Hybrid bridge bent using stretch length anchors with post-tensioning and shear key alternatives

Abstract

Precast concrete bridge bents are good candidates for accelerating bridge construction. In seismic regions, in addition to construction speed, there is a need to improve seismic performance of bridges. One promising solution is self-centering bridge bents that use post-tensioning and external energy-dissipation devices as a hybrid system. This paper presents cyclic load experiments of hybrid two-column bridge bents to assess their performance regarding self-centering and hysteretic energy dissipation. The cyclic experiments were conducted on 42% scaled bridge bents that used unbonded post-tensioning (PT) bars for self-centering and stretch length anchors (SLAs) as external energy dissipators. A total of six experiments are investigated: three with PT bars and SLAs and three with PT bars only. The variables included the number of PT bars in each column (two or four), the initial post-tensioning force in the columns, and the shear key details in the footings and cap beam. The PT bars remained elastic until 4.0% drift ratio but some variation was observed in the post-tensioning forces especially for columns with two PT bars. For post-tensioned bridge bents with or without SLAs, increasing the number of PT bars in each column from two to four enabled efficient self-centering by limiting the residual drift ratio to 0.5%. There was no damage to the concrete for bents with four PT bars and there was repairable concrete damage for bents with two PT bars. The hysteretic energy dissipated by bridge bents with SLAs in addition to PT bars was 1.8 to 3.2 times the hysteretic energy of bridge bents with only PT bars.