Seismic loading tests of full-scale two-story steel building frames with self-centering braces and buckling-restrained braces

Abstract

A new steel dual-core self-centering brace (DC-SCB) has both re-centering and energy dissipation properties in seismic loading, reducing residual deformation of a frame structure with a buckling-restrained brace (BRB). Previous works showed that both DC-SCBs and BRBs perform satisfactorily in seismic loading, but study of a full-scale, multi-story steel frame with these two different braces in one test program is very limited. Three full-scale two-story, one-bay steel frame specimens, named as DC-SCBF, SBRBF and SMBF which had DC-SCBs, BRBs and a combination of DC-SCBs and BRBs, respectively, were cyclically tested. Multiple tests of the 9 m-wide, 7.54 m-high braced frame specimens were focused on: (1) validating the system response with DC-SCBs, BRBs and a combination of these two different braces, (2) studying the variation of the lateral stiffness, maximum force and energy distribution of the frames, and (3) discovering the failure and repair characteristics of the frames under seismic loading. Nonlinear time history analyses were conducted on the three prototype braced frames to obtain seismic demands for the test protocol. Theses two-story frame specimens performed satisfactorily up to an interstory drift of 2%, which was close to the mean value of the maximum interstory drift of the prototype frames under 20 Maximum Considered Earthquake (MCE) motions. No damage of the DC-SCB or BRB was observed, but a fracture of the steel beam flange near the joint of the beam web stiffener and gusset plate toe was observed due to low-cycle fatigue loading. In direct contradiction to brace component tests, the energy dissipation of the two-story frame specimen with DC-SCBs is higher than that with BRBs due to higher post-yield stiffness of the DC-SCB. The post-yield lateral stiffness of Specimen DC-SCBF is about 20% of its elastic lateral stiffness and 1.6–1.8 times that of Specimens SMBF and SBRBF. In addition to the energy dissipation, the higher post-yield stiffness is also a better way to reduce the maximum drift of the frame in earthquakes. Moreover, Specimen SMBF that adopts a combination of DC-SCB and BRB along the building height has intermediate lateral stiffness, residual deformation and energy dissipation among all frame specimens, verified as a potential seismic-resisting frame system.