Seismic performance of double-channel and double-HSS sections, special truss moment frame with buckling restrained braces, and long span Special Truss Moment Frame

Abstract

Until recently, all special truss moment frame (STMF) experimental research was done on only double angle STMFs. In order to satisfy the code seismic drift limitation, especially for mid-rise and tall multistory buildings, a large column section is needed, when double angle sections are used. However, heavy chord members can be used in this instance. Due to configuration of STMFs, the chord members in the special segment of an STMF experience higher rotational demand than the story drift. As a result, there is a need to verify large rotational capacity of other heavy steel shapes. Recent analytical investigation and experimental investigation at component level showed that double channel sections could be used in STMFs. However, to maintain large rotational capacity of double channel sections, lateral support was needed near plastic hinge region to prevent lateral torsional buckling (LTB). This research investigated ways to maintain double channel rotational capacity without having to provide lateral support and viability of using double HSS sections which are not susceptible to LTB in STMFs. A new connection detail was tested and the results showed that lateral torsional buckling was eliminated. Results on double HSS sections showed that it could maintain strength at very high rotation. Other than verifying large rotational capacity of double channel and double HSS sections, this research also introduced incorporating buckling-restrained braces to provide additional stiffness and strength to full scale STMF subassemblage test. Moreover, the possibility of extending span the length of STMFs to 90 ft was explored. When a span length of STMF is very long, its stiffness could be compromise. In addition, induced axial force due to gravity loading could be significant. The effect of axial load on ductility of double channel sections was studied. Seismic performance of 90 ft span STMFs was evaluated and design recommendation are proposed.