performance of the seismic isolation bearings manufactured for the Foothill Communities Law and Justice Center. Two pairs of full-size bearings were tested — one was removed from the building approximately 12 years after installation, and the other pair was from the original set of 4 prototype bearings. This article summarizes the tests of the bearings removed from the building, which indicate that while there are minor differences from the original properties, the isolation system should be expected to perform as designed in the case of a strong earthquake.
This study develops an active control methodology for the AMD benchmark problem of Spencer, et al. (1997) based on dynamic output feedback controllers designed using an H1 based approach. Kalman lter estimators of the states of a reduced order model of the benchmark structure are coupled to static state feedback controller gains to develop the dynamic feedback controllers. A method is outlined for designing H1 feedback controller gains, and a comparison is made between the e ectiveness of H1 static output feedback and the dynamic acceleration feedback controllers. The results quantify the performance increase obtained with the additional complexity of the dynamic output feedback controllers compared to the static acceleration feedback controllers. Introduction For the AMD benchmark problem of Spencer, et al. (1997), controllers are designed using two H1 based approaches: one approach uses direct static output feedback of sensor measurements, and the second approach uses a dynamic output feedback controller that consists of static state feedback controller gains with a Kalman lter state estimator. The controllers considered in this study are designed by a continuous-time H1 controller approach, then discretized for simulation with the benchmark model. The controllers are developed from a state space design model of the form: _ x(t) = Ax(t) +Buu(t) +Bww(t) (1) z(t) = Czx(t) +Dzuu(t) +Dzww(t) (2) y(t) = Cyx(t) +Dyuu(t) +Dyww(t) (3) where x(t) is the state vector, u(t) is the vector of control inputs, w(t) is the vector of disturbance inputs, y(t) is the vector of sensor measurements, z(t) is the vector of regulated outputs, and A, Bu, Bw, Cz, Dzu, Dzw, Cy, Dyu, and Dyw are matrices of Assistant Professor, Stanford University, Dept. of Civil Engineering, Stanford, CA 94305. Research Assistant, Stanford University, Dept. of Civil Engineering, Stanford, CA 94305.
In this paper, both the methods of continuous sliding mode control (CSMC) and continuous sliding mode control with compensators (CSMC&C) have been applied to two benchmark structures, namely, a building model equipped with an active mass driver system, and a building model equipped with an active tendon system. The CSMC&C strategy is a modification of CSMC to facilitate the design of static output feedback controllers and to provide a systematic tuning of the control effort. Due to the structural identification scheme used in the benchmark problems, in which the state variables are fictitious, one cannot take the full advantages of static output feedback controllers. As a result, an observer is used in CSMC, whereas a low-pass filter is incorporated for each measurement in CSMC&C. The purpose of using low-pass filters in CSMC&C is to transform the benchmark problems into strictly proper systems. The main advantage of the CSMC&C method is that the on-line computational effort is reduced since the dimension of filters and compensator is much smaller than that of an observer. Simulation results based on the CSMC and CSMC&C methods are presented and compared with that of the LQG method. Robustness of stability and noise rejection for each controller design are also illustrated by examining the loop transfer function. Simulation results for the benchmark problems indicate that the control performances for LQG, CSMC and CSMC&C are quite comparable. © 1998 John Wiley & Sons, Ltd.
An energy based approacb has been used to investigate the seismic behavior of code-designed, asymmetric-plan systems. The presented results demonstrate that the total input energy is about the same whether the system plan is symmetric or asymmetric. Furthermore, elements on the flexible-side in asymmetric-plan systems are more vulnerable compared to the same elements in symmetric-plan systems. The stiff-side elements, on the other hand, are expected to suffer no more damage in asymmetric-plan systems. This observation correlates well with the damage observed during several earthquakes.
