Full-Scale Experimental Validation of Standardized Seismic-Resistant Cast Steel Brace Connectors

Abstract eng:
Although concentrically braced frames are an efficient and popular choice for the lateral force resisting systems of mid- to low-rise steel frames, their bracing connections may be prone to premature failure unless complex design and fabrication procedures are undertaken. Frames utilizing Hollow Structural Section (HSS) braces, slotted to receive a concentric welded gusset plate, are particularly susceptible to connection fracture due to stress concentrations arising from the shear lag phenomenon at the net-section. To address this issue, a cast steel connector was developed at the University of Toronto that provides a bolted connection between a circular hollow section (CHS) brace and a typical corner gusset plate. Unlike standard, fabricated, slotted-tube type connections, the cast connector is designed such that shear lag in the brace member is virtually eliminated. Thus, there is no need for cumbersome reinforcing plates in the connection region. The connector was designed using solid modeling software and finite element analysis, and cast using ASTM A958 grade steel, which is very similar to most wrought grades. This paper presents the results of a series of full-scale brace tests in which four moderately slender, compact, cold-formed CHS brace assemblies were cyclically loaded to failure. Each of the brace assemblies employed a different size of CHS and cast steel connector, with the latter in turn bolted to a typical corner gusset plate. Each of the tests followed the buckling restrained brace protocol specified in the American Institute of Steel Construction (AISC) Seismic Provisions. All of the braces survived several cycles beyond the protocol and failed in tension at the center of the brace. In each test the cast steel connectors showed no sign of yielding, illustrating that the use of a cast steel connector is a viable means of connecting CHS brace members for seismic applications.

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