Crack Growth Analysis Of Rib-to-deck Welded Joints Of Orthotropic Steel Deck Under Cyclic Loading With Negative Stress Ratio

Orthotropic steel bridge deck is a new kind of bridge structure that bears the vehicle loads by the integration of longitudinal ribs,transverse floor beams,steel deck and pavement.It has been widely used in long-span bridges,medium-span bridges and bascule bridges to substitute the traditional reinforced concrete bridge deck.However,as one of the most dangerous locations of the orthotropic steel deck,the rib-to-deck welded joint is subject to the negative stress ratio cyclic loading that the magnitude of compressive stress is much larger than the tensile stress.The fatigue damage accumulation is a very complicated process when the stress ratio R<0,and there is no analysis model available for its fatigue analysis at present.The fracture mechanics model based on Schwartz-Neuman alternating method is used in the fatigue analysis of the rib-to-deck welded joint of orthotropic steel bridge deck.To demonstrate the efficiency and accuracy of the Schwartz-Neuman alternating method,the stress intensity factors(SIF)of the two different surface cracks postulated at a regular pipe and a demisemi elliptical surface cracks at the nozzle-cylinder intersection of a typical reactor pressure vessel are investigated by using the SchwartzNeuman alternating method.The comparison with other analysis models and results reported in the literature shows that the Schwartz-Neuman alternating method can efficiently and accurately evaluate the SIFs of surface cracks of different shapes and depths with much smaller computational models,which indicates that the SchwartzNeuman alternating method is an efficient method in the evaluation of the SIFs of 3D cracks.A four-step approach is proposed to numerically analyze the fatigue crack growth of the surface cracks at the rib-to-deck welded joint of orthotropic steel deck that is under the action of cyclic loading with negative stress ratio.Firstly,the transverse stress at the rib-to-deck welded joint is computed based on the fatigue stress analysis model of orthotropic steel deck.Secondly,the SIFs along the surface crack tips at the rib-todeck welded joint are evaluated efficiently by using a 3D local model of the rib-to-deck welded joint and Schwartz-Neuman alternating method.Thirdly,the influence of the compressive stress in cyclic loading on the fatigue crack growth is studied by using a 2D fracture mode and a plastic damage model.The last step is to calculate the fatigue crack growth rate of the surface cracks at the rib-to-deck welded joint by substituting the stress intensity factors given in the second step into the fatigue crack growth formulas obtained from the third step.The present results of the fatigue crack growth rate demonstrate that the reverse plastic zone at the crack tip will accelerate the crack growth rate by more than 50% for the rib-to-deck welded joints of orthotropic steel deck under the cyclic loading with negative stress ratio.In this paper,the crack growth rate of the surface cracks at the rib-to-deck welded joint of orthotropic steel deck that is under the action of cyclic loading with negative stress ratio is studied for the first time.The results presented in this paper provide foundation for the fatigue life prediction of the rib-to-deck welded joints of orthotropic steel deck.