The transition between bridge approach slabs and the bridge deck itself often settle at different rates, causing a “bump” for motor vehicles and maintenance problems associated with approach slab deterioration.
CFIRE affiliate researchers recently completed a CFIRE-funded project that aimed to improve the performance of highway bridge approach slabs by quantifying the amount of rotation that could develop between an approach slab after base settlement and a bridge abutment. CFIRE associate director Michael Oliva led the project.
The research team quantified the problems — particularly cracking and rotations — associated with approach slabs by analyzing a number of parameters including approach slab length, slab material, subgrade soil type, abutment height, and possible trenches that may develop under the slab near its support on the abutment.
As a result of these analyses, researchers reached conclusions about both approach slab end rotation and approach slab cracking. The end rotation of the approach slab near the abutment varied depending on geometry of the approach slab, trench and abutment as well as with the stiffness of the soil and concrete used in the analyses. The susceptibility of the approach slab to cracking was influenced by the height of the abutment, trench length, slab length, soil stiffness, and concrete stiffness. Taller abutments increase the likelihood of concrete cracking in the approach slab. The length of the approach slab has little effect on the likelihood of cracking or amount of end rotation for slabs greater than ten feet in length. Stiff soil under the approach slab reduced the probability of concrete cracking. The risk of concrete cracking increased as the soil stiffness decreased.
This information might be used to create a better approach-bridge transition using ductile concrete to directly connect the approach slab to the bridge deck.
For more information about this project and to read the final report, visit the CFIRE 03-10 project page.