Theoretical and experimental study on externally plated RC beams

Using theoretical parametric studies, based on a recently proposed model, t he influence of various design parameters such as concrete cube strength, s ize and position of main embedded tensile bars, width of the beam, plate th ickness, and ratio of plate/beam width, on the magnitude of ultimate plate peeling moment are investigated and some aspects of the theoretical predict ions are checked against large scale test data reported by others. The theo retical 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 s olution for the ultimate plate peeling moment does not exist and, hence, on e has to resort to theoretical upper/lower bound solutions. Moreover, the q uestion of pre-cracking of the beams prior to upgrading them with externall y bonded steel plates is discussed in some detail. It is theoretically show n that testing uncracked (i.e. as cast) beams provides results which may re asonably safely be used for predicting the behaviour of actual beams in pra ctice which (under service conditions) are invariably precracked to some de gree. Finally, it is shown that if the practising engineers do not guard ag ainst the potentially dangerous brittle premature plate peeling failures, t he ultimate plate peeling loads can be significantly lower than the associa ted ultimate (failure) loads of even unplated R.C. beams which have been de signed according to the ultimate limit state code recommendations even when partial material safety factors are included in the design calculations of the unplated beams. (C) 1999 Elsevier Science Ltd. All rights reserved.