Study On Nonlinear And Seismic Response Of Flow Channel Structure In Bulb Tubular Turbine Hydropower Station

The development of low-head hydropower resources is still low,and the tubular hydropower station has an irreplaceable role and advantage in the development of low-head water resources.The powerhouse of bulb tubular turbine hydropower station is not only a power generation building but also a water retaining building,which is widely used in riverbed-hydroelectric station.In the design of the bulb tubular turbine hydropower station,which connection mode of the new and old concrete,the mechanical and damage characteristics of the concrete in tubular pedestal of unit,and the anti-seismic behavior of the powerhouse structure are all the focus in engineering construction.Therefore,based on an actual engineering of a bulb tubular turbine hydropower station,which the contact nonlinear analysis between the new and old concrete,the material nonlinearity analysis of the concrete in tubular pedestal and the seismic time history analysis of the GIS room structure are researched.The main research contents are as follows:(1)The contact nonlinear analysis theory was carried out to study the structural mechanical characteristics between new and old concrete of the flow channel under different connection modes.As the results show that it is better to adopt the planting reinforcing bar scheme than that adopt the artificial chiseling or interfacial agent scheme.After reinforcing bars are embedded in the interface between new and old concrete,the integrity of the first and second stage concrete is enhanced,and the bond-friction characteristics between the new and old concrete can be fully utilized to reduce the value and range of the tensile stress in the second-stage concrete,and the stress and displacement laws obtained by this scheme are similar to those of the concrete casting scheme.(2)Through the joint surface optimization scheme and the deep analysis of the reinforcement planting rate show that the first-stage concrete of this scheme can provide greater resistance,which is beneficial to reduce the tensile stress value and distribution range of the second-stage concrete,and reduce the deformation.The suitable rate of reinforcement planting is not only conducive to enhancing the concrete integrity of the first and second stage concrete of the flow channel,improving the combined bearing capacity,but also reducing the gap of the concrete joint surface.Therefore,it is recommended to adopt the type of joint surface optimization scheme,considering the planting reinforcement,so as to fully exert the concrete resistance and ensure the normal operation of the unit.(3)Considering the material nonlinearity of tubular pedestal concrete and the combined bearing capacity of the reinforcement,a deeper analysis of the tubular pedestal concrete is carried out.As the result shows that the damage area of the tubular pedestal concrete is mainly concentrated in the downstream top and bottom of the tubular pedestal concrete in flow channel and downstream turning point of hanging hole of generator unit.The damage area first developed along the tubular pedestal column holes,and penetrating damage occurred at the downstream of the column holes,and the damage value at the top of the flow channel was greater than that at the bottom,while no obvious damage was observed at another parts of the concrete.In addition,the proper optimization of the reinforcement ratio of tubular pedestal concrete is conducive to give better play to the joint bearing characteristics of reinforced concrete.(4)Through the analysis of concrete overload of tubular pedestal,it is found that with the overloading of the internal water pressure,the whole penetrating crack is first produced on the downstream side of the column hole of the tubular pedestal concrete,and there is a wide range of damage in the top,bottom and thickness variation area of the tubular pedestal concrete.When the internal water pressure reaches 4.0P,the lateral waist of both sides will suffer tensile damage due to large deformation,at which time reached reinforcement yielding.According to the analysis of overload capacity,the displacement value of the characteristic point shows a linear change with the load.The concrete structure of the tubular seat has a large overload capacity,and the overload coefficient is above 3.83.(5)After analyzing the seismic response of the powerhouse structure,it was found that the nonlinear characteristics of the real simulated concrete are beneficial to analyze the damage value and damage position of the structure,analyzing the structural damage,making a reasonable seismic performance evaluation.When the powerhouse structure is subjected to different earthquake with peak acceleration,while the reinforcement has not reach reinforcement yielding,the dynamic displacement of the structure increases linearly with the increase of the peak acceleration of the earthquake,and the sensitivity of the vertical dynamic displacement of the GIS room structure is lower(6)Through the self-vibration analysis and resonance check of the whole powerhouse structure,it is found that considering the cracking of concrete will reduce the natural vibration frequency of the structure.Especially for larger damage after considering concrete material nonlinearity of GIS room,when there is a single mode in the GIS room,the natural frequency decreases obviously,but it has less influence on the overall mode.