Study On Structural Dynamic Damage Law And Seismic Fragility Of Large-sized Aqueduct For South-north Water Diversion Project

The Middle Route Project of South to North Water Diversion plays a key role in solving the uneven geographical distribution of available water resources in China and promoting the sustainable development of life,economy,ecology and environment in water shortage areas.It is a national strategic project beneficial to the country and the people.With the operation of the Middle Route Project of South-to-North Water Diversion,the effect of water resources allocation has become increasingly prominent,and the gradual increase of water supply not only optimizes the uneven distribution of water resources in China,but also effectively promotes the construction of ecological civilization in China.In the construction of the Middle Route Project of South-to-North Water Diversion,aqueduct plays an important role as a link and occupies an indispensable position.The dynamic response law of aqueduct under earthquake load is also focused by scholars.At present,the seismic research of aqueduct structure is still reflected in the application of numerical simulation method.In the nonlinear analysis,solving the boundary condition problem is still the key step of seismic research.Moreover,it is more conducive to study the safety and stability of the structure to pay attention to the damage characterization under different ground motion excitation,which will have important theoretical and engineering reference significance.Based on this,this paper intends to use a variety of boundaries to simulate the infinite foundation of a large aqueduct structure in the South-to-North Water Diversion Project,to reflect the energy dispersion phenomenon of waves in different boundaries,to study the dynamic failure development law under rare earthquakes,and to obtain the weak seismic parts that should be paid attention to;The measured ground motion records which meet the calculation conditions and the artificial waves which are in good agreement with the actual engineering site response spectrum are selected for unequal step amplitude modulation and nonlinear dynamic analysis respectively;Applying the response index suitable for evaluating the aqueduct structure,quantifying the ultimate failure state of the structure,constructing the fragility curve reflecting the deformation capacity of the aqueduct structure,describing the specific failure degree of the aqueduct structure under the transcendental probability,providing reference for the normal operation of the aqueduct structure.The research content is mainly divided into three parts,including the infinite domain foundation simulation under different boundary conditions and the dynamic damage development law of large aqueduct foundation coupling system under rare earthquake,the selection of seismic fragility analysis method suitable for aqueduct structure,the determination of response index to evaluate aqueduct structure and the construction of fragility curve reflecting structural deformation capacity.The specific research results mainly include the following parts:(1)This paper expounds the research status of water conservancy engineering in the field of earthquake resistance,involving the position and research value of the typical building large aqueduct structure in the field of earthquake resistance;The research status of seismic calculation boundary and seismic fragility,related application methods and the development trend of hydraulic engineering buildings in this field are described;(2)The calculation model of aqueduct foundation structure coupling system is established,and the natural vibration characteristics of the structure are studied by using the basic theory of structural dynamics.The calculation results verify that the aqueduct structure selected in this paper meets the general law of structural dynamics;(3)It illustrates the fixed boundary,viscous-spring boundary,the basic theory of infinite element boundary,which implements the method described in detail;The model of aqueduct foundation structure coupling system is established to study the wave energy absorption and reflection effect of each boundary;The plastic damage constitutive model of concrete is introduced to analyze the nonlinear characteristics of aqueduct structure under rare earthquake,and to find the development law of structural damage and damage and the evolution process of dynamic damage under strong earthquake;The results show that under the action of strong earthquake,the possible damage parts of large aqueduct structure are mainly concentrated in the top of the aqueduct body,the bottom of the pier cap,the top of the pier body and the side of the pier body.These areas should be the weak points of the seismic design,and the reinforcement or section design should be strengthened to control the development of structural dynamic damage and prevent the overall failure of the structure;(4)Based on the response spectrum of aqueduct engineering site,according to the spectrum similarity characteristics,magnitude,duration and other factors,the actual natural seismic waves which meet the calculation conditions and the artificial waves which are in good agreement with them are selected,and the spectrum acceleration is taken as the seismic intensity index to carry out the dynamic analysis of seismic waves with unequal step amplitude modulation and non-linear increment;(5)In order to reflect the damage characterization of aqueduct structure under different seismic excitations,the response index suitable for aqueduct structure evaluation is selected.IDA and MSA seismic fragility analysis methods are introduced to construct the seismic fragility curves reflecting the deformation capacity of aqueduct structure;(6)Comparing the two fragility analysis results,it is shown that in seismic analysis,aqueduct structure will be difficult to maintain intact state;MSA method is used to calculate the number of seismic waves which depend on exceeding the limit value,and limited by the number of selected seismic wave samples.IDA method mainly depends on the logarithmic mean value and logarithmic standard deviation of structural engineering requirements parameters.The overall fragility results agree well,and the curve change rules The law is basically consistent;the two fragility methods have their own characteristics.Although IDA method is simple in theory,it is more complex to process data and the theory of MSA method is more complex.However,in the nonlinear response analysis,only the seismic strength exceeding the response value of the structure can be calculated in this paper;(7)By introducing two kinds of seismic fragility analysis methods,the rationality of seismic fragility results of aqueduct structure is verified,and the limit states of aqueduct structure under different seismic intensity are accurately identified,and the specific damage degree of aqueduct structure under exceeding probability is described,which provides suggestions for seismic damage analysis and safe operation of aqueduct structure.