Research On Law Analysis Of Pre-splitting Cracks Cracking Of CRTS? Slab Ballastless Track

With the development situation of high-speed railway in our country,it is hard to avoid damage for CRTS-II slab ballastless track under the cycle action of temperature load for a long time.In the the damage,track slab crack fracture is considered common damage type.For the damage phenomenon that none-pre-splitting fracture is more frequent and ruleless than pre-splitting fracture on track slab,it is necessary to study pre-splitting fracture,and analyze the cracking law and its influence on track structure,providing theoretical guidance for fracture damage repair of CRTS-II slab ballastless track.This paper,based on the summary of research status at home and abroad about ballastless track crack damage,adopts cohesive zone model theory(CZM)to analyze pre-splitting crack of model of CRTS-II slab ballastless track.Establish simplified plane model of CRTS-II slab ballastless track,calculate and analyze pre-splitting crack characteristic of CRTS-II slab ballastless track,and conclude pre-splitting cracking laws and their effects.Calculation results show that,under various conditions,because the wide-narrow juncture interface is the most weak position longitudinally,after the steel bar tensioning,the interface,under the temperature drop effect,will crack first,causing corresponding interlayer damage,which leads to certain debonding on both ends of slab.Then with the point damage expanding gradually downward,due to the abate constraints between the layers,the 1st and 9th pre-splitting cracks on both ends of slab split first.The rest will present the symmetrical cracking rule in turn from middle to both ends every four or two sleeper width.Under the whole temperature drop action,the interlayer damage of the CRTSII slab ballastless track is mainly in the form of shear failure.Under the effect of negative temperature gradient,the interlayer damage is mainly in the form of tensile failure.When the negative temperature gradient is combined with the overall temperature drop,the interlayer damage is mainly presented in the mixed form of tensile and shear failure.After pre-splitting cracks cracking,significant mutations will happen to the longitudinal stress of track slab and reinforcement in the cracking position,reinforcement stress will generally not exceed the yield strength;stress value mutation of track slab is not real stress,only as a recognition base of pre-splitting cracks cracking.Its real stress is the contact stress in the cohesive zone model.For the cracks that already has split,its stress has been zero.When the temperature effect is larger,the track slab stress exceeds concrete tensile strength value.In addition to the reason of software calculation that the linear elastic element simulating track slab makes its stress increase persistently,in the actual process,the track slab may appear none-pre-splitting fracture,resulting in more track structure damage and stress overrun.In addition,the track slab stress in the process of before and after pre-splitting cracks cracking is reduced by overall release,particularly the reduce range gets to the sharpest within two-sleeper width on both sides of the cracking position.Finally when the crack spacing is uniform of two-sleeper width,track slab stress tends to be evenly distributed.In the situation of overall temperature drop,the track slab longitudinal displacement increases gradually with continuous cooling.Because of large interlayer damage on the both ends,longitudinal displacement decreases gradually from both ends to the middle;In the situation of negative temperature gradient,the track slab presents distinct warping displacement in the cracking position,and reached the maximum on the both ends.Under various conditions,the maximal displacement of track slab on the both ends exceeds allowed value,which should be paid more attentions on.