Analysis Of The Shear Strength And Fatigue Life Of Stud In Steel-UHPC Composite Bridge Deck

Steel-UHPC composite bridge deck is a new type of bridge deck pavement for orthotropic steel bridge deck,which can effectively reduce the pavement damages and fatigue cracks in orthotropic steel bridge deck.The stud connector bears the shear stress between the deck plate and UHPC layer,and it is the key component that affect the bending stiffness of the composite bridge deck.The thesis evaluates the stud shear strength of steel-UHPC composite bridge deck by a submodel for the computation of the interlaminar shear stresses and studies the shear fatigue performance of stud based on an efficient fracture mechanics model.The major topics in the thesis are as follows.(1)The submodel for computing interlaminar shear stresses of steel-UHPC composite bridge deck is established.Based on the Haihe Bridge,Tianjin,the finite element model of steel box girder segment,the simplified model and the submodel are established to compute the interlaminar shear stresses of composite bridge deck.Through the comparison of the computation results of interlaminar shear stresses,it is shown that the submodel can be used as an accurate and efficient finite element model to compute the interlaminar shear stresses of steel-UHPC composite bridge deck.(2)The shear strength evaluation of the stud in steel-UHPC composite bridge deck is carried out.Based on the submodel,the most dangerous transverse wheel position on the composite bridge deck is determined.The maximum interlaminar shear stresses of the steel-UHPC composite bridge deck under the wheel load always occur at the deckUHPC layer interface above the floor beam.The shear strength of the stud in steelUHPC composite bridge deck is evaluated according to the four formulas for shear resistance of stud in conventional steel-concrete composite structures.The comparison with test results shows that this method has great limitations in evaluating the shear strength of the short stud in steel-UHPC composite bridge deck.The method of filling the diaphragms inside the U-ribs on the floor beam plane can effectively improve the stress state of the deck-UHPC layer interface,and reduce the interlaminar shear stress of the composite bridge deck by more than 50%.(3)Analysis of three-dimensional(3D)fracture mechanics of stud welded joint crack is conducted.A 3D fracture mechanics model of the stud welded joint is established based on the Schwartz-Neuman alternating method,The computation results show that the crack at the root weld toe of the stud is more likely to cause the fatigue damage than the crack on the upper weld toe,and the penetration weld stud has higher fatigue strength than the girth weld stud.The crack of stud welded joint under the interlaminar shear force between the deck plate and UHPC layer belongs to mixed mode crack(Ⅰ+Ⅱ+Ⅲ).The initial crack size,initial crack angle and stud welding area have great influence on the SIFs of stud welded joint crack.(4)The fatigue life of studs in steel-UHPC composite bridge deck is predicted based on welded joint crack propagation.The stud welded joint crack exhibits nonplanar propagation during the propagation process,and the crack gradually changes from the mixed mode crack to mode I crack.The predicted values of the fatigue life of the studs based on Schwartz-Neuman alternating method are in good agreement with the measured values in the push-out tests.The established submodel provides an accurate and efficient finite element model for the stress analysis of large bridge structures.The fracture mechanics model used provides a reliable and efficient numerical method for fatigue evaluation of steel bridge welded joint.