Evaluation of a substructured soft-real time hybrid test for performing seismic analysis of complex structural systems

The hybrid test method is a relatively recently developed dynamic testing technique that uses numerical modelling combined with simultaneous physical testing. The concept of substructuring allows the critical or highly nonlinear part of the structure that is difficult to numerically model with accuracy to be physically tested whilst the remainder of the structure, that has a more predictable response, is numerically modelled. In this paper, a substructured soft-real time hybrid test is evaluated as an accurate means of performing seismic tests of complex structures. The structure analysed is a three-storey, two-by-one bay concentrically braced frame (CBF) steel structure subjected to seismic excitation. A ground storey braced frame substructure whose response is critical to the overall response of the structure is tested, whilst the remainder of the structure is numerically modelled. OpenSees is used for numerical modelling and OpenFresco is used for the communication between the test equipment and numerical model. A novel approach using OpenFresco to define the complex numerical substructure of an X-braced frame within a hybrid test is also presented. The results of the hybrid tests are compared to purely numerical models using OpenSees and a simulated test using a combination of OpenSees and OpenFresco. The comparative results indicate that the test method provides an accurate and cost effective procedure for performing full scale seismic tests of complex structural systems.

► We performed 16 hybrid tests on steel concentrically braced frames. Hybrid tests comprise of physically testing the critical part of the structure (physical substructure) whilst numerically modelling the remainder of the structure (numerical substructure).
► A novel approach of performing hybrid tests using OpenFresco has been developed where the lateral stiffness of the X-braced frame physical substructure is represented in OpenFresco using two experimental beam-column elements.
► Comparison of test results and numerical models has shown the novel approach using OpenFresco to be a successful generic framework to perform hybrid tests of a complex structural system at full scale.