Effective force testing: A method of seismic simulation for structural testing

This paper presents a test method for real-time earthquake simulation studies of large scale test structures. The method, effective force testing (EFT), is based on a force control algorithm. For systems that can be modeled as a series of lumped masses (e.g., frame structures where masses are assumed lumped at the floor levels), the EFT forces are known a priori for any acceleration record. As opposed to the pseudodynamic test method (a displacement-based control procedure), there is no computational time required for the EFT method in determining the required force signal; it is known prior to the test once the structural mass and ground acceleration record to be simulated are determined. Research has been conducted on a single-degree-of-freedom system at the University of Minnesota to investigate the potential of the EFT method. A direct application of the method was found ineffective because the actuator was unable to apply force at the natural frequency of the structure owing to actuator/control/structure interaction. However, numerical simulations and experimental implementation indicated that an additional velocity feedback loop incorporated into the control system can overcome this problem while maintaining the ability to do real-time testing.