First application of second-generation steel-free deck slabs for bridge rehabilitation

摘要

The arching action in concrete deck slabs for girder bridges is utilized fully in steel-free deck slabs. These concrete slabs, requiring no tensile reinforcement, are confined longitudinally by making them composite with the girders, and transversely by external steel straps connecting the top flanges of external girders. Between 1995 and 1999. five steel-free deck slabs without any tensile reinforcement were cast on Canadian bridges. All these slabs developed fairly wide full-depth cracks roughly midway between the girders. While extensive fatigue testing done in the past three years has confirmed that the presence of even wide cracks does not pose any danger to the safety of the structures, wide cracks are generally not acceptable to bridge engineers. The developers of the steel-free deck slabs have now conceded that these slabs should be reinforced with a crack-control mesh of nominal glass fibre reinforced polymer (GFRP) bars. Steel-free deck slabs with crack-control meshes are being referred as the second generation slabs. With the help of testing on full-scale models, it has been found that deck slabs with GFRP bars have the best fatigue resistance and those with steel bars the worst. The second generation steel-free deck slab is economical and highly durable in corrosive environments created by deicing salts. The first application of the second-generation slab was on one span of the ten-span Red River Bridge on the North Perimeter Highway in Winnipeg, Canada. The existing concrete deck of this bridge was replaced during the summer of 2003. The purpose of this paper is to introduce the second-generation steel-free deck slab in general, and to discuss the specific design details of the project. In addition to comparing the cost of the second generation steel-free deck with that of conventional reinforced concrete deck slabs, the paper will also report on the structural health monitoring of the deck slab and external steel straps. It will be shown that the use of external straps leads to the highest static strength of the deck slab, and the GFRP crack-control grid provides an economical solution to the problem of wide cracks.