INFLUENCE OF INTERFACE BOND DAMAGE ON DYNAMIC CHARACTERISTIC OF CRTSⅢ SLAB TRACK

Zhiping ZENG，Jun LUO，Bin YAN，Wei WEI，Fushan LIU

School of Civil Engineering，Central South University，Changsha 410075

Abstract：The interface bond damage（IBD）between the slab and self-compaction concrete（SCC）is one of the most common damages of CRTSⅢ slab track.Based on the theory of vehicle-track coupling dynamics and the structural characteristics of CRTS Ⅲ slab track，a spatial vibration model for train-CRTSⅢ slab track interaction was established，and the influence law of IBD between the slab and SCC on the vibrations of CRTSⅢ slab track was revealed，by comparing the conditions without IBD and those with IBD.Research conclusions：（1）The results show that the dynamic responses of CRTSⅢ slab track generally increase with the rising of train speed and the depth of IBD，especially for the vertical tension of the faster，the dynamic responses of the slab，SCC，and foundation，as well as the interaction of the interface.Compared with conditions without IBD，the increase amplitude of the vertical tension of the faster may reach 5％ and 25％ respectively，the increase amplitude of the slab acceleration may reach 30％ and 70％，respectively，and the increase amplitude of the foundation acceleration may reach 35％ and 60％ respectively，when the depths of IBD are equal to 0.25 m and 0.50 m，respectively.（2）When the bond under the entire edge of the slab is damaged，the relative vertical acceleration between the slab and SCC may exceed 2 times the slab acceleration，and the patting between the slab，SCC，and foundation may increase greatly，which may lead to a faster damage of each part and the corresponding interface of CRTSⅢ slab track.（3）The depth and length of IBD should be strictly controlled during the maintenance of CRTSⅢ slab track.（4）The research results can provide useful references to the maintenance of CRTSⅢ slab track.

Keywords：CRTSⅢ slab track，interface bond damage，dynamic characteristic，train

Email：1964965318@qq.com

1　Introduction

CRTSⅢ slab track is a new type of ballastless track structure of China’s independent research and development，which has been successfully applied to Chenguan，Wuhan Intercity Rail，Cheng Mianle，Pan Ying，Shendan and other intercity，high speed railway，and is being constructed in Zheng-Xu，Jing-Shen High-speed Railway[1-4].Successful development and application of CRTSⅢ slab track attach great significance to expanding the influence of China’s high speed railway in the worldwide，improving international competitiveness，accelerating the implementation of the going-out strategies of the high speed railway and realizing the transformation from a large country to a powerful country of ballastless track.SCC is used as the packed layer below the track board，and U type connecting steel bars are arranged between the track board and SCC to form a composite board structure with tight connections.However，due to the different pouring time and elastic modulus，IBD may happen between the slab and SCC when acted by train loads，temperature loads and SCC shrinkage and other factors[5]，which has a impact on integrity and durability of the track structure and even affects the stability，comfort and safety of the operation of the high-speed trains in serious conditions[6].Reference[5]studied the stress characteristics of CRTSⅢ slab track under the condition of IBD from the static angle and put forward the maintenance level and assessment criteria for the interface bond damage.In this paper，the author mainly studies the vibration characteristics of CRTSⅢ slab track structure influenced by IBD between the track board and SCC under the train loads to provide references for the improvement of relevant maintenance codes.

2　Spatial Vibration Analysis Model for High Speed Train-CRTSⅢ Slab Track

2.1　High-speed train model

The high-speed train model is established by multi-body dynamics.Each section of 4 axes locomotive model is composed of 1 vehicle body，2 frames and 4 wheel-sets of total 7 rigid bodies with primary and secondary suspensions.The vehicle body and each frame contain 5 degrees of freedom including side-swinging，side-rolling，shaking，nodding and floating-sinking，each wheel-set contain 4 degrees of freedom including side-swinging，side-rolling，shaking and floating-sinking.Therefore，there exists total 31 degrees of freedom of each section of 4 axis vehicle.

