Rocking Bridge Columns with External Replaceable Tendons

Abstract

Columns are usually the weak links in conventional bridges with regard to seismic design. Damage of reinforced concrete (RC) columns caused by moderate earthquakes is usually repairable, but significant damage is expected in the event of strong ground shaking. Advanced materials and/or innovative detailing have been developed for RC bridge columns to minimize damage while meeting or exceeding the ductility requirements per current codes. Rocking columns with either internal or external energy dissipators, commonly referred to as hybrid rocking columns, are novel columns with an improved seismic performance. Despite decades of research on rocking columns and promising laboratory findings, they have never been used in any bridge in the United States because of concerns regarding the accessibility and durability of internal tendons, and the lack of system redundancy when tendons are lost. The present study proposes a new class of rocking bridge columns that do not need internal pre- or post-tensioning tendons (or bars). Instead, tendons are placed outside of the column to be fully accessible and replaceable. One half-scale precast bridge column cast with ultrahigh performance concrete (UHPC) was tested twice under the same loading protocol. All external tendons were replaced in the second round of testing to validate repair by the fuse replacement technique. The damage of the precast UHPC column was insignificant throughout testing and retesting. Furthermore, the precast column showed the same displacement capacity, a slightly lower lateral strength, and insignificant residual displacements compared with those of a reference cast-in-place column (CIP). One drawback of the precast column was a lower effective stiffness compared with that of CIP column. A parametric pushover study was performed to investigate the seismic performance of the proposed columns with different fuse materials and lengths and to determine the best fuse configurations for a successful design. Finally, design guidelines were recommended to facilitate future investigations.