CFT Column-to-Cap Beam Connections for Accelerated Bridge Construction in Seismic Regions

Due to their increased mechanical properties and ease of construction, Concrete filled steel tubes (CFTs) offer an efficient and economical alternative compared to traditional reinforced concrete columns. Despite their inherent advantages, the implementation of CFT construction within the US is limited due to unverified design expressions and lack of standard connection details. As an effort to facilitate the use of CFTs, a research program has been undertaken by the University of Washington to develop practical connection details for the use of CFTs in bridge construction in seismic regions. The focus of this research is the development of CFT column-to-cap beam connections. Three categories of the CFT column to cap beam connection have been experimentally evaluated; an embedded connection in which the steel tube is embedded in the cap beam concrete, a welded reinforced concrete connection in which headed reinforcing bars are welded to the inside of the steel tube and extended into the cap beam, and a reinforced concrete connection in which a traditional reinforced concrete cage is placed within the CFT column and extended into the cap beam. Experimental results show that these connections can achieve strength and ductility objectives with limited damage to superstructure components.