Self-Centering Bridge Bent with Stretch Length Anchors as a Tension-Only Hysteretic Hybrid System

Abstract

Accelerated bridge construction (ABC) incorporates innovative techniques to reduce construction time and traffic disruption. The objective of the research was to design, build, and test a seismically resilient bridge bent using ABC methods, which can self-center, thus remaining functional after a large earthquake with minimal repairs. The design criteria were to achieve a drift ratio of 2.0% without concrete damage, mild steel reinforcement yielding, or post-tensioned (PT) bars yielding. A tension-only hybrid system was designed and tested with similar characteristics to conventional hybrid systems. The distinguishing feature of the system is that the hysteretic component consists of stretch length anchors (SLA) designed to elongate and dissipate hysteretic energy only in tension. SLAs are intentionally built, so they do not experience compression forces, do not need to be protected against buckling, and have a long fatigue life; moreover, they do not impede recentering because hysteretic energy dissipation occurs only under tensile stress. SLAs are readily available; they are affordable and are easy to replace after an earthquake. A two-column precast concrete bridge bent was tested under quasi-static cyclic loads. Unbonded post-tensioned (PT) bars were used to connect the reinforced concrete cap-beam, columns, and footings for recentering the structural system. Column mild steel reinforcement did not cross the column-to-footing or column-to-cap-beam interfaces. SLAs were attached at the top and bottom of the column externally and were constructed so they could be replaced easily after an earthquake. SLAs yielded and elongated in tension at a 1.2% drift ratio; the PT bars and gravity load were effective in self-centering the structural system. The specimen met the design criteria, with a maximum residual drift ratio of 1.1% at a maximum imposed 6.0% drift ratio, while the structural system experienced repairable damage.