Influence of Toughness on the Apparent Cracking Load of Fiber-Reinforced Concrete Slabs

It is widely believed that the onset of flexural cracking in a fiber-reinforced concrete (FRC) slab is governed by the modulus of rupture (MOR) of the concrete matrix and that the peak in load resistance associated with cracking of the concrete matrix in bending is independent of postcracking behavior. This model of flexural resistance underpins most methods of thickness design for concrete slabs-on-grade and other concrete plate elements subject to point loading. The present investigation has demonstrated that the peak in load resistance associated with cracking of a FRC slab in bending cannot be determined as a simple function of the MOR alone. Experimental results have indicated that plasticity in the immediate postcrack range can influence the peak in load resistance associated with cracking, even if the MOR is unchanged. The present results also suggest that the method of structural analysis used to design concrete slabs should be governed by the degree of strain softening or plasticity exhibited by the material in the immediate postcrack range.