Influence of shear key performance on the fatigue life of adjacent beam bridges

Adjacent beam bridges, such as box beams and hollow core bridges have been one of the most popular forms of precast prestressed bridges in the past. Recently, an awareness of major durability problems has led owners to make improvements to the old standards or move away from the system completely. These issues usually stem from the breakdown of the shear key which provides continuity between adjacent members. This research focuses on determining the best improvements that will reduce durability issues and increase the bridge's service life.A review of previous research performed on adjacent beam bridges is performed, focusing on shear key design and post-tensioning requirements. State Departments of Transportation were also surveyed on their past use of this bridge type and the observed performance of their standard details. Conclusions were gathered concerning the changes in shear key design, post-tensioning and overlay requirements to determine what design methods had the most impact on bridge performance.A fatigue study modeling the standard hollow core bridge sections used in South Carolina was performed using Monte Carlo simulations with Latin Hypercube sampling. This study was used to determine the influence of average annual daily traffic (AADT), corrosive environment and shear key degradation on the service life of an adjacent beam bridge. Most physical and material properties of the simulated bridge were treated as random variables. The program only considered heavy truck loads as damage inducers.The fatigue study found that shear key performance, AADT and the corrosive environment of the bridge all have significant effect on the service life of a structure. It was found that if a shear key performed well enough to perfectly emulate a cast-in-place slab, the hollow core detail could be considered for use on roads with up to 50,000 AADT.