Damage Identification in Prestressed Concrete Continuous Girder Bridges Using Spatial Patterns of Deflection Influence Line Changes

Changes in deflection influence lines may help identify damage in prestressed continuous girder bridges. This study investigates three conditions in a prestressed concrete bridge: bearing disengagement, local flexural damage, and global prestress loss. A three-dimensional finite element model of a three-span bridge was first compared with a measured strain influence line in the healthy state. Deflection influence line changes were then calculated at nine measurement points for each damage case under the same test load. The three conditions produced different patterns. Bearing disengagement mainly affected the two spans beside the bearing. Flexural damage in the middle span produced the largest changes when that span was loaded. Under global prestress loss, all three spans contributed substantially, and each midspan point changed most when its own span was loaded. To measure these patterns, the absolute influence line changes over each loaded span were investigated, adjusted for span length, and combined the results from three midspan points. Two ratios comparing the smaller span contributions with the largest one separated the simulated cases into one-span, twospan, and three-span response patterns using a 50% threshold. The same patterns were found in nine corresponding cases on a second bridge with unequal spans. The participating spans pointed to the affected span or support in the local damage cases. These results suggest that spatial patterns of influence line changes can help guide targeted inspection of continuous girder bridges.