Development of Improved Connection Details for Adjacent Prestressed Member Bridges

About the report:

Adjacent prestressed member girder bridges are economical systems for short spans and generally come in two types: adjacent box beam bridges and adjacent voided slab bridges. Each type provides the advantages of having low clearances because of their shallow section depths, accelerated construction times, and high torsional stiffness. The current longitudinal connection detail, a partial depth grouted shear key, has been known to fail in many of these bridges. The failure leads to reflective cracking in the wearing surface, which allows chloride-laden water to seep through the joint, where it can corrode the reinforcement and prestressing strand. Ultimately, the failed keys lead to costly repairs and bridge replacements sooner than their proposed lifespan. Failed keys also lead to poor load sharing, which in turn could result in beams carrying more load than that for which they were designed.

This study was composed of three distinct phases: testing of in-service adjacent member bridges; finite element modeling of these bridges; and testing of adjacent box beam and voided slab sub-assemblages. The sub-assemblages were designed to replicate behavior in a full-sized adjacent member bridge and were constructed with five alternate connections (in each girder type) as well as a control specimen with the current joint detail. The objective was to compare the tested details and to find a connection that abated cracking in the shear key. The tested connections employed alternate connection shapes and two different mix designs of fiber-reinforced, high-strength concrete.

The results showed that all alternative connections outperformed the current detail. The best performing connection included blocked out concrete at adjacent stirrups. A short reinforcing bar was placed in the blockout to lap the stirrups on adjacent beams. The blockout was filled with a fiber-reinforced, high-strength concrete. This connection survived 1 million load cycles mimicking an HL-93 truck with little or no cracking and no leakage.

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