Model for Permit Loads for Barnes Slough Bridge

Abstract

ALDOT has an eleven-span flat slab concrete bridge over Barnes Slough and Jenkins Creek 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. This bridge is referred to as “Barnes Slough Bridge”. The goals of this research are to define the capacity of Barnes Slough Bridge, rate the bridge, and provide a permit model that can be modeled in AASHTOWare software. ALDOT can then use this model to provide permits for non-standard trucks to travel over this bridge. These goals were achieved in four steps. First, the design methods from early 1900s were reviewed with an aim to identify the methods used to design this bridge. Second, field measurements and tests were performed to confirm the accuracy of assumptions made based on the literature review. Third, the data collected from field measurements were analyzed to finalize the characteristics and parameters that would be used to define the capacity of the Barnes Slough Bridge. Fourth, this information was used to build a permit model of the Barnes Slough Bridge in AASHTOWare. The permit model is a model of one effective width of slab. This research defined the cross sectional capacity of the Barnes Slough Bridge and provided load ratings. However, the performance of the structure through its life and during the live load tests suggests that the structure has significant capacity and perhaps more than the expected capacity shown in analyses. Hence, choosing an effective width larger than the value defined by AASHTO was the most appropriate parameter that could incorporate additional capacity into an AASHTOWare model while keeping the measured parameters the same as those measured. These findings suggest that the load ratings and the permit model given in this research underestimates the true capacity of this bridge. Future work by others will provide finite element based ratings of this structure to define the actual effective width. Upon completion of that work ALDOT will then be able to choose a final effective width for the permit model.