Field study using additional rails and an approach slab as a transition zone from slab track to the ballasted track
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Abstract:
An abrupt change in the stiffness of railway tracks at the junction between slab track and ballasted track causes increased dynamic loads, asymmetric settlements, damage of track components, and, consequently, increased maintenance costs. Due to this, a transition zone is usually built at the junction between the ballasted and the ballastless tracks to reduce the aforementioned problems. One of the methods suggested as a transition zone in these areas is to use a combination of an approach slab and additional rails. This study evaluates the dynamic behavior of this type of transition zone using field tests and also compares its performance with a transition zone built only with an approach slab. Hence, in the Tehran–Karaj railway line, two types of transition zones were constructed: one including only the approach slab and the other one including additional rails and an approach slab. Then, by conducting some field tests, the dynamic behavior of the track in these two types of transition zones was examined. The results of the field measurements show that for the analyzed case study, at the combined transition zone with additional rails and an approach slab, instead of a sudden increase in rail displacements from the slab track to the ballasted track (i.e. by 53%), initially, in the first part of the transition zone (with additional rails and an approach slab), the deflections increase by an average of 31%, and then in the second part of the transition zone (with additional rails only) the deflections increase additionally by 11%.Keywords:
Slab
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Ballast
Substructure
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In this paper, in order to do research on the characteristics of reducing vibration and declining noise of concrete floating slab track, the vertical dynamic analysis model of vehiclefloating slab track is established with the use of finite element analyses method. By using this model, dynamic responses of floating slab track are studied under different conditions of train’s speed, stiffness and damping of infrastructure, structure size, etc. On the basis of this research, some suggestions for design of floating slab track are put forward.
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The lateral finite strip and slab segment element is used to simulate the slab track with the structure features of the slab track considered.Based on the principle of total potential energy with stationary value in elastic system dynamics and the rule of set-in-right-position for formulating system matrixes,the vertical vibration equation set of the high-speed train and slab track time-dependent system are established with the vertical connecting condition between the wheel and the rail considered.The effect of the stiffness change of the slab track on the vertical dynamic characteristics of the system is analyzed.The calculated results demonstrate that the reasonable stiffness of the slab track can effectively reduce the vertical vibration response of the system.The proposed stiffness value ranges of CA mortar and rail pad are 1000—1500 MPa/m and 60—80 kN/mm respectively.
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The history of slab track construction in Germany is described. A total of 155 km of double-track slab track has been constructed on the Cologne-Rhine/Main 300 km/hour high-speed line. The design parameters that led to slab track being chosen over ballast track for the high-speed line are outlined. Construction of the slab track on the new line is discussed with reference to the rail supports, concrete-embedded two-block sleepers, the Rheda and Zueblin systems, turnouts, bridges and expansion joints. The other slab track systems used in the high-speed network of DB Netz AG are outlined.
Slab
Ballast
Railway line
Line (geometry)
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Deteriorated track-slabs have been so far found in some areas subject to cold weather conditions. For track-slab maintenance purposes, it is very important to understand the causes of this deterioration. Visual inspections of track-slabs and investigation of samples of materials used in track-slabs were therefore carried out. Visual inspections found that deterioration occurred more frequently on south facing sides of track-slabs exposed longest to the sun. Material investigations showed that track-slab deterioration was caused by an alkali-silica reaction and frost damage.
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Frost (temperature)
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Research purposes: The basic component of the track structure with isolated rubber floating slab is the concrete slab track born by the elastic element.The research was done on the mechanical properties of the floating slab,the analysis was made for the natural frequencies,mechanical response under dynamic load and damping performance,and the discussion was made on the reasonable thickness of the ballastless track to provide the reference to the track design. Research conclusions:The research results show that the natural frequency of the track system decreases with the increase of the thickness of the ballastless track,and the rate of change decreases with increase of the track thickness.The acceleration insertion loss of the track basis increases with the increase of the thickness of the ballastless track,and the rate of change decreases with increase of the track thickness.When the thickness of the ballastless track reaches at 0.4m,the corresponding dynamic performance,the damping performance effect and the concrete amount of track bed are rather economical.From the present theoretical analysis and online testing,it can be seen the damping performance effect of the isolated rubber floating slab system is obvious,and its construction and maintenance programs are systematic.
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Natural frequency
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Effective beam width model (EBWM) has been widely used for predicting lateral drifts and slab moments in flat slab structures under lateral loads. As the slab moment due to lateral loads increases, slab stiffness decreases due to crack formation. The accuracy of the EBWM strongly depends on how the reduced slab stiffness is estimated. For this purpose, this study developed equations for calculating slab stiffness reduction factor (β) by conducting nonlinear regression analysis using stiffness reduction factors estimated from collected test results. The slab stiffness reduction factor (β) is defined as a ratio of reduced slab stiffness due to crack formation to the stiffness of the uncracked slab section. For verifying the proposed equation, the lateral stiffness of two slab–column connection specimens tested by the writers was compared with the lateral stiffness calculated using the EBWM with the proposed stiffness reduction factor. Further, two flat plate specimens having two continuous spans were also considered for verifying the proposed equations for β.
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Both ballasted track and slab track are commonly used in high-speed railways. Based on the theory of vehicle-track coupled dynamics, the wheel-rail dynamic responses in the rail weld zones of these two tracks are investigated, and the P 1 , transient high-frequency impact force, and the P 2 , low-frequency impact force are analysed. The results show that, due to the high stiffness and small damping ratio of the vehicle and the ballasted track system, the P 1 force of the ballasted track is generally greater than that of slab track while the P 2 force is smaller than slab track. Furthermore, the duration of the impact load of ballasted track is longer than that of slab track. The results will provide a reference for the analysis and evaluation of ballasted tracks in high-speed railways.
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Reactive Powder Concrete is proposed to be used in the ballastless track for its excellent material properties due to existing problems of high speed railway ballastless track. Three different unit types of RPC frame slab track were proposed through optimization design and the mechanical behavior of these frame slab track was analyzed. The results show that the RPC slab track meet the requirements of bearing capacity, the suggested type of RPC slab track is a frame slab with increased thickness because of its higher techno-economic advantages.
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