Experimental design of the flexural stiffness attenuation of track slabs under fatigue load
[Objective]A ballastless track slab in service is repeatedly subjected to multiple cyclic loads,thereby becoming prone to issues such as decreased structural load-bearing capacity and fatigue failure under such conditions.These problems can seriously endanger the safety of train operations.Therefore,the remaining load-bearing capacity of track panels must be quantitatively characterized under service conditions.[Methods]Based on the theory of concrete plastic damage,experiments and analyses were conducted to assess the actual damage to track slabs.Using the temperature field of the track slab and the monitoring data of the wheel-rail force,a load spectrum was fitted to design a fatigue test under the coupling effect of temperature and dynamic load.A rigid cushion block with reasonable stiffness was arranged at the lower end of a prefabricated steel beam according to load requirements,which was used to ensure that the vertical load of the testing machine could be evenly distributed to the point of action of the track slab.Four-point bending and tensile tests were conducted on the track slab to obtain residual deformation and mid-span deflection at different stages.The evolution characteristics of plastic damage and bending bearing capacity under fatigue loads were quantified.[Results]The study found that multifield coupled fatigue effects cause plastic damage to the ballastless track slab,leading to continuous deterioration in its bending bearing capacity.After unloading,the mid-span of the track slab could not return to its original position,indicating some residual deformation.As the number of coupled load cycles increased,both the residual deformation and mid-span deflection of the track slab showed an upward trend.This indicates that internal damage within the track slab is gradually intensifying,leading to a decrease in overall bending resistance.After coupling with cyclic loads,the residual deformation of the track slab at mid-span increased from 0.048 mm to 0.051 mm,marking a 6.25% increase compared to the initial residual deformation.The mid-span deflection of the track plate increased from 1.645 mm to 1.766 mm,which is a 7.36% increase compared to the initial displacement.These changes indicate a 6.85% decrease in the overall bending bearing capacity of the track slab.[Conclusions]The residual plastic deformation of the track slab serves as a macroscopic characterization of internal damage.The gradual increase in plastic deformation with the number of load cycles indicates a deterioration in the actual load-bearing performance of the track slab.The increasing mid-span deflection further confirms the degradation of the actual bending bearing capacity.The overall performance deterioration of the track slab under service conditions would inevitably lead to changes in structural stress and deformation characteristics.In actual maintenance and repair,special attention should be paid to the actual state of weak positions in the ballastless track slab,and reasonable reinforcement measures should be adopted.
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