Seismic resistant braced frame structures with shape memory alloy-based self-centering damping device

This article deals with seismic resistant braced frame structures with a special type of bracing element termed self-centering friction damping brace (SFDB). The SFDB provides a passive form of energy dissipation with its core re-centering component made of stranded superelastic shape memory alloy (SMA) wires while enhanced energy dissipation mechanism is provided through friction. Superelastic Nitinol is selected as the SMA material for SFDB because of its superb superelastic property and excellent fatigue life. The mechanical property of superelastic Nitinol wires was experimentally investigated through a series of uniaxial cyclic tests. The fatigue life and the effect of loading rate and ambient temperature are studied as a part of the experimental program. Three types of constitutive models for superelastic SMAs with increasing complexity and modeling details are discussed. Based on the calibrated constitutive model for superelastic Nitinol wires, analytical model for SFDB has been developed to simulate the unique flag-shaped hysteresis of SFDB. The seismic performance of SFDB frames is evaluated through nonlinear pushover and time history analysis of two prototype buildings-a 3-story and a 6-story concentrically braced frames, at different seismic intensity levels. A displacement-based design procedure for SFDB frame is also presented, in which SFDBs are proportioned based on the target performance level under design basis earthquakes. The simulation results demonstrate that SFDB frame has a few desirable performance characteristics such as minimal residual drift after frequent and design basis earthquakes due to its self-centering capability. SFDB frame has the potential to withstand several design basis earthquakes without the need for repair or replacement of SFDB if properly designed.