Study On Dynamic Response Of Gravity Dams With Different Upstream And Downstream Face Under Earthquake

With the rapid development of China’s economy,the demand for energy is increasing.Due to the abundant hydraulic resources in the western region,in order to make good use of these hydraulic resources,China is carrying out the "western development" and "west to East power transmission" projects.Therefore,a number of high dams will be built in the western region in the future.The construction of dams must consider extreme natural disasters,especially in strong areas The structural safety of hydropower project under earthquake.When an earthquake occurs,the reservoir water and the upper surface of the dam will interact to form the seismic dynamic water pressure on the surface of the dam,which will cause the dam stress and deformation.If the seismic dynamic water pressure is too large,it will affect the safe operation of the dam.Therefore,the distribution of seismic dynamic water pressure is the key to the study.Under other conditions,the distribution of seismic dynamic water pressure is affected by the shape of upstream surface.In the current research,the upstream face of dam is generally regarded as a single shape plane,and the differences caused by different shapes are ignored.For example,the upstream face of concrete gravity dam is regarded as a vertical plane,and the actual engineering shape is not considered,so the pressure result obtained has a large deviation.In addition,the slope and shape of the downstream face of the dam will also affect the rigidity of the dam,thus affecting the stress and deformation of the dam body,and ultimately affecting the overall safety of the structure.This paper is supported by NSFC.In order to deeply discuss the law of seismic dynamic water pressure change and dam structure safety caused by dam slope change in upstream and downstream face of the dam,concrete dam is selected as the research object(compared with earth rock dam,the material rigidity of gravity dam is much greater).By studying the distribution of seismic dynamic water pressure of different dam slope gravity dam and its impact on dam safety,different schemes are compared and selected Find out the reasonable shape of upstream and downstream surfaces.This topic not only has the theoretical research value,but also has the important engineering practical value,which can provide the basis for similar dam design in the future.In this paper,quasi-static method and mode decomposition response spectrum method are used to study the dynamic characteristics and seismic safety of concrete gravity dams with different shapes under high seismic intensity by changing the upstream and downstream face of the dam.The main research work is as follows:(1)Through the modal analysis of gravity dam,the natural frequencies of empty reservoir,normal water level and check flood level are calculated respectively,and the natural vibration period and structural mode are obtained,and the natural vibration characteristics of dam body are analyzed.(2)In this paper,a typical concrete gravity dam is taken as the research object.The pseudo-static method and vibration mode decomposition response spectrum method are used to continuously change the dam slope of the upstream face of the gravity dam under three water level conditions: dead water level,normal water level and check flood level.The stress,strain characteristics and change rules of the dam body at the dam heel,upstream slope break and dam toe,as well as the parts where the stress concentration occurs are obtained By comparing the two methods,the optimal height of upstream slope break point and the weak position of concrete gravity dam are obtained.(3)The response spectrum method is used to continuously change the downstream face and slope of the dam body at the optimal upstream face slope breaking point height,analyze the stress and strain characteristics and change rules of the dam body at the dam heel,downstream slope breaking point and dam toe position at this time,obtain the optimal downstream face slope breaking point height of the dam body,confirm the mechanical weak parts of the concrete gravity dam,and put forward the corresponding resistance to these weak parts Earthquake measures.(4)Combined with the engineering examples,the upstream and downstream face slopes of the dam body are constantly changed,and the mechanical properties of each part of the dam body are calculated by using the mode decomposition response spectrum method to verify the optimal upstream and downstream slope breaking point height.Due to the differences in size,material,foundation and load of each dam,the universality of the research results is not high,but it provides a good reference value for the optimal design of concrete dam.Because the dynamic response of concrete gravity dam under strong earthquake is very complex,this paper has made some simplification in the analysis,and there are still some problems in the dynamic analysis to be further discussed and studied.