Role of Control-Structure Interaction in Protective System Design

Most of the current research in the field of structural control for mitigation of responses due to environmental loads neglects the effects of control-structure interaction in the analysis and design. The importance of including control-structure interaction when modeling a control system is discussed herein. A specific model for hydraulic actuators typical of those used in many protective systems is developed, and experimental verification of this model is given. Examples are provided which employ seismically excited structures configured with active bracing, active tendon, and active mass driver systems. These examples show that accounting for control-structure interaction and actuator dynamics can significantly improve the performance and robustness of a protective system. Introduction The concept of structural control for civil engineering applications originated in the early 70’s (Yao, 1972). In the two decades since, much progress has been made toward exploiting the potential benefits offered by control for protection of structures against environmental loads such as strong earthquakes and high winds (e.g., Soong, 1990; Housner and Masri, 1990, 1993; ATC-17, 1993). Nearly all of the current literature on control of civil engineering structures does not directly account for control-structure interaction and actuator/sensor dynamics in the analysis and design of protective systems. Unmodeled control-structure interaction (CSI) effects can severely limit both the performance and robustness of protective systems. This is true for both active and semi-active systems. To study effectively the control-structure interaction problem, one must have good models for the dynamics of the associated actuators. This paper presents a general framework within which one can study the effect of control-structure interaction. Specific models are developed for hydraulic actuators typical of those used in many active structural control situations. A natural velocity feedback link is shown to exist, which tightly couples the dynamic characteristics of a hydraulic actuator to the dynamics of the structure to which it is attached. Neglecting this feedback interaction can produce poor, or perhaps catastrophic, performance of the controlled system due to the unmodeled or mismodeled dynamics of the actuator-structure interaction. In addition, the time lag in generation of control forces is accommodated through appropriate modeling of the actuator and the associated CSI. Experimental verification of the main concepts is presented. The implications on protective system design are illustrated through examples of seismically excited structures. Active bracing, active tendon and active mass driver (AMD) systems are considered. 1. Doctoral Candidate and Graduate Research Assistant, Department of Civil Engineering and Geological Sciences, University of Notre Dame, Notre Dame, IN 46556. 2. Associate Professor, Department of Civil Engineering and Geological Sciences, University of Notre Dame, Notre Dame, IN 46556. 3. Doctoral Candidate and Graduate Research Assistant, Department of Electrical Engineering, University of Notre Dame, Notre Dame, IN 46556. 4. Freimann Professor, Department of Electrical Engineering, University of Notre Dame, Notre Dame, IN 46556. Published in the ASCE Journal of Engineering Mechanics, Vol. 121, No. 2, Feb. 1995 pp. 322–338.