Following the 1989 Loma Prieta earthquake, the California Department of Transportation intensified its efforts to verify and, if necessary, upgrade the seismic design of the structural components of highway bridges. This paper summarizes the findings of three different experimental studies conducted at the University of California, Irvine. The first investigation made an experimental and theoretical assessment of the seismic behavior of existing pier walls and established a basis for the retrofit of these walls to improve their seismic resistance. Good correlation was found between the calculated ductility and strength and those observed experimentally of twelve half-scale specimens. It was found that the lap length splice of the vertical steel reinforcement had a significant effect on the ductility of the walls. The observed displacement ductility factor was higher than the design ductility factor. An optimal retrofit scheme was also devised and tested. The second testing program evaluated the strength and ductility of modern bridge pier walls built to present seismic design standards. The study specifically examined a range of cross tie provisions with the objective of establishing whether existing standards are unnecessarily severe and, if so, what level of confinement would be acceptable. Six half-scale specimens with three different distributions of the cross ties and two different vertical reinforcement ratios were tested. Finally, a study was conducted to investigate the behavior of bridge pinned columns to assess the effectiveness of depressed shear keys on the total shear resistance of the column pins and to determine the relationship between their shear capacity and the imposed rotational ductility of the column. Six reduced-scale columns with two different pin details were cycled laterally and then tested to determine the ultimate shear strength. Modified code formulae are proposed to pinpoint the failure load and failure mechanism of the tested columns.
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