Mechanical behavior of the asphalt wearing surface on an orthotropic steel bridge deck under cyclic loading

Orthotropic steel decks are prone to fatigue problems and to delamination of the wearing surface. In addition, the mechanical behavior of the asphalt wearing surface on an orthotropic steel bridge deck is viscous and affected by the amplitude and frequency of moving loads. This paper presents an experimental investigation on the strain distribution and evolution in an orthotropic deck under cyclic loading. A five-point bending (5PB) test was used in this study. The tested orthotropic deck was composed of a 14-mm-thick steel plate, an epoxy bonding layer, and a 7-cm-thick epoxy asphalt mixture layer. Two types of tests performed at a fixed temperature were: i) cyclic loading with a small number of cycles at different frequencies and loading amplitudes, and ii) fatigue test. The strain was measured at different positions in the steel plate and in the asphalt wearing course. The results obtained from the first type of tests show the strain distribution in the orthotropic deck and the effect of frequency and loading amplitude on this distribution. When the loading amplitude varied from 20 kN to 40 kN, the behavior of the deck structure was observed to be quasi-linear except for several points in the asphalt wearing course where the strain amplitude was higher than 1000 µm/m. The viscoelastic property of the epoxy asphalt concrete was shown to have a significant influence on the deformation of the deck structure. During the fatigue test, the effect of the cyclic loading on the strain evolution in the orthotropic deck was analyzed. The results show that the accumulated strain in the steel plate was small and reversible while that in the asphalt wearing course was important and irreversible, which caused the cracks and damage in the specimen. Fatigue cracking at the top of the asphalt concrete layer and the debonding of the asphalt concrete layer from the steel plate at the support positions were also observed during the fatigue test.