Study On Adaptability Of Ground Exposed Steel Penstock To Fault Movement Displacement And Aseismic Behavior

The exposed steel penstock has straightforward bearing mechanism and is convenient for repair, so the type of ground exposed steel penstock is applied widely among actual projects, such as Tianhu, Nanshan first stage hydropower station and Zhangjiuhe water diversion project. Con-sidering the characteristics of wide coverage and open type, the geological condition of exposed steel penstock may be undesirable somewhere. In researches on buried pipeline used for water supply, oil transportation, communication and gas supply, study on fault movement attracts more attention. Compared with buried steel pipeline with small diameter, the exposed penstock with high head and large diameter is faced with more serious threat when traversing faults. The relia-bility of fault-crossing exposed steel penstock is urgent to be studied. Besides, earthquake disaster occurs increasingly frequently in recent years and aseismic behavior of exposed penstock is wor-thy of attention. Aiming at the two problems of fault movement and aseismic behavior, the pri-mary research contents are as follows with finite element method and engineering examples.(1) To reveal the mechanical characteristics and failure mode of exposed steel penstock under condition of fault movement, the typical layout,3-D entire mechanical model and fault movement were simulated exactly and the work performance of exposed steel penstock compo-nents was studied. The results show that, the displacement of steel penstock has different distri-bution law in each direction. In horizontal lateral and vertical direction, the displacement of steel penstock is the same as that of foundation. In axial direction, the displacement distribution is of sectional type. Affected by fault movement, the main elements of exposed steel penstock such as steel penstock, expansion joints and bearings are all likely to be damaged. The work performance of those elements is valued. If the magnitude of fault movement and friction coefficient of sliding support increases, the security and stability of structure will decrease. The initial static loads can increase sliding resistance force of bearing and considering that can reflect true mechanical char-acteristics of exposed steel penstock.(2) Based on the discussion of safety indexes for exposed steel penstock to adapt fault movement, two optimization schemes named fixation scheme and slide scheme and their applica-ble conditions were proposed. The results show that, when the axial displacement of each section of steel penstock is less disturbed by horizontal lateral and vertical displacement component of fault movement, there is no concentrated large deformation in axial direction and the deformation index meets requirement. If the magnitude of fault movement is small, the phenomenon of stress concentration will not occur and the bearing capacity index meets requirement. The fixation scheme is efficient only when the above two conditions are all satisfied. The slide scheme can weaken problems occurred in fixation scheme, so it is more favorable to adapt to fault movement for exposed steel penstock.(3) To study the aseismic behavior of above two optimization schemes, the seismic response and specific failure mode of the two schemes were considered with nonlinear dynamic time his-tory analysis method. The way of improving aseismic performance was discussed as well. The results show that, with fixation scheme, the pipe shell near hinged support has no enough strength reserve. The slide scheme has the impact on shock absorption and isolation and the pipe shell has enough strength reserve, but there is also a problem that the horizontal lateral deformation is too large. Setting caging device on sliding support based on slide scheme can hold both strength and deformation indexes. It is favorable for exposed steel penstock to adapt to both fault movement and earthquake action.(4) To study the travelling wave effect on seismic response of exposed steel penstock with long size in axial direction, nonlinear dynamic time history analysis method was used for dynamic calculation. The results show that, the travelling wave effect of seismic wave intensifies relative motion and expansion joints have large deflection. Due to the difference of input excitation be-tween sliding support and hinged support in each section, the relative displacement between steel penstock and sliding support increases. The relative displacement is adapted by both sliding sup-port and steel penstock, so the axial stress of steel penstock increases also. All above behavior influenced by travelling wave effect is more obvious when seismic velocity is less than 1 OOOm/s, so it is suggested that travelling wave effect should be considered under this condition.(5) To simulate the interaction between pipe structure and water, the fluid-solid coupling method was used. The influence of interaction between exposed steel penstock shell and water on dynamic characteristics and seismic response of structure were studied. The results show that, the mode considering interaction between fluid and solid is much different from that not considering water. Water is a factor that can not be neglected in obtaining dynamic characteristics of exposed steel penstock with thin wall. The dynamic water pressure on pipe wall is sensitive to frequency and amplitude of external excitation, the dynamic water pressure caused by resonant frequencies is 50 times that by non-resonant frequencies. The dynamic water pressure on pipe shell supported by hinged bearing and in area near anchor block is relatively large, the distribution is closely related with supporting system. The seismic displacement responses calculated by added mass method and fluid-solid coupling method have basically the same results. The seismic acceleration reaction of steel penstock and degree of stress concentration are enlarged by interaction between pipe and water. It is suggested that fluid-solid coupling method is more accurate in considering water influence when calculating aseismic behavior of exposed steel penstock.