Dynamic Response Analysis Of Cracked Lining In High-Speed Railway Tunnel Under Aerodynamic Load

With the development of high-speed railways,a large number of tunneling projects are inevitable.The fluctuations of piston wind and transient pressure during the high-speed entry and exit of trains into tunnels,as well as during t he passing and operation in the tunnels,are much more severe than those at l ow speeds.Assuming that there exist defects such as cracking or insufficient li ning thickness in the tunnel lining,the aerodynamic load characteristics of the cracked areas and the dynamic response of the lining with insufficient thicknes s would differ from intact linings when a train passes through,thus leading to new aerodynamic problems.Therefore,in-depth research on the aerodynamic lo ad spectrum characteristics of the cracked areas of tunnel lining caused by hig h-speed trains and the dynamic response of the detached and cracked tunnel li ning is of great economic value and social significance for ensuring the operat ional safety of high-speed railway tunnels,in order to explore the impact facto rs of aerodynamic loads on the severely cracked tunnel lining with insufficient thickness.Firstly,based on the theory of fluid mechanics,a numerical model of the entire process of a train passing through a tunnel was established using Gambi t.ANSYS Fluent was used to calculate and analyze the aerodynamic pressure on the tunnel wall under different working conditions,and the most unfavorabl e aerodynamic pressure spectrum was obtained.The calculated numerical soluti ons were compared with the results obtained from field measurements.Then,b y making a scaled model of the cracked lining in the tunnel,the previously c alculated time-domain pulsating air pressure function was processed and inputte d into the experimental pressurizing device to complete the loading process of the aerodynamic load.Real-time monitoring of the dynamic response of the ae rodynamic pressure and key points of the lining model was carried out by sen sors and software.Finally,using the APDL parameterized modeling and analysi s method of ANSYS software,numerical simulation wind pressure time series were added to different zones to solve the dynamic response of the detached a nd cracked lining in regions with insufficient lining thickness under different w orking conditions,and analyze the influence factors of the dynamic response o f the lining structure with insufficient thickness in regions of detachment and c racking under different train speeds and intersection situations.The results indicate that:(1)An increase in train speed and a decrease in the net cross-sectional area of the tunnel will cause an increase in the positiv e/negative pressure peak value at the cracked lining in the tunnel.Among the m,the relationship between speed and pressure peak value shows a quadratic f unction.The aerodynamic pressure peak value in a 92 m~2 tunnel is approximat ely 40%higher than that in a 100 m~2 tunnel.The uplift rate of the pressure peak value during train intersection is higher than 100%.The aerodynamic pre ssure peak value near the side of the train is higher than that far from the sid e of the train,with an enhancement range of 6.75%-43.75%.In the frequency domain,the frequency range with large pressure fluctuations mainly concentrate s in the low-frequency range of 0-3 Hz.With the increase of frequency,the s pectral density quickly decays to less than 40%of the peak value,and the fas ter the spectral density decays,the higher it is.(2)Under the action of aerody namic load,the first principal stress and vertical displacement of the cracked li ning exhibit obvious spatial and temporal distribution characteristics.The maxi mum value of the first principal stress appears at the midpoint outside the roo t of the cracked and detached lining,and shows outward annular distribution a round the maximum value,with a maximum value of 1.59 MPa.The maximu m value of the vertical displacement appears at the midpoint outside the end o f the cracked lining,and shows outward band-like distribution around the maxi mum value,with a maximum value of 1.42 mm.(3)The size has an obvious influence on the first principal stress of the cracked lining,and its variation la w satisfies the quadratic polynomial relationship.The stress change caused by every 0.25 m length change is above 0.25 MPa,the stress change caused by e very 2 circumferential angle change is above 0.02 MPa,and the stress change caused by every 1 cm thickness change is above 0.15 MPa.The influence of the loading peak value is:the stress increase caused by a change of 1 k Pa in the peak value is above 0.3 MPa.Due to the resonance effect,when the loadi ng frequency is close to the structural natural frequency,the first principal stre ss rapidly increases and exceeds the tensile strength of concrete,resulting in d amage to the lining.The influencing factors of the vertical displacement are c onsistent with the influencing factors of the first principal stress,and the variat ion law is opposite to that of the first principal stress,with similar amplitude change rate.