Design Of Modular Steel Structural Flexible Shed And Research On Its Anti-impact Performance

Shed tunnel is a passive resistance structure which is commonly used in the area where rockfall disasters occur frequently,such as tunnel entrances.It is mainly composed of supporting structure and buffer layer.The reinforced concrete rigid shed tunnel has a high level of resistance,but the shortcomings such as long construction period,occupied large area and high cost defects prominent,so it has lower cost performance.Relatively speaking,the steel structure flexible shed has the advantages of simple structure and lower costs.However,there are some problems such as fuzzy boundary between support structure and buffer layer structure,low protection level and low modularization degree,which lead to unclear division of key structural components in the system,frequent failure and damage of the whole structure,and high operation and maintenance costs.This thesis proposes a new type of modular steel structure flexible shed.The system has the characteristics of high modularity,high resistance level,and multi-layer resistance.By means of full-scale model test and numerical simulation,the impact resistance of the system was studied,and the force transmission mechanism,deformation characteristics and energy dissipation mechanism of the system were founded out.The main research contents of this thesis are as follows:(1)The research status and existing problems of the shed tunnel structure are analyzed and summarized(Chapter 1).This thesis systematically sorts out the engineering application and research status of the shed tunnel from the aspects of the structure system,protection performance and design calculation method,points out the defects of the existing system and the shortcomings of the research,and makes clear the research content and technical route of this paper.(2)The modular steel structure flexible shed tunnel system is proposed(Chapter2).The performance requirements of the structural design are clarified,design the modular steel structure flexible shed,describes the composition and structure of the system,and its working principle was clarified.(3)The full-scale impact test of the flexible buffer layer is carried out(Chapter 3).It reveals the whole working process and behavior curve of the flexible buffer layer under impact,analyzes the force,deformation characteristics and change laws of the system components in the three stages of relaxation,tension,and rebound,and clarifies the failure mode of the system and failure mechanism.The results show that the post of buffer layer presents a state of tension on the outside and compression on the inside during the impact process,and the test model has buckling failure due to the fabrication error.(4)The numerical model of the flexible buffer layer is established,and the energy dissipation distribution characteristics of the system are analyzed(Chapter 4).Based on the LS-DYNA program,a refined numerical model of the flexible buffer layer considering factors such as slip boundary,collision friction,and nonlinear deformation is established.The effectiveness of the model is verified by comparing with the experimental results.On this basis,analyzes the energy dissipation distribution law of the test model system and each component,and the energy dissipation mechanism and deformation characteristics of the system are revealed.The buckling of the buffer layer structure leads to the large energy dissipatio of the support component,which fails to give full play to the energy dissipation of the system.This situation should be avoided in practical application.(5)The full-scale impact test of the improved flexible buffer layer is carried out,and the influence law of key parameters on the impact resistance of the system is analyzed(Chapter 5).Carried out the full-scale impact test and numerical simulation analysis of the improved flexible buffer layer,the comparsion and analysis the flexible buffer layer before and the improvement revealed that the improved flexible buffer layer has higher energy dissipation efficiency and more stable structure;at the same time,it is proved that the deformation of the improved flexible buffer layer still has three stages of relaxation,tension and rebound.Analyze the impact of the key parameters of rock mass and speed on the impact resistance of the system,under the same impact energy,a with the increase of rock mass,the peak acceleration of the rock decreases exponentially,the maximum impact force of the rock and the total energy dissipation of the system increases gradually;and under the same mass of falling rock,with the increase of the impact velocity,the peak acceleration of the falling rock increases exponentially,and the impact force gradually increases.It is clear that the failure mode of the flexible buffer layer is mainly divided into the instability buckling of the support member and the fracture failure of the buffer member.The flexible buffer layer proposed in this thesis breaks under the impact condition of 3000k J,which reaches the ultimate bearing capacity of the system.