Experimental Investigation of the Effect of Curtailed Reinforcement on the Shear Failure of RC Members Without Stirrups

Abstract

Curtailing of reinforcement in concrete beams and slabs is often carried out in practice for different reasons; in continuous beams, top reinforcement is often curtailed in accordance with the extent of the hogging moments and generally, in concrete structures it is often necessary to add extra reinforcement for practical reasons, which is normally considered to be safe.

It is generally accepted that the shear capacity of concrete members without stirrups is influenced by factors such as the crack width. On the other hand, it has been up for discussion how curtailed reinforcement may influence the crack width and the failure mechanism. In the fib Model Code for Concrete Structures 2010 the shear capacity decreases in a zone near the curtailed end of reinforcement bars. In some practical design situations, this means that adding extra reinforcement with curtailed ends would decrease the shear capacity. This influence is not even mentioned in Eurocode 2.

This paper presents a large experimental programme dedicated to study the influence of curtailed reinforcement on the shear capacity. The programme includes 30 simple three-point bending tests of beams governed by shear failure. The main parameters varied in the tests are the relative amount and the length of the curtailed reinforcement. The tested shear capacities show that the shear capacity was not affected.

During tests, Digital Image Correlation was used to measure the crack propagation. From these measurements, it appeared that the curtailed reinforcement had no influence on the crack widths nor on the observed failure mechanisms.

Finally, the tested shear capacities are compared to shear capacities calculated by the Eurocode 2 and the fib Model Code 2010. While Eurocode 2 is quite accurate, the fib Model Code 2010 underestimate the shear capacity.