| ECC, short for engineered cementitious composites, is a kind of fiber reinforced cementitious composite material which exhibits ultra-high toughness and superior crack control ability. ECC with 2% PVA fiber in volume shows an ultimate strain from 2% to 6%, with the properties of pseudo tensile strain-hardening and multiple cracking. ECC is further characterized by outstanding shear properties, with much higher shear strength and ductility than conventional concrete, which could effectively decrease brittleness of the concrete structure. ECC combined with FRP, which is characterized by lightweight, high strength, high corrosion resistance and superior workability, provide a practical solution to the problem of structural durability in harsh environments. Due to the higher cost than conventional concrete, ECC is always cast with concrete forming ECC/RC composite beam, which obtains relatively higher performance price ratio. In this paper, shear behavior of FRP reinforced ECC beams and ECC/concrete composite beams are investigated through experimental study, numerical simulation and theoretical analysis.The Ohno shear beam configuration was chosen to test the shear behavior of three kinds of PVA-ECC with different strength. Based on test results, a simplified shear constitutive model was proposed. The results showed shear stress-strain relationship curves of concrete were linear elastic without plastic. On the contrary, curves of ECC showed double-linear and pseudo strain-hardening properties. The proposed shear constitutive model showed good agreement with test results, indicating that it is able to demonstrate shear properties of ECC.Six BFRP reinforced ECC beams, tow ECC/concrete composite beams and one concrete beam with different materials, stirrup ratios and shear-span ratios were performed through a four-point bending test. Experimental results showed that compositing ECC on the bottom of beams was more efficient than on the top for composite beams.95% of shear properties of ECC beams could be reached when compositing ECC on the bottom with the thickness of 30% beam height. For ECC beams, the brittle performance would be improved by excessive stirrup ratios. And appropriate stirrup ratios for ECC beams seemed to be 0.24% and 0.32%. Comparatively high shear strength and shear durability was achieved when shear-span ratios of ECC beam were 2.5.Shear behaviors of BFRP reinforced ECC beams, ECC/RC composite beams and concrete beams were analyzed based on the software of ATENA. The test results were matched well by simulated load-displacement curves. Further, the influences on shear behavior of shear-span ratios, position and thickness of ECC layer and tensile properties of the ECC were discussed. The simulation results showed that the failure mode of BFRP reinforced ECC beams turned from shear compression to shear tension, and finally to flexural failure with the shear-span ranging from 2.08 to 3.21. Compared to concrete beams, deformation performance of composite beams was significantly improved when ECC layer was placed on the top. But the promotion showed no obvious relationship with the thickness of ECC layer. On the other hand, shear strength and durability of composite beams were both improved owing to the ECC layer on the bottom. And the promotion increased with the growth of the thickness of ECC layer. Shear properties of ECC beams were also influenced significantly by tensile properties of the ECC. But after peak tensile strain reaching 3%, the shear properties of ECC beams almost could not be enhanced by perfecting tensile properties of ECC material.On the base of truss-arch model, an expression to predict the shear strength of shear-critical ECC beams is presented, which considers the contribution of tensile stress of ECC on the position of diagonal cracks. The compared result between test data and calculated results showed that the proposed expression provides a satisfactory accuracy on shear strength predictions of ECC beams with stirrups. |
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