Effect of Girder Damage on the Structural Behavior of Slab-on-Girder Bridges

A Master of Science thesis in Civil Engineering submitted by Ahmed E. Elozn entitled, "Effect of Girder Damage on the Structural Behavior of Slab-on-Girder Bridges," submitted in June 2011. Available are both soft and hard copies of the thesis.

Abstract

There are many bridges around the world that have been constructed with inadequate vertical clearance. Such bridges are susceptible to over-height vehicle collisions, causing damage to the underside of the supporting girders. The incurred damage leads to redistribution of load among the girders. The objective of this study is to investigate the effect of minor damage in the exterior girder on the behavior of composite steel girder bridges subjected to live load. This is done through numerical studies involving finite element modeling of various bridges with different geometry. Linearly elastic material behavior is utilized since the loading condition is that of a serviceability criterion, and the damaged girder is eventually repaired after a short period of time following the next inspection. Different extent of damage in the exterior girder is considered, and their effect on the live load distribution factor for shear and moment in the exterior and adjacent interior girders is studied. The damage in the girders is confined to the lower part of the web and bottom flange, at different distortion angles. The study showed that the reduced stiffness of the damaged exterior girder pushes live load away from it to the nearby undamaged interior girders; thus, the girder distribution factor in the exterior girder reduces and the same for the adjacent interior girder(s) increases. Also, damage to the exterior girder significantly impact the flexural live load redistribution in a steel girder bridge but does not have a measurable effect on the shear live load redistribution. For the flexural live load effect, the percentage decrease in the exterior girder's distribution factor reaches about 50-70% when the damage distorts the exterior steel girder web by 45o. The corresponding increases in the girder distribution factor for the first and second interior girders are within the ranges 40-50% and 5-15%, respectively. For the 45o damage distortion angle, the live load flexural effect to flexural capacity ratio of the damaged exterior girder increases many times over the same ratio in an undamaged exterior girder.