The Influence Of Pre-Splitting Crack’s Cracking Of Crts Ⅱ Slab Track On Bridge

CRTS Ⅱ slab track has been widely used to the high-speed railway system in China. Currently, CRTS Ⅱ slab track has been adopted for Beijing-Shanghai high-speed railway, Beijing-Tianjin inter-city high-speed railway and Shijiazhuang-Wuhan passenger dedicated line. CRTS Ⅱ slab track is the longitudinal continuously structure, which tends to crack under temperature load. So in order to control the random development of slab crack, the pre-splitting crack is set in the slab. If the pre-splitting crack cracks, the mechanical characteristics of the track structure will surely be affected. Also it will have an adverse influence on the normal behavior and durability of the track components. This research mainly includes the following aspects in terms of the cracking of the pre-splitting crack for CRTS Ⅱ slab.(1) Based on the field survey, the patterns of crack growth for different types of ballastless slab track has been summarized. In the case of CRTS Ⅱ slab track, the investigation results show that the crack occur not only at the pre-splitting crack, but also at the other parts of slab as well as at the joint of the new and old concrete for the wide seam.(2) The static model for the CRTS Ⅱ slab track on a bridge is established, based on the reasonable mechanical simplification. By means of the finite element method, the characteristics for pre-splitting crack cracking under different working conditions are analyzed. The research results show that the pre-splitting crack will not crack under positive temperature gradient or track load. However, when negative temperature gradient reaches50℃/m or temperature reduction extent reaches15℃, stress intensity factor KI will surpass the concrete fracture toughness, which means pre-splitting crack is very likely to crack at the moment. The seam between cement asphalt mortar layer and slab track will also affect the cracking behavior for the pre-splitting crack. Under the condition of the negative temperature gradient, the seam will restrain the cracking for the pre-splitting crack, while under the condition of temperature reduction, it will aggravate the cracking. Assuming that the pre-splitting crack has already thoroughly cracked in consideration of the consequent mortar layer damage (i.e. seam) around the crack, it will affect the cracking behavior for the adjacent pre-splitting crack. Namely, as long as one pre-splitting crack cracks, the adjacent pre-splitting cracks are hard to crack.(3) The mechanical behavior for the track components are analyzed after the pre-splitting crack cracked in terms of the pre-splitting crack in the track slab. The results show that after the pre-splitting crack cracking, the stress distribution for the slab track components, including slab, cement asphalt mortar, base plate and longitudinal-coupled reinforcement will change markedly. The cracking for the pre-splitting crack has a positive effect on the mechanical behavior of the slab, but it is disadvantageous for the cement asphalt mortar layer and the longitudinal-coupled reinforcement. Especially, the stress where the pre-splitting crack thoroughly cracked will have a sudden change. When the temperature reduction extent reaches10℃, the thorough cracking for the pre-splitting crack will induce the seam for the cement asphalt mortar layer. However when the positive temperature gradient reaches40℃/m or the negative temperature gradient reaches20℃/m, the cracking for the pre-splitting crack will not induce the seam for the cement asphalt mortar layer. When the positive temperature gradient reaches40℃/m or the negative temperature gradient reaches20℃/m, the cracking for the pre-splitting crack will not induce the consequent damage for the base plate. Also when the temperature reduction extent reaches10℃, with the adhesive damage between the cement asphalt mortar layer and the base plate taken into consideration, the cracking for the pre-splitting crack will not induce the consequent damage for the base plate either.