Numerical Study On The Pre-stressed FRP Reinforced Concrete Flexural Members

With the rapid development of civil engineering,most countries in the world have basically completed large-scale construction,and then the demand for structural reinforcement is growing.In order to ensure the original function of the structure,it is a real challenge for researchers in the reinforcement field to design a reinforcement method with high efficiency,simple operation and economic cost.FRP material is widely used in engineering reinforcement.It is a common reinforcement method to paste FRP material on the surface of tension area of reinforced concrete members for bending reinforcement.However,this method has obvious disadvantages: stress lag,low utilization of materials,and little restriction on structural cracks.Prestressed FRP material can adjust the internal force distribution of the original components,significantly improve the performance in normal use,improve the crack resistance of the structure,and effectively reduce the structural deformation and dynamic response.Therefore,in the structural reinforcement methods such as bridges,the prestressed FRP reinforcement method should be preferred.Based on the plastic damage model of concrete,the static and dynamic finite element analysis of reinforced concrete beams strengthened by prestressed FRP is carried out in this paper.The research contents and conclusions are as follows:1.A relatively mature theoretical calculation method of crack spacing is selected for analysis,which takes into account the comprehensive factors such as the bond strength of concrete and FRP cloth,the slip amount of reinforcement and CFRP cloth,and introduces the reinforcement influence coefficient to establish the calculation formula of crack spacing.Combined with the theoretical calculation method,the crack spacing of 14 FRP strengthened beams in the literature is calculated.After comparing the calculation results with the test values,it is considered that the theoretical calculation method can meet the accuracy requirements of crack spacing calculation,which provides a theoretical basis for the subsequent research on the crack suppression effect of prestressed CFRP strengthened concrete beams.2.Based on the plastic damage theory of concrete,the numerical calculation of crack spacing of reinforced concrete beams strengthened with non prestressed CFRP sheets is carried out,and the theoretical calculation formula is verified and supplemented.The interface element based on CZM(Cohesive zone model)is used to simulate the interface between CFRP cloth and concrete,and the influence of mesh size on the accuracy of calculation results is explored.The crack spacing calculated by finite element method is compared with the theoretical and experimental values,and the results show that the numerical calculation method is accurate and reasonable.3.Based on the two numerical methods of plastic damage model and XFEM,the numerical calculation and analysis are carried out for the concrete beams strengthened by prestressed FRP and non-prestressed CFRP.The load displacement curve is compared with the test value,and the reinforcement effect with or without prestressed CFRP is carried out from the aspects of bearing capacity,crack expansion,concrete stress,CFRP stress and interface stress distribution The results show that the prestressed CFRP can increase the bearing capacity of the strengthened beam more than the non prestressed CFRP,especially the cracking load,improve the rigidity of the beam,reduce the deflection,delay the crack propagation and reduce the crack spacing.4.In order to further study the effect of Prestressed CFRP on the dynamic performance of concrete beams,the finite element model of reinforced concrete beams strengthened by prestressed CFRP sheets and non prestressed CFRP sheets under impact load is established,and the transient dynamic response is calculated by using the dynamic explicit solver.The results show that compared with the experimental beams strengthened with non prestressed CFRP sheets,prestressed CFRP sheets can greatly limit the dynamic response of the strengthened beams in terms of speed,acceleration,mid span displacement,etc.,which is of great significance to improve the theoretical system of prestressed CFRP sheets.