Seismic behavior of composite beam connected to HSS column with large width-to-thickness ratio

This paper discusses out-of-plane deformations in a HSS (Hollow Structural Section) column connected to a composite beam. Width-to-thickness ratio of HSS column is an important parameter in the flexural deformation capacity of the connection. Beam web connection moment transfer efficiency in HSS column connection is poor and significantly less effective when compared to a connection with W-shape columns. This condition is more severe in the case of composite beam connected to thin walled HSS columns having large width-to-thickness ratio. In this research, the force flow pattern and ultimate flexural capacity of web connection are evaluated by considering main parameters affecting the out-of-plane deformations namely: width-to-thickness ratio of HSS column, height-to-thickness ratio of beam web, yield strength ratios of beam and column, height-to-width ratio of connection, slab strength, stud layout and geometry of weld access hole. Results from the analysis are utilized to illustrate the location of neutral axis and structural condition of web connection in different width-to-thickness ratios and different concrete slab strengths. Also, equations for evaluation of ultimate flexural capacity of web connection are derived; interaction curves of Moment-Axial force acting at the web are drawn. It was found that in the HSS column with large width-to-thickness ratio of 29, axial force subjected to the web connection results in significant reduction of web flexural capacity. Experimental tests showed that plastic rotation capacity of composite beam decreased to almost half of the capacity of bare steel beam. In order to improve seismic behavior, a gap was provided between concrete slab and column face. However, experimental tests revealed that the application of a gap between concrete slab and column face solely did not improve the rotation capacity. The Finite element study showed that despite the existence of a gap, headed studs contribute to the composite action and modification of stud layout is needed. Investigation about the contribution of studs located on the loaded beam and transverse beam has been conducted. Recommendations for seismic application of composite beam connected to HSS column with large width-to-thickness ratio have been presented.