Study On Damage Effect Of High-Speed Railway Bridge And Tunnel Lap Structure Under Earthquake

The western and southern mountainous areas of China are located in the Eurasian seismic belt and the Pacific Rim seismic belt,and the seismic activity there is relatively frequent,and the earthquakes have occurred there frequently since modern times.Due to the special natural environment and complex geological conditions in mountainous areas,a large number of bridge and tunnel linked projects have been built in this area in recent years.Among them,due to the particularity of the structure of the bridge and tunnel linked projects,seismic fortification under earthquake is still an important issue to be solved urgently at present.Few scholars at home and abroad have carried out theoretical and experimental research on its damage effect,which hinders the engineering technology development of seismic fortification of the structure of the bridge and tunnel linked projects.Therefore,carrying out the research on shaking table model test and numerical simulation of bridge and tunnel lap structure is of great significance for the study of damage effect of bridge and tunnel lap structure under earthquake and seismic fortification measures.Based on the project of the National Natural Science Foundation of China,"study on seismic dynamic response of bridge and tunnel lap structures based on cumulative damage effect"(No.51408617),this thesis carries out the related theoretical analysis,numerical simulation and experimental research in respect with the damage effect of high speed railway bridge and tunnel lap structure under earthquake on the basis of reading a large number of relevant research literature at home and abroad by taking the lap structure of bridge and tunnel in southwest China as the engineering background.The main work and research contents of this thesis are as follows:It finds out the the dynamic response law of bridge and tunnel lap structure underearthquake and also reveals the dynamic damage and failure mechanism through the large shaking table test research and numerical simulation analysis based on the material damage theory,and then carries out the the comparative study of bridge and tunnel lap structure under lossless and damaged conditions through numerical simulation on this basis,and further finds out the shear stress variation law of tunnel lining section and bridge section,and also reveals its damage mechanism.Finally,it is found out that the numerical simulation results are in good agreement with the shaking table test results,which also verifies the reliability of the numerical simulation results.1.Damage Theory and Analysis method of concrete structures considering Seismic effect(1)It studies the application of strain equivalence hypothesis and stress equivalence hypothesis in damage analysis of concrete materials based on the definition of damage variable.(2)Based on the damage theory of concrete composite materials,it analyzes the influential effect that the compression resistance will decrease with the increase of deformation,as the pore volume in concrete material is decreasing in the process of compression.(3)Based on Resend’s theory of concrete damage analysis,it studies the general form of damage constitutive equation of concrete materials in the process of compression damage and tensile damage.(4)It studies the determination method of damage elastic modulus E=E E(1-D)in each computing unit,when we carry out the damage analysis of concrete element,so that the numerical simulation analysis of seismic damage of’bridge and tunnel lap structure can be effectively implemented.2.Shaking table test and research(1)It determines the similarity constant of the main physical quantities based on the similarity theory and experimental conditions.It also designs a high speed railway bridge and tunnel lap structure model with similarity ratio of 1:30 based on the purpose of experimental research.(2)It determines the similar material parameters of the model micro concrete and the material mix proportion of the simulated IV grade weak surrounding rock,and then prepares the experimental materials for simulating the IV grade weak surrounding rock through the proportioning test on the basis of determining the similarity ratio.(3)It determines the type of model box that is used in the test according to the purpose of the experimental study,and then determines the boundary treatment method of model test based on the test error caused by the boundary reflection problem of the model box used in the shaking table test(4)It selects the El Centro wave,Wenchuan wave and Taft wave as the experimental input seismic waves based on the adaptability and reliability of shaking table to seismic wave input,as well as the purpose of experimental research.Then it carries out the filtering processing on the input wave which does not meet the adaptability of shaking table.It determines the reasonable and feasible loading conditions of seismic wave on the basis of comprehensive consideration of the factors such as seismic wave type,shock intensity,loading direction and order.etc(5)It arranges the test points of the test model reasonably based on the purpose of the test study and the laboratory equipment conditions.It measures the dynamic responses such as dynamic stress,dynamic strain and dynamic acceleration in various parts of bridge and tunnel lap structure accordingly under different working conditions.(6)It studies the dynamic response law of high speed railway bridge and tunnel lap structure under test conditions based on the analysis and research of the test results of large shaking table.It analyzes the dynamic damage and failure mechanism of high speed railway under the action of the earthquake,and it also make further analysis on the seismic fortification measures of bridge and tunnel lap structure on this basis.3.Numerical simulation research(1)It establishes the 3D numerical simulation model of bridge and tunnel lap structure based on the model test and practical engineering.(2)It conducts the comparison analysis on the result of shaking table test and the numerical simulation results,thus verifying the reliability of the numerical simulation results(3)It analyzes the shear stress of bridge and tunnel lap structure under lossless and damaged conditions by changing the elastic modulus of damage E~E(1-D),based on the structural damage theory.We obtained the following research progress and innovative conclusions through the above research.(1)It finds out the variation law of dynamic acceleration response of each measuring point of bridge and tunnel lap structure under the action of El Centro waves in different loading directions.The results show that the seismic wave has the greatest superposition amplification effect when the seismic wave is superimposed by bidirectional loading in the horizontal direction.(2)It finds out the dynamic acceleration response of bridge and tunnel lap structure under the action of different kinds of seismic waves with the same intensity.Under the action of different kinds of seismic waves with the same intensity.The results show that different carrier has little direct effect on the acceleration response,but only slightly different from the peak value of acceleration.(3)It reveals the law of acceleration change of bridge and tunnel lap structure shows the mechanism of three-stage damage and failure under the action of different peak seismic waves.(4)It finds out the dynamic strain response law of the tunnel part of the bridge and tunnel lap structure under the action of different excitation peak earthquakes of X direction Wenchuan wave.Through the study,it is found that the longitudinal dynamic strain response of the extended section and the tunnel structure is obviously larger than that of the circumferential dynamic strain response.(5)In the lossless state,the shear stress of tunnel lining of bridge and tunnel lap structure shows a similar changing trend under the action of seismic waves with different shock peaks.There is only a significant difference in the size of the shear stress.However,the shear stress increases with the increase of the peak value of the shock,and the shear stress increases most obviously at the arch shoulder.(6)The variation of shear stress of tunnel lining in damaged state is similar to that in lossless state under the action of the same peak seismic wave.However,the shear stress of the lining decreases with the decrease of the effective elastic modulus E(namely,the elastic modulus E after damage).(7)The shear stress of the bridge section of the bridge and tunnel lap structure shows the trend that the two segments are small and the span is large both in a lossless state and in a damaged state.The range of the maximum shear stress does not increase with the increase of the peak value of the shock and the degree of damage,and there is only a significant increase in the value of shear stress.What’s more,the greater the degree of damage,the greater the increase of shear stress.The above research results lay an experimental foundation for the establishment of seismic damage analysis theory of bridge and tunnel lap structure and also provides a theoretical basis for seismic fortification of bridge and tunnel lap structures.It has important theoretical significance and has broad engineering application value as well.