Failure investigation and retrofitting of a long-span rail-cum-road bridge through field response measurements

Abstract

Many of the existing age-old bridges connecting railways and highway networks need to be assessed for their structural integrity, degradation due to ambient load effects and environmental conditions and adequacy to the increased load demands. Field testing and evaluating the structural performance of bridges is becoming essential as most of the bridges that are serving are becoming old and deteriorating because of environmental effects, increase in vehicular loading, poor maintenance etc. In the present paper, detailed investigations carried out on an age-old in-service openweb girder type long-span rail-cum-road bridge through extensive instrumentation and field testing are discussed in order to assess the failure of the members , excessive vibration and to formulate appropriate retrofitting procedure. As the bridge experiences distress and damage on some of the members, it became necessary to investigate and assess the structural performance of the bridge through ensor based response measurements assisted with analytical studies.Instrumentation and field testing of the bridge has been carried out to measure the structural and vibration responses of damaged and undamaged portals of one of the bridge span under moving vehicular and train loading. Numerical modeling at both global and local level is carried out to simulate the responses obtained from the field testing. It is found that, the cross girders of the portal at intermediate expansion joint locations are subjected to excessive torsion due to improper seating of the stringer beams at the edge of the cross girder flange. By assessing the requirement and envisaging the practical suitability, a suitable retrofitting scheme is designed.