Seismic performance of precast segmental bridge columns with resettable sliding joints: friction at interface

Abstract

In an attempt to promote the use of precast segmental bridge columns in regions of moderate to high seismicity, sliding planar joints have been adopted to relieve the adverse effects of seismic action. However, despite the ability to survive, the sliding segments often result in noticeable residual relative movements after an earthquake, which require costly repairs. With the increasing occurrence of super typhoons, the ability of bridges to resist extreme wind loads is also a concern. It is desirable to improve and provide the system of sliding segments the self-centering capability and sufficient lateral resistance without unduly high prestressing forces. Similar to the isolation mechanism provided in most of the mechanical sliding bearings, lateral relative sliding displacement is permitted at the sliding joints by dry contact between adjacent segments. To ensure sufficient capability of seismic isolation and to avoid excessive magnitudes of co-existing rocking displacements, it is desirable to keep the coefficient of friction at the segment-to-segment interfaces reasonably low. The challenge is to control the coefficient of friction at the interfaces within a suitable range. The resetting guide keys can be so designed to provide sufficient resistance to wind and other actions. This paper reports some initial experimental investigations on possible ways to achieve a reasonably low coefficient of friction, including (a) lubrication using powder, (b) lubrication using grease, (c) chemical polishing treatment, and (d) combinations of the above. By varying the coefficient of friction within the practical range, the seismic performance of precast segmental bridge columns with resettable sliding joints is studied numerically to identify possible directions for further improvement.