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Keywords: floating slab track, vibrations, spring-mass system, finite element models.

Summary

Ground-born noise and vibration play an important role in the design of subway lines in urban areas. To avoid the effect of annoying vibrations, countermeasures are often necessary such as the use of resilient rail pads or floating slab track. This paper discusses the use of theoretical models to predict the vibration levels in floating slabs and the obtained attenuation.

One of the models is the one degree of freedom model. The transmissibility ratio was used to calculate the attenuation as a function of a normalized frequency parameter and the damping ratio. This attenuation was applied to the vibrations of a reference spectrum measured in a track with a stiff fixity.

A more complete model to evaluate dynamic behaviour of mass spring system is the double beam model. The first beam simulates the flexural stiffness and the mass of the rails and the unsprung mass of the train while the second beam simulates the floating slab properties. Two types of springs are used, one to connect the rails to the floating slab and the other to connect the floating slab to a fixed base.

To allow the simulation of tunnel mass and flexural stiffness, as well as soil properties (stiffness and damping ratio), a third beam and a third type of spring were added. With this approach the vibration levels in the tunnel invert could be estimated directly by the triple beam model (TBM). The implementation was through a time history analysis developed with the finite element method software SAP 2000. The dynamic forces of a measuring wheelset were used as the input data.

To evaluate the accuracy of both one degree of freedom and the triple beam model a case study using experimental data collected by the Company of São Paulo Metropolitan was developed.

The one degree of freedom model obtained conservative estimations for low frequencies and unconservative for higher frequencies (above 40 Hz). The global vibration level in the tunnel invert was overestimated in 10.3 VdB. Reasonable vibration levels for the rails, floating slab and tunnel invert were obtained using the triple beam model. The global vibration level in the tunnel invert was overestimated in 4.4 VdB. As well as the one degree of freedom model, the triple beam model underestimated the vibration levels for frequencies above 40 Hz.

From the results observed it is evident that further improvement is necessary with both models and will be implemented in the further development of this research project.

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Front Page Browse CCP CSETS CTR IJRT Other Authors Search Purchase Guide FAQ Contact us	Civil-Comp Proceedings ISSN 1759-3433 CCP: 98 PROCEEDINGS OF THE FIRST INTERNATIONAL CONFERENCE ON RAILWAY TECHNOLOGY: RESEARCH, DEVELOPMENT AND MAINTENANCE Edited by: J. Pombo Paper 108 Dynamic Behaviour of Reinforced Concrete Floating Slabs R. Carrazedo¹, J.T. Carvalho² and A.R. Takeuti² ¹São Carlos School of Engineering, University of São Paulo, São Carlos, Brazil ²Company of São Paulo Metropolitan - Metro, São Paulo, Brazil doi:10.4203/ccp.98.108 purchase the full-text of this paper Full Bibliographic Reference for this paper R. Carrazedo, J.T. Carvalho, A.R. Takeuti, "Dynamic Behaviour of Reinforced Concrete Floating Slabs", in J. Pombo, (Editor), "Proceedings of the First International Conference on Railway Technology: Research, Development and Maintenance", Civil-Comp Press, Stirlingshire, UK, Paper 108, 2012. doi:10.4203/ccp.98.108 Keywords: floating slab track, vibrations, spring-mass system, finite element models. Summary Ground-born noise and vibration play an important role in the design of subway lines in urban areas. To avoid the effect of annoying vibrations, countermeasures are often necessary such as the use of resilient rail pads or floating slab track. This paper discusses the use of theoretical models to predict the vibration levels in floating slabs and the obtained attenuation. One of the models is the one degree of freedom model. The transmissibility ratio was used to calculate the attenuation as a function of a normalized frequency parameter and the damping ratio. This attenuation was applied to the vibrations of a reference spectrum measured in a track with a stiff fixity. A more complete model to evaluate dynamic behaviour of mass spring system is the double beam model. The first beam simulates the flexural stiffness and the mass of the rails and the unsprung mass of the train while the second beam simulates the floating slab properties. Two types of springs are used, one to connect the rails to the floating slab and the other to connect the floating slab to a fixed base. To allow the simulation of tunnel mass and flexural stiffness, as well as soil properties (stiffness and damping ratio), a third beam and a third type of spring were added. With this approach the vibration levels in the tunnel invert could be estimated directly by the triple beam model (TBM). The implementation was through a time history analysis developed with the finite element method software SAP 2000. The dynamic forces of a measuring wheelset were used as the input data. To evaluate the accuracy of both one degree of freedom and the triple beam model a case study using experimental data collected by the Company of São Paulo Metropolitan was developed. The one degree of freedom model obtained conservative estimations for low frequencies and unconservative for higher frequencies (above 40 Hz). The global vibration level in the tunnel invert was overestimated in 10.3 VdB. Reasonable vibration levels for the rails, floating slab and tunnel invert were obtained using the triple beam model. The global vibration level in the tunnel invert was overestimated in 4.4 VdB. As well as the one degree of freedom model, the triple beam model underestimated the vibration levels for frequencies above 40 Hz. From the results observed it is evident that further improvement is necessary with both models and will be implemented in the further development of this research project. purchase the full-text of this paper (price £20) go to the previous paper go to the next paper return to the table of contents return to the book description purchase this book (price £110 +P&P)
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