Longitudinal shear strengthening of composite bridge beams

A number of composite concrete bridges (i.e. bridges with precast prestressed concrete beams designed to act structurally in combination with a cast-in-situ concrete slab) were constructed in Western Australia in the 1960s and 1970s. Newer editions of bridge design codes have altered the requirements to which these bridges were designed. Recent assessments made on the basis of the new requirements have indicated that these structures exceed current stress limits in longitudinal shear and therefore need strengthening. To implement effective non-destructive retrofit strategies, Main Roads Western Australia (MRWA) initiated a testing programme to investigate the application of non-intrusive strengthening schemes comprising epoxy-bonding of carbon-fibre reinforced polymer (CFRP) and glass-fibre reinforced polymer (GFRP) products to reduced-scale specimens representing the connection between concrete elements in a bridge deck. A total of 32 specimens were tested. The tests were specifically designed to assess the strength of the connection under the small deformations generated in bridge decks under service conditions. The performance of the tested specimens has been compared in terms of relative slip and separation between the connected concrete blocks at peak force. The results have provided insight into the key variables that govern the strength of retrofitted connections under longitudinal shear (e.g. concrete roughness at the interface, concrete strength, reinforcement at the interface, anchorage/bonding, fibre direction, weaving pattern and thickness of the epoxy-bonded fibre composites). While the results were obtained for a specific Australian problem, they might have application to similar situations elsewhere.