Fatigue damage of suspenders is a main concern during the life-cycle maintenance of arch bridges and suspension bridges. This paper presents a practical framework for estimating the fatigue life of suspenders under repeated traffic loads by taking a three-pylon suspension bridge as an example. First, the basic theory of vehicle–bridge interaction (VBI) is introduced and a finite element model of the bridge structure is established. Second, the fatigue load spectrum is defined in detail based on the analysis of WIM (weigh-in-motion) data. And then, parametric analysis is carried out to clarify the influence of road roughness, vehicle speed, and driving lanes. Among which, the time-dependent stress laws are simulated according to the defined fatigue load spectrum and the stress range is counted through the Rain flow counting method. At last, the fatigue life of uncorroded suspenders and naturally corroded suspenders is estimated by an S–N curve and Miner cumulative damage criterion. Results reveal that the fatigue life of suspenders is more than 100 years if no corrosion happens, while less than 20 years for short suspenders considering the influence of natural corrosion.

This paper presents a multi-scale approach to predict the macro-crack initiation life (MCIL) of welded joints. This fully adaptive multi-scale technique is designed to take into account micro-scale material heterogeneity due to the existence of defects and to consider the uncertainties regarding defect occurrence and characteristics and traffic loading. The procedure of the proposed approach was introduced along with an orthotropic steel deck. Firstly, a homogenisation method was used to link defects in the heat-affected zone with the macro-scale structure. This allows for estimating the effective Paris constant, required for a Paris Law-based fatigue damage analysis. Secondly, a traffic flow, based on weigh-in-motion measurements, was used to simulate the load effects on the examined joint. Afterwards, the extended finite element method was adopted to calculate the stress intensity factors with respect to the weld geometries. Finally, the damage before macro-crack initiation was obtained using the Paris Law. In addition, Monte Carlo simulation was integrated within this multi-scale crack growth procedure to consider the randomness in pore and inclusion occurrence and characteristics. Hence, the MCIL is expressed in the form of a probability distribution. Results show that the proposed approach enables to provide a rational maintenance and inspection intervention time.