Seismic Analysis And Shaking Table Test For Ultra-large Cooling Tower Structure

As the request of national environmental protection strategy, some 1000 Mw supercritical air-cooling units are to be built in the Three-North Regions of China. The height of corresponding air-cooling towers is usually more than 200 meters and the diameter of the tower maybe larger than 180 meters. Relevant air inlet is higher than 30 meters. Most of the cooling towers will be built in the central and northern part of the South-North earthquake belt. Its site conditions are extremely complicated and seismic hazard is quite high. The seismic design of these cooling towers has to deal with questions such as high intensity, soil-structure interaction, traveling wave negative effect and so on. However, engineering researches on seismic design of the ultra-large cooling towers are very rare, not to mention reference materials. In order to solve the problems, this paper mainly focuses on the seismic failure mechanism of the ultra-large cooling towers with shaking table test and numerical simulation analysis. Furthermore, the paper researches and discusses soil-structure interaction, traveling wave negative effect and the feasibility of base isolation. The main work in this dissertation includes several aspects as follows:1. 1:30 scaled insufficient-mass shaking table test model was designed for the ultra-large cooling tower shaking table test based on method of similar ratio theory. The prototype of the model is 200 meters high and 188 meters span. By the shaking table test, the dynamic responses of the scaled model and its failure characters under various earthquake conditions, considering different intensity and site conditions, were researched,The seismic failure mechanism of the ultra-large cooling towers was revealed. Both ends of the X braces are the weak parts of the ultra-large cooling towers in earthquake. This discovery will contribute to the seismic design of such ultra-large cooling towers. The numerical simulation analysis also verifies the reasonability of the finite element numerical simulation.2. The paper proposes a parameter αs to modify the lateral maximum seismic influence coefficient αmax of the design spectrum in order to simplify the design procedure easily considering the effect of soil-structure interaction in site II and III for large and high structure. Viscoelastic damping element was used to simulate the foundation boundary. The dynamic responses of the ultra-large cooling tower, considering the soil-structure interaction,were simulated and compared with the responses without considering the soil-structure interaction structure. The dynamic response rules of ultra-large cooling tower, in site II and III, should be given special focus.3. This paper proposes a parameter αT to modify the lateral maximum seismic influence coefficient αmax of the design spectrum in order to simplify the design procedure considering traveling wave negative effect. The paper analyzed the dynamic response of the ultra-large cooling tower both considering the soil-structure interaction and traveling wave effect or not. Analysis results shows that if the tower being built on site I and corresponding apparent wave velocity ? 1000 m/s the traveling wave effect might be neglected. Otherwise, apparent wave velocity ? 350 m/s, it is necessary and important to consider the traveling wave effect in site II and III.4. The paper recommends isolator analysis method used to degrade the responses of the ultra-large cooling tower in high intensity earthquake area. The paper researches on the effect of base isolation by finite element method under different conditions involving soil-structure interaction, traveling wave negative effect. 8, 9 rare intensity numerical results indicate that the relative displacement, acceleration and the drift angle of X braces decrease significantly and this undoubtedly ensures the safety of the ultra-large cooling towers.