Quasi-static cyclic tests on a half-scaled two-storey steel frame equipped with Crescent Shaped Braces

This paper presents the first main results of quasi-static cyclic tests performed on a half-scaled two-storey one-bay steel pendular frame equipped with Crescent Shaped Braces (CSBs). The CSB is a yielding steel bracing element characterized by a boomerang-like shape, designed to provide the structure with an optimal combination of lateral stiffness, strength, ductility capacity and hysteretic dissipation, thus capable of meeting multiple seismic performance objectives within the context of Performance Based Seismic Design. In previous research studies, the behaviour of single CSBs under cyclic loads was analytically, numerically, and experimentally investigated through tests conducted on 1:6 scaled specimens. These results verified the potential capabilities of the device. As a further step of the experimental validation, a set of tests have been designed to evaluate the performances of CSBs when inserted into realistic frame structures. A two-storey prototype structure has been designed to meet selected seismic performance objectives, which could not be achieved with traditional diagonal braces. From that, a single-bay two-storey frame, representative of one braced frame of the whole structure, has been designed, detailed, and manufactured (half-scaled) for the experimental tests. For a full assessment of the behaviour of the braced frame, two configurations have been designed and tested. This paper presents the results of the test performed on the first configuration with one CSB device placed at the first storey only. The attention has been mainly focused on the global force-displacement response and the contribution of the connection plates, energy dissipation capacities and local strains around the knee-point region of the CSB. The results show that the CSB behaves following the theoretical predictions, while the connection plates provide a non-negligible contribution in the whole response of the system that should be properly accounted for in the design phase.