Assessment of Cross-Tie Performance in Bridge Pier Walls

摘要

Following the 1989 Loma Prieta earthquake, the California Department ofTransportation intensified its efforts to verify and, if necessary, upgrade the seismic design of the structural components of highway bridges. The very early design procedures of pier walls assumed that these structural components behave as shear walls subjected to equivalent static loading. Lateral loads in the direction of the weak axis (flexural) of such walls were not considered in the design. As a result of this assumption, the pre-1971 pier wall design used relatively small reinforcement ratios in both the vertical and horizontal directions. The present study intended, specifically, to examine a range of cross-tie provisions with the objective of establishing whether existing standards are unnecessarily conservative and, if so, what level of confinement would be acceptable. In addition, two different ratios of the vertical steel reinforcement representing average and upper design limits in current Caltrans specifications were investigated. A computer program was developed to estimate both the pier wall ductility and strength. Furthermore, the current design method used by Caltrans designers was assessed. The calculated results were compared with the experimental findings, and recommendations for improved design procedures were devised.