Seismic Hybrid Simulation of Stiff Structures: Overview and Current Advances

Advances in the area of structural testing have in recent years led to hybrid simulation, that is, the advanced structural experimental method that encompasses the traditional pseudodynamic testing method and relies on substructuring to offer the advantage of combining the actual experimental testing of selected parts of the structure to the numerical treatment of the rest. The experimental part usually involves simplified test setups and structural elements with few degrees of freedom. Thus, issues of cross-coupling present in testing MDOF structures have not been treated adequately so far. In addition, it has been realized that when it comes to testing very stiff structures, in which the above phenomena are accentuated, further problems arise in relation to the quality of actuator control (accuracy of imposed displacements and stability of the test process). Few studies have focused on these issues, thus necessitating more work in the future. The present study provides an overview of the approaches that have been adopted so far, reports on recent advancements, and raises the points in which more research is needed. 1. Introduction Extensive research and application of the pseudodynamic testing method in the 35 years that followed its inception, the “computer-actuator online testing method” [1, 2], have not only established it as one of the “standard” methods for seismic testing, but its application has also been extended towards new areas. By leveraging equipment commonly found at structural laboratories, the method has proven very competitive against costly shaking table testing, especially regarding the simulation of full-scale structures that respond in the nonlinear regime. With the exception, maybe, of its application to testing rate-dependent materials and distributed-mass systems, many of its initial weaknesses have been successfully treated: implicit or explicit/implicit methods for the integration of the equation of motion in time are now available, experimental errors have been minimized/compensated thanks to the deployment of high accuracy sensors or compensation techniques, and the staggered, ramp-hold-type, application of target displacements that introduced force-relaxation issues has been substituted by the continuous movement of the actuators (continuous pseudodynamic testing method). Furthermore, the extension of the method based on the concept of substructuring (i.e., the discretization of selected parts of the structure under test into actively interacting physical and numerical models (substructures)) forming a, so-called, “hybrid