Cyclic Loading Performance of Full-Scale Special Truss Moment Frames With Innovative Details for High Seismic Activity Areas

Abstract eng:
Special truss moment frames (STMFs) represent a steel structural framing system which is able to provide long bay width and high lateral stiffness due to the deep truss girders. Moreover, the open webs of the truss girders can accommodate mechanical and electrical ducts which are functionally desirable. When subjected to a strong earthquake, an STMF dissipates energy through a ductile special segment located near the mid-span of the truss girder. This special segment acts like a structural fuse because the chord members and diagonal members in the special segment are designed to behave inelastically, while other members outside of the special segment are designed to remain elastic. Prior experiments and analyses done on STMFs using double-angle sections as truss members led to the current design procedures in the 2010 and 2016 Draft version of the American Institute of Steel Construction’s AISC Seismic Provisions for Structural Steel Buildings. Due to insufficient capacities of angle sections for buildings under severe earthquakes, there is a strong need for using heavier structural steel sections as STMF members. This paper presents an overview of the test results of a full-scale allVierendeel panel STMF enhanced by short buckling-restrained braces (BRBs). The specimens used innovative details to eliminate the lateral-torsional buckling of the chord members, thereby enhancing the rotational capacity of the special segments, as well as incorporated reduced beam section (RBS) of 2C310×30.8 to reduce strength demand of the members outside of the special segment. The test results showed that BRBs could be safely used to enhance both strength and stiffness of the STMF. By using the short BRBs, structural redundancy of STMF increases and when the BRBs are damaged under moderate earthquake, they can easily be replaced. Even after BRBs failed in tension, STMF could still maintain its strength at large story drift because the broken yielding cores reengaged in compression and provided additional resistance.

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