Optimizing the assessment of fatigue in inverted T-girder bridges

Abstract

With the continuous increase in transportation volume, bridges face the challenge of carrying higher traffic loads. As a result, bridges undergo fatigue due to repeated and increasing loads, leading to progressive deterioration of their structural reliability. While existing codes already account for several variables affecting the concrete's ability to withstand compression fatigue, some critical factors are still not considered. Furthermore, the modelling aspects of Finite Element Analysis (FEA) are often simplified or disregarded in practical applications, leading to an inaccurate estimation of fatigue life for concrete. As a result, a considerable number of bridges may be rejected for fatigue despite the possibility that they are not susceptible to this issue.
To address these issues, this thesis presents a parametric study that explores and quantifies the influence of various parameters on the fatigue life of inverted T-girder bridges, focusing on modelling aspects and material degradation. For this reason, a special case study was specifically designed to fail in fatigue within its lifespan. The fatigue analysis process employed both analytical and numerical methods, with the fatigue failure of the beams determined based on the bending failure at the beam's midspan criterion. A basic case was established as a basis for analysis, and the effect of each parameter was evaluated by incorporating it into the basic case and calculating the fatigue life of the bridge.
The analysis results demonstrate that stress distribution affecting parameters are significantly important in determining the fatigue performance of a bridge. The analysis identified that accounting for the gradual development of prestress losses, rather than instantaneous losses, and utilising area loads for vehicle modelling are critical aspects that substantially prolong the bridge's fatigue life. Furthermore, performing a historical lane configuration analysis is crucial for accurately assessing fatigue, as it significantly impacts the fatigue life of the bridge and identifies its critical components. The inclusion of material degradation caused by cyclic loading in the fatigue analysis is highly advantageous. It can even result in the bridge no longer being susceptible to fatigue. It is worth noting that accounting for the cracking of the slab in the lateral has a major negative effect on the fatigue life of the bridge. However, it is necessary to include it in the analysis to avoid an inaccurate and overly optimistic fatigue assessment. The study also provides specific equations to calculate the effect of time-dependent traffic volume on fatigue life. Lastly, the research investigated other parameters, such as the composite action of the structural components, which had a minor effect on the fatigue life of the bridge.
It is important to note that the influence percentage of most parameters cannot be generalised to all bridges, as they are contingent on specific factors unique to each case. Nevertheless, this research provides insights into the magnitude and contribution of the investigated parameters' effect on the fatigue life of concrete bridges, outlining those that must be necessarily included in the fatigue assessment.