Seismic performance of high strength vanadium alloy concrete filled tube column-footing connections

High-strength steel structural members can offer significant economic advantages compared to normal strength steel by reducing the material required for a given quantity of resistance. However, reduced sections can be susceptible to local instability resulting in premature failure. In concrete filled tube (CFT) columns, these concerns are minimized in that the concrete fill restrains buckling of the tube permitting full tensile strength of the steel to be utilized. Despite the improved structural performance that concrete-filled tubes may offer over steel or reinforced concrete alone, use of concrete-filled tubes as flexural members is limited in the United States, because reliable and constructible connection designs are still in the early stages of development. An ongoing research study at the University of Washington was initiated to develop reliable connections for circular CFT columns constructed using for high-strength, vanadium micro-alloyed steel. The research examines a wide range of applications for seismic and non-seismic design, and it addresses methods for rapid and economical fabrication and construction. Experimental methods were used to evaluate the performance of CFT made from spiral welded, vanadium-alloy high-strength steel tubes (termed CFVST construction) and column-based connections. The influence of the primary connection parameters including embedment depth, high performance concrete, footing reinforcement, and construction procedure were consideration. The experimental results indicate that the connection contributes significantly to the global response. These research results are summarized, and used to evaluate current and develop improved recommendations for CFT column and connections.