Study of the fracture behaviour of fiber reinforced concrete under direct shear loading

Abstract

The behavior of Fiber Reinforced Concrete (FRC) under Mode II of fracture is rarely reported due to the lack of information on standard testing procedures. Between the few numbers of researches performed to characterize the shear behavior of concrete, no one have dedicated to the effects of fiber orientation at different places of a concrete element subjected to second mode of fracture. In addition the efforts made on mode II loading effects are rather limited in plain concrete in general and in fiber reinforced concrete in particular. In the present study the double shear specimen (DSS) has been used to characterize the shear behavior of Fiber Reinforced Self Compacting Concrete (FRSCC). Considering the effects of fiber orientation on Mode II of fracture, some beams 150 × 150mm cross section and 60mm length has been discretized in to 8 or 12 specimens included different shear sections. Using the designed specimen, fracture energy and toughness, stress intensity factor and shear stress-slip relationship is calculated along the beams. The results show that none of the specimens are subjected to pure Mode II due to the considerable ratio of the stress intensity factors in first mode of fracture to that of the second mode "

. " Unlike the crack propagation in mode I of fracture, the shear crack propagation is accompanied by compression failure after the maximum load. The fiber bridging not only restrains the crack opening but also leads to higher interlocking. Furthermore, the dowel action of the fibers, leads to a lower slip and higher shear transfer. The suitable fracture energy and consequently high toughness is detected not only at the middle of the beam but even in the case of the specimen located at the farther distances from the center of the beam. It is indicated that using the proper Self Compacting Concrete (SCC) mix can be helpful to have the uniform shear behavior along the beam. Additionally increasing the shear plane appears to have an increasing trend in ductility, rate of fracture and toughness of the specimens. Furthermore, the orientation and distribution of fibers in concrete is investigated by the help of image analyzing. It is observed that fibers dispersed homogeneously in all concrete series. Although the density of the fibers detected on the shear plane of all the specimens is almost the same, the ductility of the specimens is different. It shows that the ductility of the specimens can be affected by the area of the shear plane.