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.
In this paper, four point bending tests were carried out to investigate the flexural properties of PVA fiber reinforced engineered cementitious composites (ECC) with different mix proportions. Based on the test results, the flexural toughness was evaluated with the methods of JSCE and post crack strength method (PCSm), respectively. Several parameters such as amount of water reducer, amount of sand, and fiber volume fraction were investigated to study their effects on the flexural toughness of ECC beams. According to the test results, superfluous water reducing additions can cause adverse effect on strength of the matrix and interfacial bond between fibers and the matrix, resulting in decreased bending strength and flexural toughness of ECC beams. Increase of the fiber volume fraction can result in increased flexural strength and toughness due to enhanced bridging effect between fibers and cementitious matrix. High amount of sand can reduce ductility and strain hardening behavior of ECC material, and better flexural toughness can be achieved when the amount of sand by weight is set to 0.2 for current water/cement ratio.
External bonding of fiber reinforced polymer （FRP） composites on the concrete structures has been proved to be an effective and efficient way to strengthen concrete structures. For a FRP strengthened concrete beam, it is usually observed that the failure occurs in the concrete and a thin layer of concrete is attached on the surface of the debonded FRP plate. To study the debond behavior between concrete and FRP composites, an analytical model based on the three-parameter model is developed to study the debonding behavior for the FRP-to-concrete joint under pure shearing. Then, nonlinear FEM analysis is conducted to verify the PrOposed analytical model. The FEM results shows good agreement with the results from the model. Finally, with the analytical model, sensitivity analyses are performed to study the effect of the interracial parameters or the ~eometric parameters on the debondin~ behavior.
