Study On Key Issues Of Seismic Design Of Extra-Large Reinforced Concrete Cooling Tower Structure

With the increase of China’s power supply demand and the improvement of environmental protection requirements,domestic thermal power plants have begun to seek the construction of extra-large concrete cooling towers with a height of more than 200 m.However,there is not much systematic research on the seismic performance of extra-large cooling tower structures in high-intensity areas.X columns with large slenderness ratio,as the most critical components that affect the safety of extra-large cooling towers,have not been found to be studied in detail by domestic and foreign scholars.Intensive study on the vibration response characteristics,damage modes,weak parts and key component design methods of extra-large reinforced concrete cooling tower structures under seismic action is of great significance for guiding the seismic design of such structures.At the same time,seismic isolation technology has high shock absorption performance,while it has not been found any research on its application in the extra-large cooling tower structure in the high-intensity area.In this paper,the above issues are studied through shaking table tests of the overall model structure of the extra large concrete cooling tower,the quasi-static tests of X columns and numerical simulation.The main contents,methods and results are as follows:(1)The seismic simulation shaking table tests of the scale models of isolated and non-isolated extra-large cooling towers was carried out.Considering the dynamic similarity law,a 1/30 scale model of an extra-large cooling tower structure of nearly 200 m in the fortification area of 8 degrees(0.3g)was made using a new type lead-iron powder-based aggregate concrete,and the isolation design was carried out.Seismic simulation shaking table tests were carried out on the isolated model and the non-isolated model.The test results revealed that the X columns were the weak parts of the cooling tower structure,and the top of the columns were the first to be destroyed under the action of earthquake.The non-isolated cooling tower model was generally cracked and destroyed at the top of the column under the seismic action of fortification level.Under the rare earthquake condition,the concrete at the top of the X columns was obviously crushed and exposed,and horizontal cracks along their whole length appeared.Taking the isolation measures using lead rubber bearings can significantly reduce the acceleration and displacement response and damage degree of the extra-large cooling tower structure under seismic action,and the horizontal seismic isolation effect can reach 50% for the vibration response at the top of X columns.(2)Quasi-static tests on the scale models of X columns with large slenderness ration in the extra-large cooling tower were carried out.Quasi-static tests of four 1/8 scale models of 40 m high X columns and double-cross columns were carried out on four forms of columns with the difference of continuous and discontinuous longitudinal reinforcements at the intersection.Horizontal loads were applied at the top of X columns out of plane,and tension or compression was applied vertically at the same time.The results are as follows: the damage pattern showed that the crack expanded from the top and the bottom of the column to the middle as the loading displacement increased.When the drift angle was less than 1/50,the columns with the longitudinal rebars continuous and discontinuous at the intersections have little difference in their bearing capacity and deformation capacity,and both of them had good bearing capacity and ductility.When the drift angle exceeded 1/50,distributed horizontal cracks appeared from the top of the column to the bottom.The bearing capacity of the columns with the longitudinal rebars discontinuous at the intersection was lower than those of the continuous columns,and their strength deteriorated more quickly.(3)A one-dimensional constitutive model and two-dimensional analysis model of concrete considering bond slip were developed,and numerical simulation of the model structures in the shaking table test was carried out using the developed constitutive model.Based on the quasi-static tests phenomena and mechanical properties of the columns of extra-large cooling towers,a one-dimensional concrete constitutive model considering bond slip was proposed.Based on the existing layered shell model and two-dimensional reinforced concrete model FSAM in OpenSees,the one-dimensional constitutive model considering bond-slip effect was extended to two-dimensional,and the numerical analysis model of two-dimensional reinforced concrete bond-slip effect was developed.A simulation method for reinforced concrete beams,columns,shear walls and shells considering bond-slip effect was proposed.The effectiveness of the above models was verified by the quasi-static tests on columns and shear walls.The developed constitutive model was used to simulate the isolated and non-isolated models of the extra-large cooling tower in the shaking table tests,and the reliability of the numerical simulation models used for large-scale structural analyses was verified.