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Flat Slab Bridge Model for Permit Load Analysis

Flat Slab Bridge Model for Permit Load Analysis synopsis picture

Existing road infrastructure is often exposed to larger number of vehicles and their weight. This process requires bridge engineers to evaluate the existing structures in more detail to meet the requirements of growing transportation needs. State departments of transportation regularly issue load permits for the overloaded trucks, by performing rating calculations of the bridges on the route. ALDOT has an eleven-span flat slab concrete bridge on the northbound side of US Highway 82/231 that was built in 1915 for which there are no construction drawings or other available data. The goals of this research were to define the capacity of the bridge, perform rating calculations, and provide a permit load model. The design methods from early 1900's were reviewed to identify the possible methods used in the original design of this bridge. Field measurements were taken using specialized equipment to assess the dimensions including span length, width, location and size of reinforcement, thickness of the slab, thickness of concrete cover and compressive strength of concrete.  The collected data was analyzed and treated as input data to determine a preliminary load carrying capacity of the slab by AASHTOWare.  An advanced finite element method program ABAQUS was used to develop a 3-D model of the slab.  A sensitivity analysis served as a basis for identifying the most important parameters. The behavior of the bridge slab was then verified by load test, with the load applied using one and two 85-kip 3-axle trucks. The load test results were used to further improve the finite element model and in particular, to develop an improved value for the effective slab width. Proposed newly developed adjustments in the selection of input data in AASHTOWare result in a more rational evaluation and rating of the considered bridge. The full report can be found on our HRC Reports page and was written by G. Garmestani, P.J. Wolert, M.K. Kolodziejczyk, J.M. Stallings and A.S. Nowak.

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