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Meta-structured concrete fabrication and radiated sound analysis of rolling noise for complex polymer concrete slab railway

Meta-structured concrete fabrication and radiated sound analysis of rolling noise for complex polymer concrete slab railway
Other Titles
메타 구조 콘크리트 제작 및 복합 폴리머 콘크리트 슬라브 궤도의 구름 소음 해석
Sangkeun Ahn
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Train system is essential transportation due to its high speed and large scale comparing with vehicle. Although train system has many benefit as above, radiated sound from train make annoyance to residents near railroad. The train noise mainly consists of aerodynamic noise, driving noise from power sources, rolling noise from wheel, rail track and sleepers. When train running faster than 300 km/h, the aerodynamic noise becomes dominant component of the train noise. However, rolling noise contributes train noise over all speed range. To reduce rolling noise, the web damper installed on the track and the high damping pad under the track have been investigated. The web damper covers only low frequency range and rail pad causes high maintenance cost. Cement concrete sleeper of high speed railway is major component of the rail system. Due to flexural deflection of train and rail track, elastic characteristics of concrete sleeper affects vibration of rail system. High damping concrete sleepers are needed to solve the noise problem induced from rolling noise. Radiation characteristics of rolling noise was predicted by applying moving load theorem. Running train on rail track is modeled as moving load on infinite beam. Relationship between the loss factor of supporting stiffness and the rail vibration was analyzed. Radiated sound power and directivity of rolling noise from rail vibration were identified with different the load velocity. Concrete cement has been widely used as a material in civil engineering structures due to its flexibility and load holding capabilities. However, Portland cement concretes have exhibited problems arising from excessive noise and vibration generation due to their low damping. In this paper, polymer concretes made with an epoxy resin were studied and their ability to reduce noise/vibration in a concrete slab track was examined. The polymer concretes were fabricated with different mixing ratios of the epoxy resin/aggregate and aggregates of different sizes. The effects of these variables on the compressive and flexural strengths of the polymer concretes were measured to study the mechanical reliability under water absorption environments. Also, the frequency dependent variations of stiffness and damping in the polymer concretes were obtained by impact vibration tests to study their ability to reduce vibrations. The fatigue tests of the concretes were performed by applying periodic load for bending tests. To investigate the reduction of stiffness due to fatigue damage, the frequency dependent variations of the dynamic stiffness and the loss factor of the polymer concretes (a mixture of epoxy resin, carbon fiber and aggregates) were obtained by impact tests. The variation of the dynamic properties before and after the fatigue tests was measured. The separated beam method was used to identify the stiffness distribution along the concrete specimen. This method analyzed the beam vibration using evenly spaced beam elements. The boundary conditions of displacement and slope continuity at end of each element were imposed. The least square method was applied to estimate the dynamic properties of the beam elements from the measured vibration response. This procedure was required to identify small change in the dynamic properties induced during fatigue tests. Consequently, the durability of the carbon fiber reinforced polymer concretes was validated by comparison with normal polymer concretes. A pipe structure was embedded in polymer concrete specimens. The frequency-dependent variations of the dynamic stiffness and the loss factors of the specimens were measured by the vibration test method so that the damping enhancement from the embedded structure could be identified. The weight reduction effect of epoxy resin usage was compared after pipe embedment. Impact dampers were applied to the pipe-embedded polymer concretes to improve their vibrational energy dissipation. The impact dampers were fabricated through the insertion of impact balls into the pipe structures. The dynamic properties of the impact-damper-positioned polymer concretes were obtained by vibration tests. The damping performance was investigated according to the gap size between the impact ball and the pipe. An analytic model was used to predict the vibrational behavior of the polymer concrete when the impact dampers were applied. Consequently, the effect on vibration damping was identified for different mass ratios and gaps to find optimal construction. As another way to improve damping performance of the concrete sleeper, complex concrete which is polymer concrete was inserted in cement concrete was fabricated. The adhesion force at the interface between the polymer concrete and the cement concrete was investigated from impact test. A cylindrical embedment structure was fabricated by using a silicon mold and the embedment was placed in direction of length and height. From the cylindrical embedment, more suitable embedment shape was determined by measuring the flexural strength and the loss factor. A wave type embedment structure was designed in order to improve the performance of the complex concrete. With the longitudinal direction, the height of the polymer concrete change continuously. The responses of the complex concretes were also measured using accelerometers by impact excitation. The characteristics of the metamaterial was identified from the periodic nonlinear interface. An analysis model considering the classical laminate theorem to investigate the damping effect of wave type embedment was imposed. To verify the damping performance of meta-structured concrete, actual size meta-structured concrete sleeper was fabricated. The averaged loss factor of the complex sleeper in frequency range from 50 Hz to 3.2 kHz was compared with that of the cement concrete sleeper. It was found that the meta structure using the polymer concrete wave pattern is also effective in improving damping performance of an actual concrete sleeper. Lastly, the dynamic properties of the measured complex concrete were applied to the rolling noise analysis model. The rolling noise form railway in velocity of 300 km/h was analyzed. Using meta-structured concrete sleeper, the radiation of the rolling noise was reduced effectively. This investigation on the characteristics of concrete sleeper embedding wave type polymer concrete contributes to study of complex slab railway structures to minimize the vibration and noise generation from running trains.
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