Study On Fatigue Deterioration Mechanism And Performance Strengthening Of Rib-to-deck Welded Joints Of Orthotropic Steel Bridge Deck

Fatigue cracking of rib-to-deck welded joints of orthotropic steel bridge deck(OSD)is prominent under the wheel load.Reinforcement of fatigue cracking area is required.It is of great importance to accurately evaluate the fatigue performance of rib-to-deck welded joints after reinforcing.Rib-to-deck welded joints have multi-fatigue cracking modes.Stress changes of cracking area or the stress intensity factors(SIFs)reduction at the crack tip cannot reflect the characteristics of rib-to-deck welded joints.On the basis of the preliminary study of the crack arresting performance of each reinforcement method,the studies of the fatigue deterioration mechanism before reinforcing and strengthening performance after reinforcing are completed.The dominant fatigue failure mode is confirmed and the residual fatigue life is calculated.Thus,the reinforcement methods are evaluated by the fatigue properties of rib-todeck welded joints.The main research contents and conclusions are as follows:(1)Based on linear elastic fracture mechanics and equivalent structural stress method,a reinforcement evaluation frame for rib-to-deck welded joints is proposed.The fatigue modes which are prone to fatigue cracking are comprehensively considered in this evaluation frame.The determination method of dominant fatigue failure mode and the calculation flow of residual fatigue life provide a new idea for fatigue reinforcement research.(2)Based on the finite element software ANSYS,the crack propagation process of three typical fatigue failure modes of rib-to-deck welded joints are simulated.In the crack propagation process from the initial defect to the critical crack size,the variation of SIF amplitude with crack propagation depth at the crack tip is studied.Calculation results show that the crack propagation of three studied fatigue cracks is all dominated by Type-I cracking.The crack slenderness ratio increases with the increase of crack propagation depth,and its shape tends to flatten.(3)The retard effectiveness of various reinforcement methods on the fatigue crack of ribto-deck welded joints is studied.Linear elastic fracture mechanics are adopted.For surface unbroken crack which initiate from weld root and propagate along the deck,the crack-arrest effectiveness of both the internal welding and UHPC pavement are excellent.For surface unbroken crack which initiate from weld toe and propagate along the deck,crack-arrest effectiveness of introducing angle steel,U steel nor I-beam is unsatisfied.The effect of introducing UHPC pavement is excellent.For surface broken crack which initiate from weld root and propagate along the weld,the introduction of internal welding,assembly reinforcement and UHPC pavement cannot obtain satisfied crack-arrest effectiveness.It is mainly because of the unusual stress mode at the weld throat.Based on the equivalent structural stress method,the effects of the introduction of each reinforcement method on the stress response of the non-cracking mode is calculated.It is proved that the introduction of reinforcing methods may change the mechanical behavior characteristics of the original structural system and adversely affect the non-cracking mode.(4)Based on the established reinforcement evaluation frame,the studies of the fatigue deterioration mechanism before reinforcing and strengthening performance after reinforcing are completed.The dominant fatigue failure mode is determined and the residual fatigue life is calculated.The fatigue performance strengthening effects of different reinforcing methods are compared.