Bridges, Tunnels and other Transportation Structures
Concrete filled steel tubes (CFST) are composite structural elements which provide an economical alternative to traditional RC columns for their ease of construction and efficient structural properties. In a CFST column, the steel tube acts as the longitudinal and transverse reinforcement to resist flexural, shear, and axial demands, and provides optimal confinement to increase the deformability of the concrete in compression. Recent research has resulted in practical and structurally robust CFST column-to-cap beam and column-to-foundation connections for highway bridge construction in moderate and high seismic regions. One such connection, referred to as the embedded ring (ER) connection, is a fully restrained, full-strength moment resisting connection which relies on an annular ring, welded to the end of the steel tube and embedded in the cap beam or foundation, to anchor the CFST to the concrete cap beam or foundation element. This paper is focused on the development of practical repair strategies for the ER CFST connection following moderate and severe seismic events. The readily identifiable damage state of the ER connection along with the accessibility to the steel tube provides a unique opportunity of repair which is more difficult in RC type connections in which extensive spalling and concrete damage are noted, and longitudinal steel is embedded in the column concrete. Two repair strategies which rely on plastic hinge relocation have been investigated: one which uses fiber reinforced polymers to reinforce the damaged region of the CFST, and one in which the damaged region is encased in concrete, and shear studs are welded to the exterior of the CFST and headed bars are epoxied into the cap beam or foundation to facilitate force transfer. Preliminary results indicate that both repair methodologies are effective shifting inelastic deformation away from the damaged region and restoring the stiffness, strength and deformation capacity of the CFST column.