Experimental and Numerical Investigation of the Tensile Behavior of Blind-Bolted T-Stub Connections to Concrete-Filled Circular Columns

This paper presents the results of two series of experimental and analytical studies on the structural behavior of an innovative moment-resisting connection to concrete-filled circular hollow sections using blind bolts. The first part of the paper presents a large-scale T-stub connection with full instrumentation tested to failure in tension, and the second part presents a series of pullout tests to explore the anchorage behavior of cogged bars within concrete-filled steel tubes. The favorable strength and stiffness characteristics of this type of connection showed that it could be an alternative to conventional welded moment-resisting connections. A 3D finite-element (FE) model was developed to simulate the behavior of blind-bolted T-stub connections when subject to tension. The FE model took into account material nonlinearities, geometrical discontinuities, and complex contact interactions among the bolt heads, tube wall, end plates, and nuts. The FE results were found to be in good quantitative agreement with the actual connection behavior. A stiffness model composed of various nonlinear springs was also developed to predict the pullout behavior of cogged bars within concrete-filled steel tubes. The cogged extensions to the blind bolts were very effective in relieving the stress concentration on the thin tube wall. The tensile load can be shared between membrane action of the tube wall and anchorage of the cogged bars. Thus, by using the blind-bolted connections with cogged extensions to connect the beam flanges to the column, moment transfer between the beam and column can be effectively achieved within a structural frame of composite construction.