| The seismic response of long-line underground structures like tunnels is affected by the spatial changes of site motion,so the longitudinal seismic response is the focus of their seismic analysis.The response displacement method has been adopted by many countries and applied to many practical projects because of its clear concept,simple operation,and excellent accuracy.Based on the combination of theoretical analysis and numerical simulation,after a comparative study of the longitudinal response displacement method,this paper proposes a simplified method for longitudinal seismic analysis of underground structures in complex sites.In addition,in terms of the difficulties of practical engineering application,an interface software for the longitudinal seismic analysis of shield tunnels based on the response displacement method was developed on ABAQUS.The main research content and results of this paper are as follows:(1)Based on the theory of beam bending and the basic assumption that the deformation of the underground structure is mainly affected by the deformation of the soil layer,a simplified method suitable for the longitudinal seismic analysis of underground structures such as tunnels in complex sites is proposed.This method firstly performs numerical differentiation on the free field displacement time history at the axis of the structure under the action of an earthquake.This data processing can directly determine the soil deformation curve corresponding to the maximum internal force of the structure.Then,the deformation curve will be applied as an equivalent seismic action to the non-structural end of the foundation spring of the response displacement method model.After solving in the static mode,the maximum internal force of the underground structure is obtained.Taking a shield tunnel in a longitudinal section of a complex soft soil as an example,the longitudinal generalized response displacement method and the simplified method proposed in this paper are used for seismic analysis.Moreover,this project is used as a background to study possible factors that affect the error of the simplified method.The research results show that the simplified method proposed in this paper is simple,efficient,and has good calculation accuracy and stability.The average error rate of bending moment and shear force is less than 5%,and the results of positive and negative axial force are approximately 6% and 25%respectively.The error of the maximum internal force calculated by the simplified method decreases significantly with the increase of the hardness of the site,indicating that the new method has high engineering application value.(2)Using the secondary development interface of the finite element software ABAQUS,the calculation software for the longitudinal response displacement method of the shield tunnel was developed,which including the traditional longitudinal response displacement method,the longitudinal generalized response displacement method and the simplified method proposed in this article.This software can not only receive the free field displacement time history specified by the user,but also call the equivalent linear analysis program of one-dimensional formation seismic response to calculate the seismic response of layered soil.According to the engineering parameters,the longitudinal "beam-spring" finite element model of the shield tunnel is created,which including non-linear connection springs between the shield rings and foundation springs arranged in the longitudinal direction of the model.On this basis,the site displacement is applied as an equivalent seismic action to the reference point of the foundation spring.After the solution is automatically submitted,the software will directly output the results of the tunnel internal force and displacement,realizing the automation of the entire process.At the same time,combined with the engineering example data in the literature,the accuracy and reliability of the software in this paper are verified. |
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