Hot Spot Stress Analysis Of Steel Bridge Components And Numerical Simulation Of Fatigue Damage Accumulation

This study aims at the analysis on local hot spot stress in critical components of long-span steel bridges and numerical simulation on the accumulated fatigue damage for the purpose of providing an accurate assessment of the accumulated fatigue damage and fatigue life of the components. Firstly, the analyses on the dynamical response of the Tsing Ma Bridge (TMB) under traffic loading are performed on the basis of the three dimensional finite element model of the full-scale structure of the Bridge, and some regions critical to fatigue damage are determined from the result of the dynamical response. The hot spot stress approach is usually adopted in the fatigue design and analysis of tubular welded joints. To apply the hot spot stress approach for the fatigue evaluation of long-span suspension bridges, the FEM is further used to determine the hot spot stress of the critical fatigue locations. Using the local finite element models of the welded component of TMB, typical joints are developed and the stress concentration factors are determined. These results would be able to interpret stresses at the welded sections where there are no sensors installed in the evaluation on fatigue damage by using the strain-time history data obtained from the structural health monitoring system.Secondly, the effort is made to develope new type of transition element for multi-scale fatigue damage simulaton of long-span structures for the transition between elements for the hot spot stress analysis and the structural element.The linear and piecewise linear interplotion function for displacement interplotion are used for the transition element formulation according to the displacement compatibility requirement between element interfaces. The incompatible displacement mode is introduced in the displacement interplotion and the method is used in the patch test for the element. Two numerical examples of simple component in two and three dimensions are analyzed respectively by using the formulated transition element. The calculated results show that the formulated transition element can realize the transition between elements with different mesh densities and the calculated stress has a higher precision, which suggests that the transition method using the formulated two dimensional and three dimensional transition element is feasible for the transition between different meshes of elements in the multi-scale damage modeling.To validate the formulated transition element for the calculation of the hot-spot stress and stress concentration factor in the welded components by experimental results, the stress concentration factor of the experimental welded specimens carried out in the research group is calculated by using the developed plane-transition element. The calculated stress concentration factor in the two types of tested welding components agrees well with that obtained from the experimental result. And the calculated result on the tendency of hot-spot stresses agrees well with that from the measured result. The formulated transition element and the corresponding results provide an useful tool for practical analysis of engineering structures.Thirdly, the finite element analysis full-coupled fatigue damage evolution is implemented on the basis of the user interface of the finite element software ABAQUS. The full-coupled method developed with damage mechanics and the finite element analysis is performed on calculation of fatigue damage accumulation of the critical welded components in the Tsing Ma Bridge. The calculated result shows that the fatigue damage in the critical welded components is accumulated in the region of toe of welding. The value of faitgue life calculated by the full-coupled method is smaller than that by the uncoupled method, which suggests that there exists interactionbetween the fatigue damage evolution and the structural response. The linear Miner's Law is widely used however conservative for the evaluation of fatigue life of bridge on service so that it is unfavorable for accurate assessment of fatig...