SLIPPAGE OF STEEL IN ENGINEERED CEMENTITIOUS COMPOSITES AND NORMAL STRENGHT CONCRETE

Abstract

The possibility of composite action of reinforced concrete member is dependent on the existence of sufficient
bond strength between concrete and steel reinforcing bars that in turn helps to effectively transfer shear stress between
the two. The relationship between bond strength and compressive strength of concrete is directly proportional, thereby,
higher concrete strength means higher bond strength. Therefore required development length can be reduced.
Experimental investigations were carried out to evaluate the impact of development length on bond stress and slip
relationships. For this purpose, casting and testing of 24 pull-out samples, comprising of equal number of high and
normal concrete strengths, were carried out. As a result of the experiments, it was empirically found that bond strength
increased for both high and normal strength concrete when development length was increased from 5db to 10 db as
shown in figure Figure 11, 12 and 13. However, in case of normal strength concrete increase in bond strength is more
compared to that in high strength concrete as it is clear from Figure 11 and Figure 13. The increase in bond strength is
observed even at 10db development length but the extent is less for 19 mm than 16 mm bars as shown in Figure 12 and
Figure 13. This is in agreement with the earlier findings of Chen et al and Harajli et al. However incase of HSC the total
slippage at 10db is 50% greater than at 5db. This may be due to the fact that more no of concrete keys participate in
resisting the slippage.