Amorn Pimanmas

pp. 1039 - 1048

Abstract

The effect of pre-cracking on the behavior and failure mode of reinforced concrete beams damaged by pre-cracking is experimentally studied in this paper. The control beam was designed to fail in ductile flexural yielding under four-point bending and in brittle shear under three-point bending. The effect of precracking is studied under both four-point bending and three point bending. In the former, pre-cracks are inclined with respect to the beam axis and the shear span is short, hence the external load is resisted by diagonal compression strut. In the latter, pre-cracks are orthogonal to the beam axis and the shear span is moderately long, hence the external force is transferred through concrete tensile strength, i.e., shear in moderately slender beam. The tests under these two load conditions therefore cover the effect of pre-cracking on concrete under compression and tension where the mode of load resistance is different. It is shown that when the shear span is short, pre-crack reduces the shear crushing capacity due to the reduction in effective
contact area and compressive strength deterioration due to micro-fracturing damages. The presence of precracks can change the failure mode from ductile flexure to brittle shear. On the other hand, when the shear span is longer, pre-crack elevates the shear capacity through crack arrest mechanism. In both cases, the precracking is demonstrated to be structurally significant and should be properly taken into account when analyzing existing members.