Seismic retrofit of octagonal columns with pedestal and one-way hinge at the base

This study focused on the development of retrofit methods for octagonal single column bents with a pedestal and a one-way hinge detail at the pedestal base. The bents are from a ramp structure built in the late 1960's that is part of a 24-span freeway bridge in Las Vegas, Nevada. Three identical quarter-scale column specimens were built. Two of the columns were tested enhanced with seismic retrofits, the other was tested as-built. The columns were tested in the strong direction, subjected to the 1994 Northridge Sylmar earthquake until failure. The first of the retrofitted columns was tested with a pedestal extension and glass fiber reinforced plastic (GFRP) used as additional pedestal reinforcement. The second retrofitted column was tested with the same retrofit as the first but several of the column bars were severed at the base of the column to reduce plastic shear demand. It was determined that the pedestal retrofit was successful to strengthen the pedestal sufficiently to shift the plastic hinging into the column. The severed column bars lowered shear demand and increased the plastic deformation. Results led to retrofit design recommendations that included the experimentally verified methods.