Moment-rotation model for blind-bolted flush end-plate connections in composite frame structures

Abstract

This paper develops both a three-parameter power model and a Ramberg-Osgood model for quantifying the moment - rotation characteristics of a blind-bolted flush end-plate system that connects a composite beam to a concrete-filled steel tubular (CFST) column in a steel framed building structure. By default, these connections are semirigid, and accurate analyses of structures including them necessitate quantitative knowledge of their moment-rotation response. A detailed three-dimensional (3D) nonlinear-continuum-based finite element model of the connection region including the composite beam, flush end-plate, blind bolts and the concrete-filled steel tube is developed in this paper. This sophisticated FE model can capture the pertinent physical, geometrical, and contact nonlinearities, and its accuracy is verified against experimental data reported elsewhere in the literature. The calibrated FE model is then employed for a parametric study in which the effects of the slab reinforcement ratio, the thickness of the slab, the degree of the shear connection, the diameter of the blind bolts as well as the pretension force in them and their yield stress, the depth of the beam, and the thickness of the flush end-plate are investigated. The results of the parametric study are employed to calibrate moment-rotation relationships, which are proposed in a convenient analytic form. It is shown that the proposed model predicts the moment-rotation response of blind-bolted flush end-plate composite beam-to-CFST column connections with good accuracy, and it provides a valuable empirical modeling that can be used in the computer design of composite framed building frames in the new paradigm of design by advanced analysis. © 2014 American Society of Civil Engineers.