Experimental study on concrete filled steel tubes to footing connection using ultra-high performance concrete

Abstract

Concrete filled steel tubes (CFSTs) provide improved structural strength and ductility in addition to eliminating the need for column formwork. This research proposes new connection details for column-to-footing connection using ultra-high performance concrete (UHPC). Two connections consisting of an embedded and an encased layer of UHPC were selected for the experimental program. In these details, the CFST is embedded in a layer of UHPC located near the plastic hinge zone of the column and steel dowels from the footings are used for force transfer. The sequence of construction and detailing allows the use of these connection details for accelerated bridge construction (ABC) applications. Two columns were tested under a combination of constant axial and incremental cyclic lateral load. The embedded type connection failed by fracture of the tube while the encased type connection induced damages in the UHPC encasement. Both connections exhibited high levels of ductility and did not show significant loss of lateral load capacity. The load hysteresis of the embedded connection showed higher energy dissipation for the embedded connection when compared to the encased connection due to damages in the UHPC encasement. The capacity protected footing did not show any signs of cracking.