Study On The Influence Of Excitation Modes On The Evaluation Of Vibration Mitigation Performance Of Floating Slab Track In Metro

With the rapid development of metro construction in China,the public travel is facilitated,but increasingly serious environmental problems are also induced,such as vibration and noise,which has aroused strong public response.Among various of vibration mitigation measures,track vibration mitigation measures have the widest application scope and obvious effect.As the vibration mitigation effect of a type of track vibration mitigation measure is not its inherent characteristic,but strongly affected by its the boundary condition and load condition(excitation mode,preloading,etc.).However,there are few studies on the effects of boundary conditions and load conditions on the vibration mitigation performance of track structures.The research of this thesis was obtained the financial support of National Natural Science Foundation of China(No.51508022):"Study on the evaluation method of vibration mitigation effect for metro isolated tracks based on the fixed-point impulse test".In this thesis,the floating slab track(FST)is selected as a typical track mitigation measure.The insertion loss is used as an evaluation index of vibration mitigation effect.Both field test and numerical simulation were used for the quantitatively studies.The main work performed and research conclusions drawn of this paper are as follows:(1)Vibration source tests in tunnel were carried out under two different excitation modes:the impulse loads and moving train loads.The test results indicate that the vibration responses on the tunnel wall under the impulse loads are more discrete than those under the moving train loads in the frequency band below the natural frequency of the steel spring FST.Below the natural frequency of the steel spring FST,the comparative loss value tends to zero under the impulse loads,and it is almost negative under the moving train loads.Compared with the excitation by moving train loads,in all frequency bands,the vibration mitigation effect of steel spring FST will be overestimated by impulse loads.(2)A vehicle-track-tunnel-soil coupled numerical model was established by using ABAQUS finite element software.The model was validated based on field test data.The results show that the calculated results are in good agreement with the measured ones.(3)The vibration mitigation performance of steel spring FST under different types of excitation modes is numerically calculated and analysed.The results show that the natural frequencies of FST under different excitation modes are between 8 and 10 Hz,which is consistent with the field test results.When calculating the dynamic response of track structure by using the method of moving load excitation,the element size should be refined reasonably to avoid the influence of the characteristic frequencies.By applying impulse loads the vibration mitigation effect of this FST may be overestimated.(4)The numerical calculation and analysis of the vibration mitigation performance of the FST under different excitation modes are carried out.The results show that the natural frequencies of the FST are 23-25 Hz under different excitation modes,and the insertion loss value under impulse load excitation is positive in the frequency band below 5 Hz,and the insertion loss under moving load and moving vehicle load excitation is positive.The loss value is negative,which is the same as the trend of the steel spring FST.Compared with the other two excitation methods,the impulse load excitation method may overestimate the vibration mitigation effect of the FST in most frequency bands.