Effects of concrete composition on the interfacial parameters governing FRP debonding from the concrete substrate

For the concrete beam strengthened with FRP, failure may occur from the bottom of a major flexural/shear crack along the span. As debonding failure occurs within the concrete, interfacial friction resulted from aggregate interlocking between opposing surfaces of the debonded zone plays an important role in the debonding behavior. Interfacial debonding can be analyzed with a three-parameter model. To investigate the effect of concrete composition on debonding behavior, the direct shear test was conducted with ten different compositions of concrete. Interfacial parameters were then derived according to a three-parameter model. The test results show little correlation between interfacial parameters and concrete compressive or splitting tensile strength. However, the debonding initiation strength and residual shear strength correlates well with the surface tensile strength and the maximum crack opening is mainly governed by the aggregate content. According to our results, the composition of the concrete is an important factor that should be considered explicitly in the investigation of FRP debonding from a concrete substrate. © 2007 Taylor & Francis Group

Mortgage Markets Worldwide

10.1002/9781444302301Mortgage Markets Worldwide1-29

Finite element study on bond behavior of steel bar and HSCC/HSFRCC

To study the bond behavior of steel bar and High Strength Cementitious Composites (HSCC) or High Strength Fiber Reinforced Cementitious Composites (HSFRCC), finite element simulations of Direct Tension Pull-out Bond Test (DTP-BT) are conducted. Default tensile strain softening relation in FE program ATENA is used to model HSCC. Satisfactory agreement between simulated and experimental load-displacement curve can be obtained by taking specific fracture energy of HSCC to be 50 N/m. Similar to experimental observations, tensile splitting failure is shown to be the dominate failure mode. To simulate the behavior of HSFRCC members, either the homogenization based approach (H-model) or individual crack based approach (I-model) can be employed to describe the tensile strain hardening behavior. In this paper, both approaches are first presented and discussed. Numerical results are compared to experimental results obtained in our laboratory. According to our findings, the pre-peak behavior of DTP-BT can be properly simulated by the I-model. On the other hand, H-model shows overestimation of pre-peak stiffness. Similar to HSCC, tensile splitting failure is the dominate failure mode of HSFRCC DTP-BT member. From the tests, the width of the splitting crack is wider at the surface than at the steel level. This can be explained by the numerical simulation which shows very high tensile stress at the surface of the DTP-BT specimen

Flexural behaviors of steel reinforced ECC/concrete composite beams

An engineered cementitious composite (ECC) is introduced to partially substitute concrete in the tension zone of a reinforced concrete beam to form an ECC/reinforced concrete (RC) composite beam, which can increase the ductility and crack resisting ability of the beam. Based on the assumption of the plane remaining plane and the simplified constitutive models of materials, the stress and strain distributions along the depth of the composite beam in different loading stages are comprehensively investigated to obtain calculation methods of the load-carrying capacities for different stages. Also, a simplified formula for the ultimate load carrying capacity is proposed according to the Chinese code for the design of concrete structures. The relationship between the moment and curvature for the composite beam is also proposed together with a simplified calculation method for ductility of the ECC/RC composite beam. Finally, the calculation method is demonstrated with the test results of a composite beam. Comparison results show that the calculation results have good consistency with the test results, proving that the proposed calculation methods are reliable with a certain theoretical significance and reference value. Single ©, including postage