Study On Vibration Reduction Performance Of Viscoelastic Damping Track Bed In Checkerboard Interface

The viscoelastic damping track bed was a new type of track bed damping method inspired by the constrained damping structure.The main body of the structure was composed of a track bed(constrained layer),a base layer and a damping layer composed of viscoelastic damping materials.However,in actual engineering,the track bed was impacted by train due to emergency braking,so that the shearing force of the track bed on the damping layer was too large.Causing the damping layer to tear and the relative slip between the track bed and the base layer to avoid such phenomena.It was particularly important to increase the lateral stiffness of the viscoelastic damping track bed.The checkerboard interface between the track bed and the damping layer,the damping layer and the track bed was arranged to engage each other,which not only increases the laying area of the damping layer,but also increases the section rigidity,Using the mechanical bite force between the base layer and the constraining layer to suppress the relative slip between the constraining layer and the base layer caused by vehicle braking,making it suitable for tougher working conditions.In this paper,the damping properties of a modified polyurea viscoelastic damping material Qtech-413(Qtech-413 for short)were studied,which provides material properties for the simulation of large tunnel structures.Then the soil-tunnel-track bed structure model was established by ANSYS,and the damping characteristics of the viscoelastic damping track bed were preliminarily understood.Finally,the viscoelastic damping track bed model of the checkerboard interface was designed and fabricated.The single-point hammering experiment was carried out by using simply supported beam and elastic support methods.The damping performance of the viscoelastic damping track bed was further studied.The dynamic mechanical properties of the viscoelastic damping material Qtect-413were studied by DMA.The parameters vary with temperature in the whole temperature range.The storage modulus decreased with the temperature,and variation trend of the loss modulus was opposite.The loss modulus increases first and then decreases with temperature,and the peak value was obtained at the glass transition temperature T_g;The variation trend of loss modulus with frequency was the same as that of energy storage modulus,and increased with frequency at a fixed temperature.For the simulation of the viscoelastic damping track bed in the tunnel structure,the vibration response of the integral track bed and the viscoelastic damper bed in the tunnel structure was obtained.The results show that the tunnel inside the same damping layer was used when the load frequency was increased from 5 Hz to 25 Hz.The time curve peak value of 0.72m/s~2 transitions to 1.2m/s~2;When the load frequency was 25 Hz,the effective value of vibration acceleration decreases by 7.9%,14.8%,and 22.1%,respectively,as the thickness of the damping layer of the track bed increases.In the study of the attenuation of surface vibration response,the vibration damping effect of the viscoelastic damper bed was stable in the range of 0~5m from the center of the tunnel.From the center of the surface tunnel 5~25m,the surface vibration acceleration decreases significantly,which was about 75%.And as the thickness of the damping layer increased,the faster the decreaed;From the center of the surface tunnel 25~50m,when the load frequency was 5~10Hz,the vibration response of the surface appears magnified by the influence of elastic wave,and the 5mm damping layer of the viscoelastic damper bed has a good inhibitory effect on the vibration amplification area,and the vibration frequency of the load frequency was 15~25Hz,and the vibration acceleration was still monotonously decreasing.,and tends to be gentle after 60m.The vibration experiment of the damping structure model of the checkerboard interface under the constraint of simply supported beam shows that with the increase of the thickness of the damping layer,the vibration durations of the selected three models were 0.01807s,0.02832s,0.02295s.The vibration holding time was relatively stabilized at about 30%,and the vibration acceleration amplitude was reduced by 15%and 24.6%;In addition,compared with the integrated track bed model,the viscoelastic damper bed model has a vibration acceleration level of 14.4dB,15.4 dB,and 20.2 dB,,and the damping effect was significant;Under the condition of elastic support,with the increase of the thickness of the damping layer,the total effective values of the vibration acceleration of the selected three models were 2.56 m/s~2,1.77 m/s~2,1.52 m/s~2,and the maximum reduction was 68.4%.Through time domain analysis,1/3 octave spectrum and model composite loss factor analysis,it can be seen that increasing the thickness of the damping layer and the track bed(constraint layer)can greatly reduce the vibration acceleration level of the viscoelastic damping track bed at the checkerboard interface and the acceleration amplitude of the vibration time domain.Effectively shortening the vibration duration of the model,which was very helpful for the improvement of the damping performance of the model.The same model was subjected to single-point hammering experiments under simply supported beams and elastic supports.By comparison,the total acceleration values of the model were 106.8dB and 116.91dB,and the difference was obviously about10dB.The model composite loss factor was under the two support conditions,it was0.1960 and 0.1245.It can be seen that the simple beam support improves the model constraint and reduces the degree of freedom,which improves the stability of the model.The research results show that the thickness of the damping layer and the track bed(constraint layer)was improved when the design of the viscoelastic damping track bed on the checkerboard interface is made,so that the model has better damping performance.In addition,the base layer and the track bed(constrained layer)were arranged to be engaged with each other,on the one hand,the relative slippage of the base layer and the track bed(constraint layer)due to excessive lateral load can be avoided,on the other hand the setting of the special-shaped interface is equivalent to the area of the damping layer was increased to better control the train vibration.