2.2　CRTSⅢ slab track model

CRTSⅢ slab track model is established by finite element method.CRTSⅢ slab track mainly consists of rails，fasteners，slab，SCC，isolating layer，base board and other components.The rail is simulated by spatial beam elements；the slab，SCC and the base board are simulated by solid elements；the fastening system is simulated by linear spring-damper elements；the bond between the track board and SCC is simulated by uniform spring-damper elements.If the slab and SCC cohere well，large values of the stiffness and damping of spring-damper elements will be taken；if IBD occurs，the value of the stiffness and damping will be taken as zero within the region of IBD or nonlinear stiffness and damping will be applied according to the height of IBD[6].The isolating layer between SCC and the base board is simulated by vertical compressed spring-damper elements，the elastic cushion between spacing boss of SCC and groove of the base board is simulated by horizontal spring-damper elements and the foundation below the base board is simulated by uniform spring-damper elements.Dynamic analysis model of CRTS Ⅲ slab track can be obtained based on the above assumptions，which is shown in Figure 1.

2.3　Vibration equation of system and its solution

The spatial vibration equation of the system is established by taking high speed train-track structure as a big system，taking dynamic characteristics of each subsystem and interaction effects into consideration，taking interaction between wheel and rail as a bond[7]，taking irregularities of the track as an exciting source，using the principle of Darren Bell，the principle of potential energy in elastic system dynamics and the “set-in-right position” rule for forming structural matrices[8].The equation is solved by step-by-step integration method.

3　Calculation Conditions

Themarshaling modes of the high speed train are 1 dynamic adding 1 drag，and calculation length of the slab is 119 m，including 21standard track boards of 5.6 m.IBD is arranged in the bonding interface between the central slab and SCC.Due to the randomness of the concrete structure，the position of IBD may appear at any position of the bonding interface between the track board and SCC.The position of IBD can be roughly divided into 3 categories including edges of the slab，center of the slab and bottom of the rail according to the field investigation of the position of IBD.This paper conducted study on the influence of IBD occurred at the edge of the slab and the arranged conditions of IBD with its sense are shown in Figure 2.The slab is divided into 10×18elements（length and width of the each element are 0.25 m and 0.31 m），condition 1 means no IBD between the track board and SCC；condition 2 means the first element at the lower-left corner of the track board begins to separate from SCC and then extends gradually along the length and width in a clockwise direction.Supposing the train moves uniformly from the left to the right end of the track in the process of calculation.

4　Calculation Results and Analysis

This paper uses the aforementioned theory and calculation conditions，calculates the dynamic response of CRTSⅢ slab track when high speed trains pass by 250 km/h，300 km/h and 350 km/h and makes comparisons of the maximum variation range of the results between vertical dynamic response with IBD and without IBD.The calculated results were compared and analyzed，and the results can be found：

In general，the variation scope of each dynamic response index tends to increase with the increase of depth of IBD and train speed.

The degree of IBD influence on vertical tension of the fastener is greater than the vertical pressure of the fastener.There exists sudden change in IBD condition 53，the increase amplitude of the vertical pressure of the fastener is about 0.5％before the condition and is about 4％ after the condition and the increase amplitude of the vertical tension of the fastener is about 5％before the condition and is about 25％ after the condition；IBD may accelerate the damage of the fastening system.

The degree of influence of IBD on the vibration response of the slab is obviously greater than the base board.In general，there exists sudden change of the increase amplitude of the vertical displacement and acceleration（Figure 3 and Figure 4）of the slab，the increase amplitude is respectively about 10％ and 30％before the condition and the increase amplitude is respectivelyabout 50％ and 70％ after the condition.

