Effect of confinement from lateral restraints in steel-free circular deck models under static loading

The concept of a steel-free bridge deck is based on the compressive arching action of the concrete deck when it is subjected to concentrated loads. It is well established now and has successfully demonstrated that the removal of entire internal reinforcement from the bridge deck slab is possible provided that the slab is suitably confined in both the longitudinal and transverse directions. In the longitudinal direction, the deck slab is confined by making it composite with the beams and by edge beams. In the transverse direction, the confinement is provided by steel straps on the top flanges of the girders. These steel straps resist tensile stresses and provide the lateral restraining force to the deck slab thereby enabling the slab to sustain loads through arching action. The internal arching action, hence the lateral restraint, is a key parameter to the performance of the steel-free bridge deck. As well, an equally important fact in determining the punching failure criteria in concrete is that the concrete zone surrounding the point of load of application is in a state of three dimensional stress. As a result of this, the principle compressive stress around the load point can reach values well in excess of the uniaxial compressive stress f'c. Accordingly, this three dimensional stress state is both a key to sustaining high loads and a limiting factor in determining the failure criteria.; The scope of this research project was to experimentally investigate the ultimate load characteristics and the failure mechanism of the steel-free deck system for different degrees of lateral restraints and to compare the results with the PUNCH program. The PUNCH program was developed for predicting the punching behavior of steel-free bridge decks. A rational mechanics model of a circular slab defined by the largest circle of the diameter, which is inscribed between the adjacent girders, was assumed for this PUNCH program. A physical model similar to the mechanics model was selected for this study. The specimens were made from steel-free concrete. To control plastic shrinkage cracks, polypropylene fibers (randomly distributed low modulus of fibers) were mixed with the concrete. Altogether 9 specimens were constructed and confinement was provided in different ways; using a ring beam; using external radial steel straps; and using external Carbon Fibre Reinforcement Polymer (CFRP) wraps in circumferential direction. Specimens were also tested without any confinement for the purpose of comparison. All the specimens were tested under static loading until failure and the crack patterns, ultimate failure loads, deflections, crack widths and strains in the straps were monitored.; All the specimens showed a unique crack pattern except the specimens which were not confined. The crack pattern was very similar to the failure of the full scale bridge deck model. The ring beam provided a significant amount of confinement compared to the external steel straps. External steel straps did not contribute much to the ultimate failure load but they increased the stiffness of the specimens. Specimens confined with CFRP wrap gave more similar results compared to the PUNCH program due to the similarities in modeling. Failure predicated from the PUNCH program gave similar results to the experimental results. One objective of this research project to look for the possibility of incorporating these small scale replica models to study the failure mechanism of the steel-free bridge deck was fulfilled by comparing the PUNCH result data with the experimental results.; These experiments further proved that confinement plays an important role in punching shear failure and without confinement specimens failed from flexure. Specimens subjected to freeze and thaw cycles did not show significant amount of deterioration.