Life cycle evaluation of fatigue mitigation for orthotropic steel bridge decks

Abstract

Bridges with orthotropic steel decks have been built across the world over the past 60 years because they provide high strength and stiffness at a relatively low cost. However, a number of these bridges have sustained fatigue fractures. The investigation described in this thesis was carried out in order to identify cost-effective fatigue crack mitigation techniques by using the deck surfacing to reduce the stresses in the steel deck. Epoxy asphalt with an expanded metal mesh was investigated with small- and large-scale laboratory tests. Finite element analyses were also performed. The small scale tests conducted at different temperatures and loading frequencies showed that asphalt stiffness increased with decreasing temperature and faster loading. The expanded metal mesh in the epoxy asphalt layer noticeably increased asphalt stiffness. In the large scale tests and finite element analyses, critical loading positions to cause stress concentrations at the fatigue prone rib-to-deck welded connections were determined with different tyre configurations. The stress reduction due to the deck surfacing was estimated for the critical loading positions. The full scale test specimen was subjected to actual truck tyres. With the effectiveness of mitigation techniques for fatigue cracks on orthotropic steel bridge decks known, a probability-based fatigue lifetime evaluation methodology using Monte Carlo simulation was developed. The deck surfacing effects with seasonal and hourly temperature variations were considered. The fatigue lifetime extension using the epoxy asphalt was quantified. For a particular bridge, cost-effective maintenance scenarios were investigated. A simple calculation method for fatigue lifetime was introduced for engineers or bridge owners to assist understanding of decision support tool concepts.