The maximum value of the vertical relative displacement，velocity and acceleration between the slab and SCC may change suddenly when the end or edge of the slab is completely separated from SCC（Figure 5 and Figure 6）.In general，the vertical downward relative acceleration between the slab and SCC is basically equivalent to the slab before IBD condition 53，however，the vertical downward relative acceleration between the slab and SCC is more than two times as much as the slab，which illustrates that there exists a reverse shock vibration between the slab and SCC，which increases the impact action between the slab and SCC and accelerates the damage rate of both.

The degree of IBD influence on the displacement of the base board is less than the slab，but the influence of acceleration on base board is basically equivalent to the slab.Before IBD condition 53，the increase amplitude of the displacement and acceleration of the base board is about 1％ and 35％ and about 6％ and 60％after the condition.

The maximum value of the vertical relative displacement，velocity and acceleration between the base board and SCC may change suddenly when the end or edge of the slab is completely separated from SCC.In the case of the train speed 350 km/h，before and after the IBD condition 28 and 53，the increase amplitude ofthe vertical downward relative velocity is respectively 20％，80％ and 100％ increase amplitude ofthe vertical downward relative acceleration is respectively 15％，50％ and 85％.Complete separation of the end or edge of the slab may obviously increase the impact action between the base board and SCC and accelerate the damage rate of the isolating layer.

5　Conclusions

（1）In general，the results show that the dynamic responses of CRTS Ⅲ slab track generally increase with the rising of train speed and the depth of IBD；IBD has little influence on the wheel-rail vertical force，vertical displacement of the rail，and vertical pressure of the fastener and vertical displacement of the base board but has obvious influence on vertical tension of the fastener，the acceleration of track board，SCC and base board as well as the inter-facial interaction.

（2）The increase amplitude of the vertical displacement and acceleration of the track board and base board may change suddenly when the end or edge of the slab is covered with IBD.

The increase amplitude of the slab vertical displacement may increase from 10％ to 50％and acceleration may increase from 30％ to 70％，the increase amplitude of base board vertical displacement may increase from 1％ to 6％ and acceleration may increase from 35％ to 60％.

（3）There may exist reverse shock vibration between the slab and SCC，which increases the rattling effect on IBD between the slab and SCC and accelerates the damage rate of both.

（4）Complete separation of the end or edge of the slab may result in exponential increase of the relative vertical displacement，velocity and acceleration，which accelerates the damage of the isolating layer.

Acknowledgement

The research described in this paper was financially supported by the Project of Innovation-driven Plan in Central South University（No.2015CXS014）；the Joint Fund of the National Natural Science Foundation of China（No.U1334203，No.U1361204，and No.U1434204）.

References

[1]He Y.P.，2011.Study on Fatigue Property of the CRTSⅢ Slab Track[D].Chengdu：Southwest Jiaotong University.

[2]Wang C.X.，2011.Study on Mechanical Characteristic of CRTSⅢ Type Slab Ballastless Track[D].Beijing：Beijing Jiaotong University.

[3]Wei H.D.，2013.Research on the Structure Design of New Unit Slab Ballastless Track on the Zhengzhou-Xuzhou Railway Passenger Dedicated Line[D].Changsha：Central South University.

[4]Sun L.，Duan Y.F.，Yang X.，2013.Static Response Analysis of CRTS Ⅲ Ballastless Track Structure[J].Journal of Railway Engineering Society，11：32-39.

[5]Yang Z.，2014.Mechanics and Maintenance Standards of Connection Damage for CRTSⅢ Slab Track[D].Chengdu：Southwest Jiaotong University.

[6]Li P.G.，Liu X.Y.，Li G.Q.，2014.Influence of CA Mortar Void on Dynamic Characteristics of Unit Slab Track on Bridge[J].China Railway Science，35（3）：20-27.

[7]Zhai W.M.，2015.Vehicle-track Coupled Dynamics（Fourth Edition）[M].Beijing：Science Press.

[8]Zeng Q.Y.，Guo X.R.，1999.Theory of Analysis of Vibration of Train-Bridge Time-variant System and its Application[M].Beijing：China Railway Publishing House.

ICRE2016-International Conference on Railway Engineering