Numerical analysis on fatigue behavior of ultrahigh-performance concrete-Orthotropic steel composite bridge deck

Ultrahigh-performance concrete-orthotropic steel composite bridge deck is composed of the orthotropic steel deck and a thin ultrahigh-performance concrete (UHPC) overlayer. In the previous fatigue tests, two typical fatigue failure modes were found and identified. As a supplementary test after fatigue tests, air penetration method is capable of providing a reference to the quantitative and non-destructive damage detection of fatigue damage of UHPC. To further the previous study, a detailed numerical investigation is accomplished through complimentary finite element (FE) analysis. Compared with the solid element model, the refined shell-solid element model can better reflect the mechanical behavior. It is illustrated that the vertical stress can be adopted in assessing the fatigue strength of rib-to-diaphragm welded connection in the field test by means of nominal stress method. The combination of various factors would lead to fatigue shear failure of the short headed-studs. The fatigue strength of rib-to-diaphragm welded connection predicted by the hot spot stress method and the consistent nominal stress (CNS) method can basically meet the requirements of FAT90. The consistent nominal stress method can be used as the optimization method of nominal stress of fatigue detail. It is demonstrated that the fatigue life of UHPC can be estimated by S-N curves of ordinary concrete conservatively. The allowable equivalent maximum stress level can be taken as 0.55 for two million cycles of fatigue loading, and 0.52 for five million cycles of fatigue loading.

Analysis on Stop-hole Parameters for Fatigue Cracks at Arc Notch in Steel Bridge Deck

Two types of fatigue cracks at arc notch in steel bridge deck were repaired by drilling stop-holes. The effect of stop-holes with different diameters and positions was considered. Based on finite element models, the variation laws of stress distribution and the effects of stress concentration were compared for different stop-hole diameters and positions. Analysis results indicated that stop-hole can effectively improve the stress concentration at crack tip and the fatigue life of components can be considerably increased. The crack-stopping performance enhances with the increase of stop-hole diameter, but large stop-hole cannot effectively retard crack growth. The stop-hole performs well with the location at -0.5D∼0.5D. The maximum stress point still appears at crack tip when the stop-hole is outside or inside the crack. The stop-hole diameter has no effect on the stop-hole location.