9424501 Udwadi This project will conduct theoretical and experimental studies to investigate the effects of time delays on the control of structural systems subjected to strong earthquake ground shaking. Both collocated as well as noncollocated control configurations will be considered. A general control methodology and guide lines will be developed. Stability conditions for vanishingly small gains, in the presence of time delays, when actuator and sensor are collocated, will be found for (a)undamped, (b) classically damped, and (c)nonclassically damned structural systems. The time delays which cause instability for collocated feedback control will be utilized to achieve infinitesimal gains stability for noncollocated feedback control systems. All analytical results will be applied to a simple five degree-of-freedom system for numerical verifications. This study will help understand the effects of small time delays, which are inevitable in the feedback loop, on the stability of the closed loop control systems. The results will have immediate and direct application to the robust control of a wide variety of structural and mechanical systems in dynamic environments, especially in the suppression of vibrations generated by earthquake ground shaking. ***
