Behaviour of R.C. beams upgraded with externally bonded steel or FRP plates
The structural behaviour of simply supported reinforced concrete (R.C.) beams strengthened in flexure by externally bonded steel or fibre reinforced plastic (FRP) plates has been investigated. A novel theoretical model coupled with simple (hence, practical) procedure(s) for designing such beams against premature plate peeling failure has been developed. The theoretical model and the design procedures have been validated by an extensive number (169) of mainly large-scale test data (using steel or FRP plates) from other sources. The effects of variations in the magnitude of Young's modulus for FRP plates on the potential changes in the flexural ultimate load of R. C. beams with externally bonded FRP plates, in the absence and/or presence of plate peeling, have been investigated in some detail with the theoretical predictions of various failure loads and associated modes of failure supported by an extensive number of test results from other sources. Moreover, brief theoretical parametric studies for other first order composite beam design parameters have also been carried out in order to clarify the effects of variations in such parameters on the predicted modes of failure. It has been shown (both, theoretically and by using large scale experimental data) that the load bearing capacity for a plated beam could (under certain circumstances) be significantly lower than even that for the corresponding unplated beam with the mode of failure being of an undesirable brittle nature. Such brittle failures can obviously have serious implications in practice, where this method has been used extensively for upgrading both bridges and buildings in a number of countries, with the design calculations very often not having properly accounted for the possible occurrence of premature plate peeling phenomenon, especially when FRP plates have been used. Further work in this area included a quantitative theoretical insight into the effect of pre-cracking of the beams (under service conditions) on the ultimate plate peeling load. A critical quantitative examination of a number of previously available theoretical models, as proposed by others, has also been carried out, and some of these models for predicting the plate peeling failure of R. C. beams have been shown to suffer from rather serious shortcomings.