Experimental Study On Fatigue Crack Propagation Of RC Beams Strengthened With Pre-tensioned Prestressed CFL

Carbon fiber reinforce polymer(CFRP) are well suited to strengthening engineering structures or structural members because of their high strength-to-weight ratio, good fatigue properties, and excellent resistance to corrosion. By prestressing the CFRP, the material may be used more efficiently, since a greater portion of their tensile capacity is employed. This technology has been increasing used in engineering fields recently because of the benefits such as increasing cracking load, decreasing the width of crack and improving the mechanical performances. However the theories and numerical simulation of CFRP prestressing loss in strengthening reinforced concrete is still not enough for engineering application. Besides there is limited research on the fatigue behavior of RC beams strengthened with prestressed CFRP. Therefore, there is a great significance in the theoretical research of CFRP prestressing loss in strengthening RC beams and fatigue behavior of RC beams strengthened with prestressed CFRP.Thus, this study carry out the experimental study of fatigue property and crack growth behavior of RC beams strengthened with pre-tensioned prestressed Carbon Fiber Laminate(CFL) which invented by the authors’ research group. The main research contents and conclusions in the paper are listed as follows:1) CFL was pre-tensioned with the level of prestress 8% by using tensile device developed by the author’ research group and then used to reinforce 9 RC beams. According the experimental results in research group, some measures such as pre-tensioning, releasing prestress gradually had been taken in order to reduce prestress loss of CFL. The prestress loss corresponding to the reinforcement method which has been improved is divided into five stages including stretching process, pasting process, curing process, release process and long-term loss. Inorder to study the contribution of additional U-type CFL anchor to the bond strength of interface between concrete and CFL, this paper tested the strain distribution of CFL anchor.2) In order to study the effective prestress of CFL, this paper founded the finite element models of RC beams strengthened with prestressed CFL by using the finite element softwareABAQUS. In the process of modeling, this paper considered a CFL-to-concrete interafcial constitutive model based on the experimental results of the literature[50] and the contribution of additional U-type CFL anchor. Calculated results from the developed model and experimental data show a good agreement. Also, this paper deduced the theoretical calculation formula of effective prestress of prestressed CFL reinforced RC beam of no additional U-type CFL anchor. The formula can accurately predict the effective prestress through the comparison of calculation results from modeling analysis and formula calculation.Stress intensity factor(SIF) of the main crack in reinforced beams was calculated by using the finite element method founded in this paper. The results showed that KI increased following the crack height initially. It took the maximum value when the main crack reached 30 mm height then derived rapidly.3) The main crack propagation of 8% prestressed CFL strengthened RC beams under fatigue three-point-bending loads could be described in three stages: crack initiation and quickly propagation, stable propagation and rest and unstable propagation. Fatigue life in stage II took a majority of the whole life(more than 94%). In accordance with the FEM results, a semi-empirical equation was developed to predict the crack growth rate. To validate this equation, one of the specimen was chosen to predicted the fatigue life by using this equation. The result showed that calculated fatigue life was less than the real life, which mean using this method to predict life is safe.