Theoretical and experimental study on externally plated R.C. beams

Using theoretical parametric studies, based on a recently proposed model, the influence of various design parameters such as concrete cube strength, size and position of main embedded tensile bars, width of the beam, plate thickness, and ratio of plate/beam width, on the magnitude of ultimate plate peeling moment are investigated and some aspects of the theoretical predictions are checked against large scale test data reported by others. The theoretical model depends on the spacings of stabilized flexural cracks in the concrete cover zone, and in view of large variations (by a factor of, say, 2) in the spacings of such cracks in practice, it is argued that a unique solution for the ultimate plate peeling moment does not exist and, hence, one has to resort to theoretical upper/lower bound solutions. Moreover, the question of pre-cracking of the beams prior to upgrading them with externally bonded steel plates is discussed in some detail. It is theoretically shown that testing uncracked (i.e. as cast) beams provides results which may reasonably safely be used for predicting the behaviour of actual beams in practice which (under service conditions) are invariably pre-cracked to some degree. Finally, it is shown that if the practising engineers do not guard against the potentially dangerous brittle premature plate peeling failures, the ultimate plate peeling loads can be significantly lower than the associated ultimate (failure) loads of even unplated R.C. beams which have been designed according to the ultimate limit state code recommendations even when partial material safety factors are included in the design calculations of the unplated beams.