Papers by Author: Tommy Hung Tin Chan

Abstract: The finite element analysis fully coupled fatigue damage evolution is implemented on the user subroutine UMAT of the finite element software ABAQUS. The fully coupled method developed with damage mechanics and the finite element analysis is performed on calculation of fatigue damage accumulation of the critical welded member in the Tsing Ma Bridge. The calculated result shows that the fatigue damage in the critical welded member is accumulated in the region of toe of welding. The value of faitgue life calculated by the fully coupled method is smaller than that by the uncoupled method, which suggests that there exists interaction between 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. The above results provide feasible method for accurate evaluation of fatigue damage in bridge components based on the hot spot stress analysis and the damage mechanics theory.

Abstract: The suspension bridge has more flexibility and repetitive vehicles produce stress cycles in members. Then fatigue of the member is accumulated with the daily traffic loadings. In order to evaluate the working condition of the Tsing Ma Bridge, the online monitoring health system has been installed in long suspension bridge. The location of the strain sensor is not exactly at the critical member locations. The hot spot stress analysis for critical members is necessary for accurate fatigue evaluation of the bridge. The global finite element analysis of the Tsing Ma Bridge under traffic loading is performed to determine the critical fatigue member locations. A detailed local finite element analysis for the welded connections is performed to determine the hot spot stress of critical fatigue location. As a case for study, the calculated stress concentration factor is combined with the nominal representative stress block cycle to obtain the representative hot spot stress range cycle block under traffic loading from online health monitoring system. The comparison result shows that the nominal stress approach cannot consider the most critical stress of the fatigue damage location and the hot spot stress approach is more appropriate for fatigue evaluation.

Abstract: The crack growth behavior and the fatigue life of welded members with initial crack in bridges under traffic loading were investigated. Based on existed fatigue experiment results of welded members with initial crack and the fatigue experiment result of welded bridge member under constant stress cycle, the crack keeps semi-elliptical shape with variable ratio of a/c during crack propagation. The calculated method of the stress intensity factor necessary for welded bridge member crack propagation was discussed. The crack remained semi-elliptical shape with variable ratio of a/c during crack propagation. The fatigue crack propagation law suitable for welded steel bridge member fatigue crack propagation analysis was deduced based on the continuum damage mechanics and fracture mechanics. The proposed fatigue crack growth model was then applied to calculate the crack growth and the fatigue life of existed welded member with fatigue experimental result. The calculated and measured fatigue life was generally in good agreement, at suitable initial conditions of cracking, for welded member widely used in steel bridges.

Abstract: The behavior of crack growth with a view to fatigue damage accumulation on the tip of cracks is discussed. Fatigue life of welded components with initial crack in bridges under traffic loading is investigated. The study is presented in two parts. Firstly, a new model of fatigue crack growth for welded bridge member under traffic loading is presented. And the calculate method of the stress intensity factor necessary for evaluation of the fatigue life of welded bridge members with cracks is discussed. Based on the concept of continuum damage accumulated on the tip of fatigue cracks, the fatigue damage law suitable for steel bridge member under traffic loading is modified to consider the crack growth. The proposed fatigue crack growth can describe the relationship between the cracking count rate and the effective stress intensity factor. The proposed fatigue crack growth model is then applied to calculate the crack growth and the fatigue life of two types of welded components with fatigue experimental results. The stress intensity factors are modified by the factor of geometric shape for the welded components in order to reflect the influence of the welding type and geometry on the stress intensity factor. The calculated and measured fatigue lives are generally in good agreement, at some of the initial conditions of cracking, for a welded component widely used in steel bridges.