Dr. Satish Nagarajaiah
Professor of Civil and Mechanical Engineering
Rice University, Houston, TX

Smart Structures Based on Variable Stiffness and Damping Systems


This seminar presents a new and innovative smart or semi-active variable stiffness tuned mass damper (STMD), which is based on a novel semi-active variable stiffness control (SAIVS) system developed at Rice University. STMD system has the distinct advantage of continuously retuning its frequency in real time; hence, the system is robust to changes in building stiffness and damping. In comparison, the passive tuned mass damper (TMD) can only be tuned to a fixed frequency. Nonlinear analytical models of the STMD and structural systems are developed. The frequency tuning of the STMD is achieved using newly developed control algorithms based on time-frequency techniques (such as instantaneous frequency and Hilbert transform, short time Fourier transform, and Empirical Mode Decomposition). It is shown that the STMD can reduce the structural response substantially, when compared to the uncontrolled case; it can reduce the response further when compared to the case with TMD. Additionally, it is shown the STMD reduces response even when the building stiffness changes and is robust. It is also shown that STMD can reduce the response similar to an active tuned mass damper.

Semiactive control includes (1) independently variable stiffness control, (2) independently variable damping control, or (3) combined variable stiffness and damping control. Most studies to date have considered systems with semiactive magnetorheological (MR) dampers and shown their effectiveness in reducing the response of structures due to earthquakes. In this seminar, systems which can independently vary both stiffness (SAIVS) and damping (MR damper) are presented. The effect of combined control in reducing the response of sliding isolated structures due to near fault earthquakes is discussed. Nonlinear response spectra and time-histories are presented to show the reduction in response obtained.

Short Biography

Professor Satish Nagarajaiah holds a joint appointment in the Civil and Mechanical engineering departments at Rice University, where he serves as the associate chairperson. He obtained his Ph.D. from University at Buffalo, in 1990, and performed post-doctoral work from 1990 to 93. His teaching and research interests are in the areas of dynamic systems and control, smart structures and sensors, structural health monitoring. His current research focuses on intelligent systems in projects funded by NASA and NSF. He has received numerous awards including the National Science Foundation CAREER award in 1998. He currently advises two postdoctoral researchers, six Ph.D. students, and one M.S. student.


Friday, April 28th, 2006


3:00 - 4:30 PM EST

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Seminar sponsored by MCEER Networking and Education Programs, MCEER SLC and hosted by the Department of Civil, Structural and Environmental Engineering and the EERI Student Chapter at UB.


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