United States Department of Transportation
i
Combining Link Slab, Deck Sliding over Backwall, and Revising Bearings
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2008-08-31
[PDF-2.60 MB]
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TRIS Online Accession Number:1115075
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Abstract:The new bridge design trend is to avoid having expansion joints over piers and abutments to prevent premature deterioration of bridges due to faulty joints. For this purpose joints over the piers are eliminated using link slabs where the deck is continuous and the underlying girders are simply supported. The expansion joints over the abutments are also eliminated by allowing the deck to slide over the backwall or by allowing the deck-backwall combined system to slide over the abutment (semi-integral abutments). Consequently, the movement of the superstructure is transferred to the ends of the approach slab that sits on a sleeper slab. The research was designed to respond to the concerns of the designers in terms of the design of specific components and field performance of a limited number of bridges retrofitted with the link slab deck system. Three tasks were performed in this project. The first task was to review and synthesize information related to the behavior, performance, design, and analysis of jointless bridges with link slabs. The second task was to document the distress at the sleeper slab and bearings in Michigan jointless bridges associated with the link slab, approach slab, abutments, pier caps, and expansion joints. The third and final task was to develop analysis models of the jointless bridge deck system including link slab, bearings, abutment types (deck sliding over backwall and backwall sliding over abutment), approach slab, and sleeper slab. Based on literature reviewed, field inspection data analysis, finite element modeling, and subsequent simulations of the numerous models developed in this project, four design recommendations are developed. One recommendation deals with the link slab design and the remaining three deal with the backwall and approach slab region. Current link slab design is solely based on the moment demand due to live load, but AASHTO LRFD (2004) Service I limit state requires a combined effect of live and thermal load in calculating link slab moment demand. Hence, a new analysis procedure is proposed for calculating link slab design moment and axial load from thermal gradient load.
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