Self-Stressing Composite Steel Bridge Girder System

Flexural continuity over the interior supports of steel girder bridges reduces the forces within the spans while creating negative moments at the supports. The negative moment creates tension at the top of the structure and can lead to a cracking of the deck near the piers, which then allows moisture and deicing chemicals to penetrate the slab, resulting in its degradation. One remedy is to create a state of precompression in the slab to reduce the size and extent of the cracking. The self-stressing system achieves this state of compression in a two-span bridge by constructing the bridge deck with the interior support raised. Once the slab has been cast and cured, the center support is lowered in the final position. Continuity of the steel member results in the development of compressive stresses within the slab in response to the lowering of the support. This initial compressive force counters the tensile stresses resulting from live load and prevents crack formation along with the associated deleterious effects. Experimental investigations were performed on both cast-in-place and precast specimens observing the time-dependent behavior and performance under ultimate loading. The results indicated that the system performed as expected and increased the level of load at which cracking of the deck occurred.