| As an old saying goes,“Construction before being rich and sufficient”.If the 21 st century is the era of the great rejuvenation of China and the Chinese,it must be the construction sound of transportation engineering,and the roar of city subways,metro lines,high-speed trains and other means of transportation that accompany with the rising of Chinese Dream.According to related data,the mileage of China's operating railways and high-speed railways has been ranked first in the world for long.In 2019,the total mileage of China's high-speed railway in operation has reached more than35000 km,and the highest designation speed of the high-speed railway under construction has reached 400 km/h.With the acceleration of urbanization and increasing of urban population,the total number and coverage of subways and metro lines in major cities of China keep expanding.By the end of 2017,34 major cities have operated their city subways or metro lines.Behind the accelerated development of industry and the global trend of “made in China”,the amounted of industrial facilities and equipments are running with full speed.With the rapid development of transportation and industry,the vibration problems caused by subway,metro lines,high-speed trains and mechanical equipment have attracted attentions.For example,Beijing subway line 4 has affected the precision of researching instruments in Peking University,and Chongqing metro line passes through buildings in Liziba station.To investagate the propagation law of vibration,and to take specific vibration isolation measures,are of great social significance and economic value nowadays.Unfortunately,the research on vibration and wave propagation is not enough for engineering.There are still shortcomings in related researches:(1)The conclusions based on engineering experience are not accurate enough to apply in other cases.The law and mechanism of wave propagation are not revealed;(2)Theoretical research only solved one single problem for once.There still lack of a general solution that can be applied to solve different problems;(3)The research of numerical simulation method is mostly based on three-dimensional element,which takes too much time in the calculation and simulation,and is inefficient.Based on the above situation,this paper has conducted a comprehensive and deep study on the system response caused by dynamic load applied on the surface of semi-infinite space.The research mainly includes the following parts,and has achieved some innovative results and conclusions:(1)Based on the triple Fourier transform,the theoretical closed solution of the response of the semi-infinite space is derived from the equilibrium differential equation and the stress-strain equation of elastic half space.By demonstration and illustration of case study,it is showed that the closed solution can simultaneously solve the dynamic response of semi-infinite space caused by external loads with various of distribution and motion forms.The solution acquired in this paper is general and can reveal the mechanism of dynamic response of semi-infinite space;(2)The 2.5D numerical approach proposed by Yang in 2001 is involved and discussed in this paper.The 2.5D program is built.By comparing the numerical and theoretical solutions,the 2.5D approach which is only used to study the dynamic response of semi-infinite space caused by straightly moving loads,is innovatively extended and deeply investigated.In this paper,the 2.5D approach is applied to solve the problems of fixed harmonic load and the curved moving load;besides,the stress and strain response in semi-infinite space can also be obtained by present method;(3)An amount of examples are calculated and discussed.The laws and special phenomena of dynamic response in semi-infinite space are summarized,analyzed,and explained.For example,the wave propagation condition,propagation angle,Doppler effect,critical speed effect and system response induced by centrifugal load of curved moving load are discussed.(4)A large number of numerical experiments of parameter studies are conducted to analyze the vibration isolation efficiency of various of measurements to vibration sources.Empty trench,in-filled trench and rigid foundation are involved as typical measurements.Conclusions obtained can be referenced by engineering practice.It is found that the wave with low frequency has strong ability to pass through isolations.Among the measurements discussed in this paper,one should focus on the depth of vibration isolation measures,and the vibration isolation measures close should by designed close to the construction to be protected. |
PDF Full Text Request