Vol. 4, No. 5, 2009

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Evolutionary control of structurally damaged steel buildings using an optimal state transition formulation

Thomas L. Attard and Robin E. Dansby

Vol. 4 (2009), No. 5, 855–886

An evolutionary gain formulation is proposed for minimizing the performance damage index of steel buildings subjected to earthquake forces. The gain formulation herein is used to develop the evolutionary control law of a control algorithm applied to inelastic systems. The optimal evolutionary gain is subsequently used to control building damages by satisfying desired performance objectives per time step “as needed”. The performance objectives are defined for various “damage-safe” and elastic demands. When the structure responds in the post-yield (inelastic) state, the material is assumed to follow a kinematic rule for strain hardening, which consequently may redefine the performance objective window at each unload/reload response state (cyclic control).

A control nonlinear time-history analysis program, dubbed CONON, was developed to simulate the stress-strain responses of structural members and to compute the optimal control forces per time step. The minimization of the cost function is independent of weighing matrices, thus alleviating cumbersome calculations that also lack physical description. Instead, an iterative Riccati matrix is computed per time step and is used to generate the evolutionary gain for the system leading to an appropriate evolution of the state transition between time steps. The calculated control responses are compared to uncontrolled responses. The results are also compared using various methods of gain calculation by examining the force-deflection hysteresis plots, the strain energy dissipation in the structural members, and the member accelerations of a steel frame. The proposed optimal system shows an excellent capability to control the desired target responses and meet acceptable performance objectives.

evolutionary structural dynamics, optimal control, evolutionary gain, plastic analysis, inelastic structures
Received: 19 January 2009
Revised: 16 May 2009
Accepted: 16 May 2009
Published: 5 September 2009
Thomas L. Attard
Department of Civil and Environmental Engineering
The University of Tennessee
113 Perkins Hall
Knoxville, TN 37996-2010
United States
Robin E. Dansby
California State University, Fresno
Department of Civil and Geomatics Engineering
M/S EE94
2320 E. San Ramon Avenue
Fresno, CA 93740-8030
United States