REINFORCED CONCRETE BEAMS UPGRADED WITH EXTERNALLY BONDED STEEL OR FRP PLATES

The present paper reports the salient features of a semi-empirical model which throws some light into the appropriate model of steel or FRP plate peeling failure, and the outcome of which is supported by an extensive set of mainly large scale test data from other sources. Based on this model, the premature plate peeling failure is controlled by the spacings of stabilised cracks in the concrete cover zone, and due to large variations (by a factor of, say, 2) in such crack spacings in practice, it is concluded that a unique solution for the plate peeling failure load does not exist, and one has to resort to upper/lower bound approaches, with the lower bound predictions being the appropriate (ie safe) ones for design purposes. Furthermore, in view of the lack of a unique solution, it may be argued that the previous general practice among various researchers who have (over a number of years) carried out purely experimental parametric studies has been fraught with difficulties and uncertainties with the wide scatter problem making any conclusive deductions based on purely experimental comparisons very difficult if at all possible. Finally, it has been demonstrated both theoretically and by using extensive large scale test data, as reported by others, that if the practising engineers do not guard against the potentially dangerous brittle steel plate ultimate (failure) moment of the corresponding unplated (ie original) RC beam which has been designed according to the ultimate limit state code recommendations even when (unlike the plated beam) material partial safety factors are included in the design calculations for the unplated beam. This observation may have significant practical implications, particularly when one considers that the method of strengthening RC beams with externally bonded plates has already been used extensively, in a number of countries, for upgrading both bridges and buildings. (A) For th e covering abstract see ITRD E106406.