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Shrinkage and Temperature Induced Deformations in Steel Bridges Made Composite with Concrete Deck Slabs
Civil & Environmental Engineering
Concrete Bridge decks are typically cast upon steel or precast concrete girders. The new concrete, upon taking its initial set begins to change in volume. This volume change in concrete is caused by temperature changes, creep of concrete or drying shrinkage. These time dependent volume changes affect the ride quality, deck cracking, deflection, serviceability, durability and long-term performance of steel girder bridges. Theoretically, compressive strains caused due to the time-dependent volume change result in excessive and unpredicted deflections in bridge girders. Moreover concrete bridge decks are subjected to repeated temperature fluctuations that, in turn, cause temperature gradients throughout the depth of the slab. Typically, concrete decks are heated by direct summer sunshine and by high mid-day temperatures. The temperature gradients within the deck and cross-section cause internal thermal stresses that directly cause overall upward deflections.
This research is currently undertaken at the Bert Cooper Engineering Lab at Oklahoma State University, one of the largest structural engineering laboratories in the country. The principal client and sponsor for this research program is the Oklahoma Department of Transportation (ODOT). A full scale 40 ft simple span bridge that mimics the existing State Highway 14 Bridge is being built in the lab. A total of 77 sensors will be installed on the bridge to measure shrinkage strains and concrete temperature, bridge deflections and rotations at the support. The surface of bridge deck will be heated to replicate the summer temperatures in Oklahoma. Analytical models were developed to replicate the AASHTO temperature gradient and will be tested against the experimental data. Prior to concrete pour, load tests will be performed on the bracings to monitor the stiffness and deflections due to deck and walkway loadings. The test data will enable to identify the most likely causes for excessive or unpredicted bridge deflections. Based on the test results recommendations will be made to develop and refine design and construction methods for ODOT bridges.