Study On Vibration Characteristics Of Cracked Reinforced Concrete Beams Under Vehicle Load

The number and size of bridges in China is ranked No.1 in the world,and the number of highway bridges alone is close to 800 thousand at present.At the same time,the number of bridges in maintenance period is increasing,and more than 100 thousand bridges are dangerous bridges.Reinforced concrete bridge is the main bridge of small and medium span bridges in our country,which may crack due to overloading,design mistakes and natural disasters in the course of operation.Cracks in the bridge will affect bridge's performance,and the effect of cracks will be enlarged by the vehicle load.The cracked reinforced concrete simply supported beam bridge is the research object in this thesis,and the vibration performance and crack propagation performance of the cracked bridge under vehicle load are studied,Which Can be used as the theoretical foundation for damage identification and damage assessment of cracking bridges.The main work includes:1.Based on the fracture mechanics theory,the variable stiffness model of concrete is established by setting the threshold of the strength of the concrete crack.The model can be used in finite element modeling to consider the nonlinear characteristics of fracture by using spring element.2.By comparing different breathing crack model,it is found that the nonlinearity of the breathing crack will lead to the sub harmonic vibration of the beams.The change of the frequency amplitude of the sub harmonic vibration can be used to establish the relationship between the vehicle load and the damage degree of the bridge,then identification of cracks in concrete beams can be implemented.3.The method that combines Vehicle-bridge coupling vibration analysis with the interaction integral is used to solve the 3D dynamic stress intensity factor,and this method can consider the effect of inertia.4.Study of the different condition in cracked reinforced concrete simply supported T beam shows that the vehicle load,road irregularity and damage degree has great influence on the crack propagation performance,and the structural damping,vehicle speed and crack shape has little influence on the crack propagation performance.