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Title: Condition Assessment and Load Rating for a Cracked Widened Bridge

Author(s): Nestor R. Rubiano

Publication: Web Session

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DOI:

Date: 11/19/2018

Abstract:
A 15-span concrete bridge was built in 1965 over the Little Tallahatchie River in Union County, MS along the US 78 Highway by the Mississippi Department of Transportation (MDOT). Twelve of the spans used prestressed precast concrete beams while the three spans over the river used a continuous cast-in-place concrete multi-box beam unit. The bridge was built with a total deck width of 63 ft to accommodate two lanes of traffic in each direction. In 2013, the bridge was widened to increase the total roadway width to 108 ft and provide three traffic lanes in each direction. This widening was done using precast prestressed girders simply supported for dead loads and continuous for live loads. Less than two years after the widening was completed, cracks appeared at several locations along the longitudinal construction joint between the original deck and the widened deck within the spans of the continuous multi-box beam. Repairs were carried out by MDOT, but cracks re-appeared shortly thereafter and subsequent local deck deterioration due to traffic was evident. A detailed inspection of the superstructure and substructure was conducted to investigate the extent of deterioration and assess the overall condition of the bridge. Cracks were found not only on the concrete deck but also in some of the box beam webs. Substructure was in good condition with no signs of distress. A Finite Element model of the damaged 3-Span Continuous unit was developed to evaluate the stresses in the superstructure elements. The model included two stages of construction: first the continuous cast-in-place concrete multi-box beam and then, the widening prestressed precast beams with the composite concrete deck slab. Analysis of the bridge model revealed stress concentrations along the interface caused by the different stiffness of the original bridge and the widening. These results confirmed the cause behind the deck cracking. The Finite Element model was also used to determine the load rating of the bridge. Based on the analysis results and the load rating, a set of recommendations were formulated to MDOT for the rehabilitation of the bridge.