Seismic Performance of Buckling-Restrained Braces Subjected to Subduction Interface Earthquake Demands

Abstract

Abstract Five full-scale buckling-restrained brace (BRB) specimens, part of the second story of a 5-story steel buckling-restrained braced frame (BRBF), were tested experimentally to investigate their seismic response under demands imposed by long-distance subduction interface earthquakes anticipated in the Pacific Northwest. Two of the specimens were previously tested as part of a past study and strain-aged for 2 years and 8 months, and the other three specimens were new. Two of the new specimens were each subjected to a symmetrically increasing loading protocol, including the current American Institute of Steel Construction Seismic Provisions for Structural Steel Buildings, AISC 341, standard loading protocol for the first specimen, and a subduction loading protocol for the second. The resulting envelope curves suggest consistent postyield slopes between both protocols, with overstrength forces at the design story drift differing by less than 2%. The remaining three specimens, one new and two previously tested and strain-aged, were subjected to direct subduction earthquake deformation histories obtained from dynamic analyses of the selected braced frame subjected to historical subduction interface earthquakes. Two of the specimens resisted imposed strains that were 189% and 264% greater than the strain corresponding to brace deformation at the design story drift. Evaluating low-cycle fatigue demonstrated that all three BRBs subjected to direct subduction earthquake deformation histories contained ample residual capacity, even after resisting multiple earthquake deformations. When comparing the envelope curves of the two specimens tested under symmetric loading protocols with those subjected to direct earthquake loading, the results indicated that symmetric protocols generally developed sufficient overstrength to capture the expected brace strength under earthquake demands. Finally, strain-aging effects were evaluated by comparing the response of a new specimen and a previously tested specimen under direct earthquake deformations, which exhibited a 12% increase in tensile force and 17% increase in compression force.