Search

Compensation of delay and dynamic response of servo-hydraulic actuators is critical for stability and accuracy of hybrid experimental and numerical simulations of seismic response of structures. In this study, current procedures for compensation of actuator delay are examined and improved procedures are proposed to minimize experimental errors. The new procedures require little or no a priori information about the behavior of the test specimen or the input excitation. First, a simple approach is introduced for rapid online estimation of system delay and actuator command gain, thus capturing the variability of system response through a simulation. Second, an extrapolation procedure for delay compensation, based on the same kinematics equations used in numerical integration procedures is examined. Simulations using the proposed procedures indicate a reduction in high-frequency noise in force measurements that can minimize the excitation of high-frequency modes. To further verify the effectiveness of the compensation procedures, the artificial energy added to a hybrid simulation as a result of actuator tracking errors is measured and used for demonstrating the improved accuracy in the simulations.

An approximate method is proposed for the dynamic analysis of torsionally coupled tall building structures by utilizing the properties of their uncoupled counterparts. An exact solution is first given for the particular case in which the lateral and torsional stiffness matrices are uncoupled by same transformation. The method is then applied to a wider class of structures where this condition is only approximately satisfied by reducing the dynamic coupling problem to an approximate two-degrees-of-freedom system. Simple formulae and graphical representations of dynamic magnification of static eccentricity are given. Two numerical examples illustrate the use of the proposed method, checking on its accuracy and comparing its results with seismic code provisions.

An efficient approximate hand method is proposed for the evaluation of the dynamic properties of asymmetric wall-frame structures. The approximation is based on a two-degree-of-freedom zeroth order solution of the coupled differential equations of motion. The restrictions on the structural geometry of the building imposed in a previous paper1 are relaxed and the accuracy of the approximation is made dependent on the similarity between the mode shapes of the uncoupled lateral and torsional systems.