Study On Flexible Seismic Isolation Optimization And Seismic Reliability Of PCCP Under Multi-Field Coupling

PCCP(Prestressed Concrete Cylinder Pipe),as an important part of underground lifeline engineering,has been widely used in large-scale water diversion projects,many of which pass through high-intensity seismic areas.Because PCCP is a multi-material layered composite structure,coupled with the randomness of seismic excitation,the failure mode and reliability prediction of the structure during operation become complicated.At present,there is a lack of research on the seismic response of PCCP structures and their seismic mitigation and anti-seismic aspects during the operation period.Based on this background,this dissertation explores the response of PCCP structures under random earthquakes during operation combining theoretical,numerical,and full-scale experimental methods,and then carry out the structural outsourcing seismic isolation layer seismic optimization design and seismic reliability research,which provide reference for the seismic optimization design of underground pipeline structures.The main research results of the dissertation are as follows:(1)A three-dimensional refined PCCP pipe soil structure equivalent linear viscoelastic ground vibration analysis model containing the pressurized fluid inside the pipe,the stiffness contribution of each structural layer,and the double rubber ring multi-pipe section socket connection is constructed and validated by full-scale model experiment.Further research on the dynamic response of the structural layer of PCCP under the coupled action of multiple fields such as operation,site and earthquake is carried out,and the results show that:Both the pressurized water inside the pipe and the seismic peak acceleration have a great influence on the PCCP structure,and the influence of the internal water pressure on the stress state of the structural layer is very obvious,but the influence of the water flow velocity on the stress state of the structural layer is weak;the soil pressure around the pipe has a greater influence on the deformation and stress of the structural layer close to the soil side,while it has less influence on the structural layer far from the soil side.(2)The dissertation proposed a method of wrapping a flexible seismic isolation layer outside the PCCP structure to reduce the seismic damage to the pipeline and established a three-dimensional dynamic finite element model of the interaction of"soil-seismic isolation layer-pipe structure".The model analyzed the influence of parameters such as the material density,thickness,shear modulus and damping ratio of the seismic isolation layer on the seismic isolation effect.The results show that the greater the thickness of the flexible seismic isolation layer,the smaller the density and the shear modulus,the better the seismic isolation effect,and the influence of the damping ratio on the effect is less.(3)The dissertation proposed the multi-objective optimization design method for the externally wrapped seismic isolation layer of the PCCP structure and defined the concept of PCCP structure safety margin.An optimization model of the relationship between the seismic safety margin of the PCCP structure and the design variables of the flexible seismic isolation layer is established to realize the optimal design of thickness,density,and dynamic shear modulus of flexible seismic isolation layer under seismic loads.The results show that the thickness and shear modulus of the seismic isolation layer have a greater impact on the safety margin of the seismic performance of the structure,while the density has a smaller impact.(4)The dissertation proposed a method for analyzing the seismic reliability of PCCP structures under random ground vibration excitation.Combining the probability density evolution theory and the physical model of engineering random ground motions,the stochastic seismic dynamic response and seismic reliability of PCCP structures with and without flexible vibration isolation layers are compared and analyzed.The results show that:with the increase of ground motion excitation,the degree of variation of the seismic response of the PCCP structure also increases,and the randomness of ground motion cannot be ignored;The seismic reliability of the structure decreases with the decrease of the failure threshold;After the structure is wrapped with a seismic isolation layer,its seismic reliability is significantly improved.