| An aqueduct is an overhead flume that carries channel water across canals,valleys,depressions,and roads.Prestressed U-shaped aqueduct has the advantages of good modeling,superior water conservancy conditions,high structural stiffness and good stress conditions,and has been recognized and widely used in the industry.Once the aqueduct structure is damaged under the action of earthquake,it will cause great economic loss and serious social influence.The Standard for Seismic Design of Hydraulic Structures(GB 51247-2018)also puts forward new requirements for seismic design of aqueduct.Therefore,it is necessary to carry out the seismic research and evaluate the seismic performance of prestressed U-shaped aqueduct.This project carried out seismic vulnerability analysis and evaluation of prestressed U-shaped aqueduct based on fluid-structure interaction.The main research results are as follows:(1)According to the stress characteristics of prestressed U-shaped aqueduct structure,ANSYS finite element software is used to build a three-dimensional finite element aqueduct model with solid elements to simulate the aqueduct body and rack,three-dimensional fluid element to simulate the water body,linear elastic element to simulate the steel strand,spring element to simulate the rubber bearing,and beam element to simulate the action of pile and soil.The fluid-structure interaction was simulated by using the coupling surface of FSI-labeled water and aqueduct,and the pile-soil interaction was simulated by "P-y curve",which formed a 3D fine simulation model suitable for the seismic performance research of prestressed U-shaped aqueduct.(2)The effectiveness of the fluid-structure interaction model was verified through modal analysis of the convection-structure coupling model,the empty slot model and the unequal height shelving model at both ends,and the influence of the unequal height shelving at both ends on the natural vibration characteristics of the aqueduct was studied.The effects of water level,ground motion and two end supports on the seismic performance of aqueduct are compared and analyzed.The results show that: The transverse fluid-structure interaction effect of aqueduct is more significant.Compared with the empty channel without water,the transverse and longitudinal displacements and the first principal stress of the whole aqueduct are increased,the maximum transverse displacement is increased by 1.82 times,the maximum longitudinal displacement is increased by 0.18 times,and the mid-span tie rod bear a larger tension,which is 1.62 MPa,2.77 times.Fluid-structure interaction effect of aqueduct is also different under the action of different ground motions.The maximum longitudinal displacement of aqueduct under the action of Taft wave and Kobe wave is 2.12 times and 1.32 times of the transverse displacement respectively.However,the prestressed U-shaped channel has a large stiffness,and the peak value of the first principal stress at each position of the channel under the action of different waves is similar.There is a large stress concentration at the connecting beam and the bottom of the pier.The different rigidness of the unequal height arrangement at both ends amplified the fluid-structure interaction effect of the aqueduct.Compared with the equal height arrangement aqueduct,the transverse displacement and the peak value of the first principal stress at each position of the unequal height arrangement aqueduct at both ends increased by0.36 ～2.82 times,and the tension rod at the end of one side of the high pier was in a weak position,and the stress increased by 5.00 times.The longitudinal displacement process line has phase difference,and the displacement variation amplitude is within 2 mm.By studying the seismic response law of aqueduct under the influence of different factors,the seismic weak position of aqueduct is defined,which can provide reference for the seismic design of aqueduct.(3)Based on IDA’s seismic vulnerability method,the seismic vulnerability of each component of aqueduct under fluid-structure interaction is studied.The results show that the fluid-structure interaction improves the exceedance probability of the four limit states of pier,support and water stop.When the PGA is 0.5 g,the exceedance probabilities of slight failure,moderate failure,severe failure and complete failure at the design water level of the pier are increased by 2.94%,6.45%,1.09% and 0.11%,respectively,compared with the water-free condition.The support increases by 3.97%,3.08%,1.55% and 0.83%,respectively.Water stop increased by 31.95%,28.32%,26.65% and 15.76% respectively.Under the condition of slight failure and moderate failure,the failure probability of aqueduct pier is the largest,followed by water stop,and the failure probability of support is the smallest.The failure probability of aqueduct water stop is the largest,followed by support,and the failure probability of shelving pier is the least under severe failure and complete failure.For the aqueduct with unequal height arrangement at both ends,due to the stiffness change of the pier with unequal height arrangement at both ends,under the action of fluid-structure interaction,the transcendence probability of four limit states of low pier is greater than that of high pier,while the transcendence probability of water stop at one side of high pier is greater than that at the other side of low pier.The supports on high pier and low pier have safety reserves,and there is no obvious difference in the vulnerability curves of the supports on the two piers.In practical engineering,the seismic design of low frame pier and high pier should be considered.(4)The upper and lower bound values of seismic vulnerability of aqueduct system are obtained by the first-order bound method.The results show that the upper bound value of the failure probability of the most vulnerable aqueduct component only reaches the lower bound value of the failure probability of aqueduct system.Using the vulnerability of a single component to evaluate the vulnerability of aqueduct system will overestimate the seismic performance of the aqueduct system.Under the action of fluid-structure interaction,the system vulnerability of aqueduct system increases by 13.44%,9.03%,2.63% and 1.61% compared with that of empty aqueduct without water.Due to the different stiffness of high pier and low pier,the system vulnerability of the aqueduct with unequal height at both ends is increased by20.91%,16.24%,10.24% and 6.08% compared with that of the aqueduct with equal height.In the seismic design of aqueduct structure,the effects of fluid-structure interaction and the unequal height frame at both ends on the aqueduct should be considered.During the maintenance and reinforcement of aqueduct,it is important to consider the damage of water stop of equiheight arranged aqueduct and one side of high pier of unequal height aqueduct at both ends. |
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