Optimized Design Of Anti-Fatigue For The New Type Of Orthotropic Steel Bridge Decks

The orthotropic steel bridge deck has been applied widely because it has high ultimate bearing capacity, light weight and is easy to manufacture and install. But the structure appeared many fatigue cracks during use. They influenced the performance of the bridge seriously. To improve the fatigue performance of orthotropic steel deck, the main work and the corresponding conclusions are as follows:(1) Through the investigation of the fatigue damage of orthotropic steel deck, it was found that there are four parts more prone to appear fatigue cracks. The related research results at home and abroad are summarized. In order to improve fatigue performance of the structure, some scholars abroad forwarded the new type of longitudinal rib structure.(2) The fatigue damage mechanism of damageable parts is analyzed. In view of the orthotropic deck mechanical characteristics, it was pointed out that the fatigue crack is outcome of combined action of load and the deformation. Design parameters and structural details have important effects on fatigue performance of the key positions.(3) Two new large longitudinal rib patterns and the traditional longitudinal rib of orthotropic plate finite element model are established. Loading positions are moved along the horizontal and vertical. Fatigue stress amplitude and the deformation outside face of the key points are compared. Analysis results show that a greater vertical deflection appeared in the welds of roof-to-rib of new type of orthotropic bridge decks. And it produced greater stress amplitude, has poor fatigue performance, so further optimized is needed. As to the welds of diaphragm-to-rib detail and grooving of diaphragm, their outside parts of the surface deformation and stress amplitude has no obvious relation. But the 400mm longitudinal rib has a better fatigue performance and the minimum stress amplitude.(4) Based on stress amplitude and the deformation outside face, design parameter and structural details of the new type of orthotropic bridge decks are optimized. At the same time, the relationship between stress and surface deformation is discussed Analysis results show that vertical flexure deformation of cover plate and D1, D2 and D3 point stress amplitude decrease with the increase of the thickness of plate. The thickness of diaphragms has no obvious influence for deformation and stress amplitude. Increasing the thickness of the longitudinal rib is beneficial, and the distance between diaphragms increased from 4 m to 8 m, the deflection of the mid-span increased 2 times. The vertical deflection of roof is reduced obviously by joining at the top of the small plate. The stress amplitude is decreased by 72.4%. Finally, a better fatigue performance of orthotropic steel deck is given.