Fatigue Life Evaluation of Suspenders on a Continuous Suspension Bridge Subject to Various Wind and Traffic Load Levels

As the main force-transmitting component of the continuous suspension bridge, the suspender system is extremely susceptible to fatigue damage caused by wind and traffic loads. Displacement-controlled device (DCD) and load level, as important factors affecting structural fatigue life, are usually ignored in previous studies. Combined with a monitoring technique, a fatigue life evaluation framework for the suspender system of the continuous suspension bridge is proposed, including the modeling of wind and traffic loads and the analysis method of structural dynamic response. A case study was conducted on a typical continuous suspension bridge with DCD. The influence of load level and DCD on the fatigue life of the suspender system was analyzed in detail, and the linear prediction model of the fatigue life under various load levels was given. The results show that the absence of DCD will cause the relative damage index of the structure to exceed the safety threshold, and the suspenders may even fail due to fatigue within the designed service life. In pace with the mean wind speed and traffic density increase, the fatigue damage of the suspender gradually rises, and the linear model can perfectly predict the fatigue life under different load levels. Fitting results revealed that the fatigue life of the long suspender is more sensitive to the wind-load level, while the fatigue life of the short suspender is greatly susceptible to the variation in traffic loads. The effect of bending stress on the long suspender is relatively limited, but it is significant on the short suspender because of the large relative displacement between the main cable and girder. This is the main reason that fatigue life of the short suspender is generally lower than that of the long suspender.