Study On Flexural Behavior Of Concrete Beam Strengthened With Prestressed CFRP Fabric Under Variable Overload

As a novel high-strength and high-performance structural material, CFRP exhibits enormous application prospect in reinforcement of bridge structures. In consideration that auto loads on bridge structures are in general cycle loads at variable amplitudes and no rules are followed for its load history, so fatigue stress characterized by variable amplitudes, high cycle and randomness is produced. Therefore, this paper studies the bending resistance of the prestressed CFRP reinforced beams under the effect of variable amplitude overload and puts emphases on fatigue test and theoretical analysis for fatigue life of the CFRP reinforced beams under the effect of cycle loads.Main missions and achievements of this paper are as follows:Study the performance of FRP material and application methods of prestress, and carry out the bending test for the prestressed CFRP fabric reinforced concrete beams, discuss the mechanical features of reinforced beams, and investigate influences of factors such as amount of reinforcement of CFRP fabric, degree of prestress and anchoring methods, etc. on bearing capacity of the prestressed reinforced concrete beams.Apply loads at the amplitudes of0.7,0.8and0.9times the ultimate bearing capacity to the CFRP fabric reinforced concrete beams respectively to simulate the effects of over-load vehicles on bridges. Collect mechanical parameter data of beams under the effect of overload, record the development of cracks of beams, discuss influences of overload on bearing capacity and deflection of the reinforced beams and its roles in production and development of cracks of the reinforced beams, and give corresponding laws.Discuss fatigue crack propagation life of the CFRP reinforced beams under the effect of cycle at constant amplitude by means of the fracture mechanics theory, obtain the prediction model for fatigue crack propagation life of the reinforced beams under the effect of cycle loads at variable amplitudes, establish the relation between fatigue strength at constant amplitude and fatigue strength at variable amplitudes, and realize checking calculation for fatigue of the CFRP reinforced beams under the effect of cycle loads at variable amplitudes. Based on the measured traffic traffic flow data for statistical analysis features, combined with the Wiener-Khintchine formula stationary process autocorrelation function, the control standard power spectrum function fitting, deduced autocorrelation function and power spectral density function suitable for the actual traffic flow. Achieve the numerical simulation of the actual traffic flow about variable amplitude cyclic effect of Shenyang city highway Hou ding-xiang bridge to provide the appropriate numerical simulation cyclic loading test sequence.Carry out the fatigue life test for the CFRP fabric reinforced beams under the effect of cycle loads at variable amplitudes, calculate crack propagation rate by means of the above prediction model for fatigue crack propagation life of the reinforced beams under the effect of cycle loads at variable amplitudes, conduct checking calculation for fatigue of the reinforced beams and verify correctness of the theory.