Robustness against Time Delay and Control Force Capacity for Torsionally Irregular Active Controlled Structures

In active control of seismic structures, force capacity and time delay of the actuators are generally a restriction in the performance because of using high control forces for big mechanical systems like buildings. Although, a time delay value and a control force limit are considered in the tuning of the controllers, these factors may change according to physical conditions. For that reason, robustness against time delay and control force capacity is investigated for active controlled torsionally irregular structures in this study. The numerical example is a single story torsionally irregular structure controlled with active tendons using Proportional– Integral–Derivative (PID) type controllers. The tuning of PID controller parameters were done by using a numerical algorithm which scans the combination of three different controller parameters such as proportional gain, integral time and derivation time. Time delay is considered as 20 ms in the tuning process. Velocity at the critical direction was taken as error signal. Torsionally irregular shear building is under the effects of bidirectional earthquake excitation in horizontal directions. It has three degrees of freedom for each story including lateral displacement at two directions and rotation at the center of the mass. The primary aim is to reduce the responses of the structure in critical direction. Thus, torsional effects are also reduced. The robustness of active control systems was investigated for time delay values between 0 and 60 ms. The maximum control force was limited between 500 N and 6000N. Three different cases of active tendon orientation were considered and responses were investigated under Northridge-Sylmar record. Up to 50 ms time delay, the increase of control force limit has nearly linear effect on maximum displacements in critical direction (x). In the other direction (y) and rotational direction, a major performance lost is not seen if the control force limit is more than 1000 N. For 50 ms time delay and Case 3 (The best case in performance and the structure is controlled from all four sides.), a critical performance lost is seen for rotational effects for maximum control force limit more than 2000 N although reduction of displacements in x direction are not so affected. For 60 ms time delay, all cases are affected in rotational direction. Also, the displacements in x direction are affected after 3500 N force limit for Case 3. As a conclusion, torsional effects are more pronounced than lateral displacements by the increase of the time delay of active control systems. Key-Words: -Irregular Structures, Active Tendon Control, Robustness, Time Delay, PID controller, Earthquake