Study On Crack Initiation And Propagation In The Anchorage Structure Of CRTSⅡ Slab Ballastless Track

As an important part of CRTSⅡ slab ballastless track,anchorage structure is set in the transition section of road and bridge.In the course of service,the anchorage structure mainly plays the role of anchoring the temperature force of the base slab and bearing the train load.As the main part of the anchorage structure is concrete,the existing research shows that the possibility of the anchorage structure cracking under external load is very large,and the crack will seriously affect the durability of the concrete structure.Therefore,based on damage mechanics,fracture mechanics theory,this paper studies the crack initiation and propagation law of CRTSⅡ slab ballastless track under the conditions of temperature force and uneven settlement of subgrade through finite element simulation.(1)The mechanism of temperature force is studied.The results show that the temperature force of the base slab borne by the anchorage structure is directly proportional to the elastic modulus of the base slab.The cracking phenomenon of the base slab in actual operation will lead to the reduction of the elastic modulus of the base slab within a certain range.The cracking state of the base slab has a great influence on the temperature force acting on the anchorage structure.(2)Based on damage mechanics theory,the finite element model with plastic damage factor of concrete is established to analyze the location,opportunity and trend of the crack initiation under the conditions of temperature force and uneven settlement of subgrade.The results show that when the base slab is in the uncracked state,it is the most unfavorable condition for the anchorage structure crack initiation under the action of temperature force.With the continuous cracking of the base slab,under the action of the temperature force of the base slab when the temperature is reduced to 60 °C,the possibility of crack initiation at the connection between the main anchorage structure vertical wall and the main anchorage structure bottom plate is the largest,and under the action of the temperature force of the base slab when the temperature is increased to 40 °C,the possibility of crack initiation at the connection between the main anchorage structure vertical wall and the friction plate is the largest.With the increase of uneven settlement amplitude of subgrade,the position of friction plate at the beginning of settlement is the most prone to crack initiation,followed by crack initiation at the middle and end of settlement.(3)Using the theory of linear elastic fracture mechanics of concrete to establish a finite element model of anchorage structure with preset cracks.The equivalent stress intensity factor and crack angle at the crack tip of the rigid connection between the main anchorage structure vertical wall and the friction plate,the main anchorage structure bottom plate under different working conditions are obtained,and then the crack propagation law at the rigid connection between the main anchorage structure vertical wall and the friction plate,and the main anchorage structure bottom plate is analyzed The results show that compared with the crack length,the crack depth has a greater influence on the crack growth at the joint of the main anchorage structure vertical wall,the friction plate and the main anchorage structure bottom plate,and with the increase of the crack depth,the temperature force and the uneven settlement of the subgrade will cause the crack growth at the two places.The joint between the main anchorage structure vertical wall and the friction plate is the place where the anchorage structure is most prone to crack growth,and the most unfavorable condition for the anchorage structure crack growth is that the base slab is not cracked when the temperature rises to 40 °C.