Research Projects

Studies on the ductile detailing of steel connections gathered momentum since the 1994 Northridge earthquake, where, welded steel joints underwent brittle failure. The unprecedented collapse of steel structures from the 1995 Kobe earthquake and the 2011 Tohoku earthquake have shattered the illusion that steel is a ductile material and steel structures will undergo ductile failure. It has become a protocol to avoid site welding at all cost due to its brittle failure, and to provide stiffening plates at moment resisting beam-column connections to develop adequate rotational capacity. However, it is tedious to follow this protocol in a beam-column connection made of tubular steel members. Seismic experts tend to discourage the use of tubular steel members in seismic resistant framing system. Even though tubular steel is an efficient cross-section due to its high-strength-to-weight ratio and high torsional rigidity, it is not utilized in seismic resistant lateral framing systems. The advancement in the research of concrete-filled steel tubular (CFST) cross-sections has encouraged developers to choose CFST columns in tall buildings, bridge piers and commercial complexes. It has high-strength and high-stiffness properties due to the synergistic action between concrete and steel. The major constraint in implementing and utilizing the superior structural performance of tubular steel lies in developing a ductile moment resisting connection. In the current construction practice, tubular steel connections are heavily dependent on-site welding or blind-bolting that are quite expensive. Therefore, in this project, a new bolted connection method is proposed for a steel-concrete composite tubular beam-column connection. Concrete filled double steel tube (CFDST), a variant of CFST is selected as a column cross-section. Here, the steel I-beam is directly connected to the inner steel tube of CFDST using conventional bolts and they are secured with nuts which is held on to the inner steel tube surface. A preliminary numerical study conducted on the proposed beam-column connection reveal that the proposed connections have higher strength and rotational capacities, which indicate improved ductility, conforming to Eurocode specifications. It has to be confirmed through experiments. In this project, monotonic and cyclic tests will be carried out on the proposed beam-column connection. The key findings from the tests will be an important input in drafting the design standards for the ductile detailing of tubular steel and tubular steel-concrete composite connections in general. The project includes a comprehensive literature review, connection test under monotonic and cyclic loading supported with numerical simulations for further parametric studies. Finally, design guidelines with worked out examples will be developed for the effective utilization of the proposed connection.