Numerical Simulation Of Fatigue Failure Process For In-service Reinforced Concrete Bridge

Many bridges in-service may be subjected to fatigue loading in addition to static loads, such as vehicle load,wind load etc. The problems of bridges fatigue are paid more and more attentions. In the thesis, numerical simulations of RC bridges fatigue damage accumulation failure full-range processes were mainly studied. On the basis of the previous fatigue experiments, the thesis analylzed the rules about the degradations of both fatigue stiffness and fatigue strength, and the increase of fatigue residual strain. Accordingly the envelope equations of concrete and reinforced rebar fatigue residual strength were established, furtherly, the fatigue constitutive models of concrete and reinforced rebar in any number of times of fatigue loading were built. On this basis of the improved analytical method of the fatigue full-range, the numerical analytical method of the fatigue damage accumulation failure full-range was proposed, a example was verified by the method proposed, and the result proved the reliability of the analytical mothod. At last the method was applied to the actual bridges.The main contents are shown as following:1. On the basis of deep understanding of fatigue stiffness degradation, fatigue strength degradation and fatigue residual deformation in the process of fatigue loading, the envelope equation of concrete residual fatigue strength wered established, combined with the constitutive model of concrete under uniaxia condition, the concrete fatigue constitutive model in any number of times of fatigue loading was built.2. According to the assumption of P-M linear damage rules of effective cross-sectional area of reinforced rebar in the process of fatigue loading, the envelope equation of fatigue residual strength of reinforced reinforced steel was established, and based on the ideal elastic-plastic model of reinforced rebar, the reinforced rebar fatigue constitutive model of in any number of times under fatigue loading was built.3. Basesd on the concrete plastic damage model of ABAQUS, alculated the fatigue damage variable by applying the oncrete and reinforced rebar fatigue constitutive model. On this basis of the improved analysis of the full-range, a numerial simulation method of the full-range of RC bridges fatigue damage accumulation failure was proposed, In which the numbers of fatigue loading were simplified according to the rule of the idealized three stages of structure fatigue deformation, then. A numerical example was verified by the mothod proposed, and the result proved that numerical simulation mothod was correct and reliable.4. The load frequency value spectrum in the city of Tianjin was obtained by researching the traffic of the city, equal amplitude fatigue loading was converted by the application of the load frequency value spectrum, and made it to be applied to practical engineering; Furtherly, the mothod of inversing the maxmum of equal amplitude fatigue loading was studied in the condition of given fatigue life.