AN INVESTIGATION OF DOWEL ACTION IN REINFORCED CONCRETE BEAMS

Abstract

Inspite of many decades of intensive experimental as well as analytical research the phenomenon of shear resistance of reinforced concrete beams is yet to be conclusively understood. Of the four mechanisms of shear resistance in a web-reinforced R. C. beam viz. (i) shear resisted by uncracked concrete in the compression zone (ii) shear resisted by aggregate interlock (iii) shear resisted by dowel action and (iv) shear carried by web reinforcement, there is a considerable debate on the role of the mechanisms of aggregate interlock and dowel action in the shear capacity of a R. C. beam. It has been suggested in the literature that the contribution of the longitudinal tension reinforcement in the dowel action mechanism is through shear, kinking and bending. Such a hypothesis implies that the amount of tension reinforcement as well as the diameter of the tension reinforcement should have a significant influence on the dowel action. The effect of the following three parameters on the mechanism of dowel action has been experimentally investigated: (i) Amount of tension reinforcement (ii) Rebar diameter for a given amount of tension reinforcement and (iii) shear span-to-depth (aid) ratio. The experimental results indicate that both the amount of tension reinforcement as well as the rebar diameter have only a marginal effect on dowel resistance and insufficient experimental support was observed for the strong dependence of shear strength on the amount of tension reinforcement given in current design codes. The results of this study show that the bar diameter has an insignificant effect on the load carrying capacity of R.C. beams which suggests that dowel action is unlikely to be a significant factor in the internal load — transfer mechanism of such beams.