Hot spot stress approach for fatigue evaluation using finite element method

Fatigue design rules commonly used in practice are mainly based on the nominal stress approach. An alternative method for the complicated welded steel joints fatigue design is the hot spot stress approach. To apply the hot spot stress approach for fatigue evaluation of long span suspension bridges, a finite element method is used to determine the hot spot stress of critical fatigue locations. Using the local finite element models of the Tsing Ma Bridge, typical joints are developed and the stress concentration factors are then determined. 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 the online health monitoring system installed on the Tsing Ma Bridge. A comparison is made between the nominal stress approach and the hot spot stress approach for fatigue life evaluation of the Tsing Ma Bridge. The comparison result shows that the hot spot stress approach is more appropriate for fatigue evaluation.