Seismic Response Of Large Hydraulic Structure Of Inverted Siphon

The water resources is very rich in our country, but the distribution of water resources is very uneven, so it is so much important to achieve the rational allocation of inter-basin water resources by large-scale water diversion project. The South-to-North Water Diversion is the largest water diversion project under construction currently, it can effectively alleviate the acute shortage of water resources in northern, while, large inverted siphon structure is widely used in water diversion project serving as the overpass structure, especially the inverted siphon which is used when the channel through the valley. Large flow, large sizes and Large Span are its salient features, and most of them lie in a high seismic area. Therefore, it has a huge economic and social benefits to make sure the safe operation of these inverted siphon structure when encountering the earthquake in the future.China is an earthquake-prone country, at the same time, most of the channel inverted siphon are located in the high seismic area, so these structures can easily encounter the near- field and far-field earthquake. The near- field earthquakes usually include the velocity and displacement pulse, this can make the structure suffer strong shock at first and cause strong internal force, large deformation and displacement, while, the far- field earthquake has a rich long-period component which is likely to cause resonance phenomenon because that the long-period component has a similar or consistent cycle with the overall soil-structure system of lagre channel inverted siphon, the resonance phenomenon may damage the structure seriously.The paper relies on the construction background of the South-to-North Water Diversion and make the channel inverted siphon structure as the research object. Taking the soil-structure interaction as the theory and considering the influence of hydrodynamic in the pipeline, a interaction model for inverted siphon structure is built based on the finite element software ANSYS. Using this model, we can analyze the dynamic response of inverted siphon structure under the ground motions of two different spectral characteristics of near-field and far-field earthquake. Due to the inverted siphon structure usually contains horizontal sections 、 inlet and outlet transition section, so two-dimensional and three-dimensional models of Horizontal section and three-dimensional model of inlet transition section are created respectively for dynamic response analysis in this paper, the conclusions are as follows:(1)The water in the pipeline can decrease the amplitude of each vibration mode of the overall soil-structure system, and the more pores that water goes through, the smaller amplitude of each vibration mode.(2)Under the scenario earthquakes of the near-field and far-field excitation in this paper, the structure has a great absolute displacement in horizontal which is likely to cause dislocation damage in the interface of the pipeline, I n addition, the vertical component of the near- field earthquake also cause significantly absolute displacement in the vertical, so it is necessary to consider the vertical component of the earthquake when analyzing the dynamic response under the near-field earthquake excitation.(3)Under the scenario earthquakes of the near-field and far-field excitation in this paper, the extreme values for tensile and compressive stress of all the different models do not both reach the structural tensile or compressive strength, therefore, the structure will not occur tensile and compressive stress failure, however, the extreme value for tensile stress of three-dimensional model of inlet transition section is larger than 1MPa which has a same magnitude with the structural tensile strength of 2.05 MPa, it can cause tensile stress damage, such as the tension crack.(4)Under the scenario earthquakes of the near-field and far-field excitation in this paper, displacement and stress time-history curves both exist sudden jump phenomenon in the dynamic analysis, especially in the stress time-history curves of the three-dimensional models of Horizontal section under the ground motions of the far- field earthquake. This sudden jump phenomenon of displacement and stress has something to do with the pulse effect of the near- field earthquake and transient resonance phenomenon that is caused by the far- field earthquake, and this sudden jump phenomenon can make a big damage to the structure.(5)Hysteresis phenomenon in the dynamic response of inverted siphon structure is also very significant, for example, the peak time of absolute displacement、tensile and compressive stress log behind that of peak acceleration, which should because that the small elastic modulus of the soil and that the soil absorbs some energy of the earthquake.