Influence of time dependent properties and temperature effects on the performance of composite bridge girders

Abstract

This dissertation seeks to understand the mechanical properties of concrete, and its interaction with steel bridge girders with the purposes of deepening our understanding of the behavior of steel girder bridges made composite with concrete slabs. This research program identifies and documents several causes for undesirable elevation profiles and recommends design and construction practices to help mitigate problems associated with unwanted deformations and extend the life span of bridges. Forensic investigations were performed on field bridges provided evidence that poor elevation control and improper construction practices resulted in unevenness in bridge deck elevations and thin bridge decks. Additionally, laboratory testing on overhang brackets confirmed that the commercially available brackets used for bridge rehabilitation are insufficient to support the deck cantilevers outside the exterior girders. Accordingly, these brackets are unable to provide the elevations control resulting in poor elevation controls and thin bridge decks.

A full-scale prototype bridge was built and instrumented at the Bert Cooper Engineering Laboratory at Oklahoma State University in Stillwater, OK USA. The concrete strains associated with volume change, including both temperature-related strains and shrinkage strains, were found large enough to be considered as one possible cause for adverse ride quality and unwanted deformations in steel girder bridge. Real-time thermal loading was applied to the bridge deck of the laboratory prototype bridge. The temperature gradients developed in the bridge deck produced internal thermal strains and stresses that directly resulted in bridge deformations. A large array of electronic gauges and sensors were employed to measure and monitor concrete and steel strains, concrete and steel temperatures, overall bridge deflections and inclinations. Synthesis of data collected from the sensors along with analytical computational models that were developed using the measured constitutive properties of concrete validated the methods for structural monitoring. This dissertation provides a practical means of monitoring bridge performance and offers a good experience for implementation and structural monitoring for both laboratory and field bridges. The dissertation demonstrates that the cumulative effect due to volumetric changes in concrete, temperature effects and poor bracing system can adversely affect the ride quality, cause deck cracking and excessive deflections, decrease durability and reduce long-term performance of steel girder bridges.