Experimental behavior of connections to concrete-filled steel tubes

Six large-scale connections were tested to failure using the quasi-static test method. All details consisted of a connection-stub which was shop fabricated and field bolted for construction. Experimental results indicated that welding the connection-stub directly to the skin of the steel tube resulted in a large deformation demand on the tube wall. Large tube wall distortions made the girder flange, the flange weld, and the tube wall highly, susceptible to fracture. Inelastic cyclic behavior improved when external diaphragms were used to distribute the flange forces around the tribe, and the connection was able to develop the bending strength of the girder. Using embedded elements to distribute the girder flange force to the concrete core was very efficient in alleviating the stress concentration on the tube wall, however; the connection performance was sensitive to the type of embedded elements. Deformed bars welded to the girder flange and embedded into the concrete core developed a connection strength of more than 1.5 times the plastic bending strength of the connected girder, and exhibited stable hysteretic behavior up to failure. Connections with continuous flange plates showed less promise without additional derailing to anchor the flange plate into the concrete core. Extending the girder connection-stub through the entire CFT column was sufficient to develop the full plastic bending strength of the connected girder, and exhibited favorable inelastic cyclic performance. (C) 1998 Elsevier Science Ltd. All rights reserved.