Effectiveness and Implications of Seismic Retrofit Measures for Deck Unseating of Multiframe Bridges with Regular and Irregular Geometry

Abstract

Deck unseating at abutments and in-span hinges can be a major cause of collapse, especially for older multiframe bridges that are not in compliance with the latest code provisions for seat lengths. This study investigated the effectiveness and implications of using two common retrofit measures to reduce or eliminate deck unseating risks: restrainer cables, and shear keys. A combination of restrainer cables and shear keys at the abutments and the in-span hinge was proposed and investigated as a potential retrofit measure to limit excessive movement of decks and eliminate unseating risks of older multiframe RC bridges with regular and irregular geometry. Six four-span multiframe bridge configurations were considered: straight, skewed, and curved bridges, with equal and unequal pier heights. Detailed finite-element models for all configurations were developed to conduct nonlinear time history analysis (NTHA) under five different ground motions representing weak, moderate, and strong earthquake scenarios. The average of the NTHA results showed that the combination of restrainer cables and shear keys is more effective than using individual measures to reduce displacement demands for irregular bridge configurations, in which coupling between the response in the longitudinal and transverse directions is more pronounced.