Impact of loading rate during hybrid simulation on seismic response of steel structures

This study investigates the influence of loading rates on the seismic response of steel structures. A series of coupon tests under typical earthquake-induced loading rates are carried out. In addition to the conventional monotonic tension test, the specimens are also tested under a discontinuous loading protocol that is analogous to the ramp-and-hold scheme employed in the pseudo-dynamic hybrid simulations. The test results are used to develop a uniaxial steel material model to account for the strain rate effect and stress relaxation. The material model facilitates the reuse of existing steel hysteresis models and can be used to model different structural components, such as columns, beams, braces, etc. The material model is then used for a parametric study to evaluate the impact of various loading rates on the global seismic response of a single degree of freedom structural system with different structural periods, and types and intensities of ground motions. It is found that the impact of loading rates is more significant for structures with a period of 0.5 s or less and it thus requires a fast control of the physical specimen in pseudo-dynamic hybrid testing. In addition, the material model is applied to a five-storey buckling restrained braced frame (BRBF) building with a structural period of 1.2 s. It is found that the earthquake-induced loading rates have a minor impact on the global response of the structure.