Dynamic Model Tests Of High Concrete Gravity Dam With Longitudinal Joints

The safety performance of high concrete gravity dams under earthquake is a very concerned problem in engineering.For large volume dams,there are usually longitudinal joints in the dam body because of the large section size.Under the action of earthquake,the local tensile strength of the longitudinal joint of the high gravity dam is relatively low,which is easier to stretch and damage than the whole dam,thus threatening the integrity and seismic performance of the dam.In this paper,a concrete gravity dam with two longitudinal joints and a height of 185m has been built as the research object.Based on the similarity theory,the dynamic response of the elastic model and the dynamic failure model test were carried out by shaking table.The purpose of this study is to explore the influence of the existence of the longitudinal joints of gravity dams on the dynamic response including strain response,acceleration response and the dam crest displacement,as well as the crack position and fracture extension mode of the dynamic failure dam model in the plastic stage.The summary is as follows:(1)Three high concrete gravity dam model tests including a whole model,a longitudinal seams model and two longitudinal seams model are carried out in the shaking table test.The test results show that the existence of longitudinal joints greatly reduces the frequency of the dam and changes the distribution law of the strain response of the gravity dam.The maximum tensile strain of the integrated dam is located at the dam neck,however,when the longitudinal joint is set to the dam,the dam neck strain decreases,and the tensile strain at the bottom of the dam is the largest.The longitudinal joints accelerate the acceleration of the platform at the middle part of the downstream dam,but inhibit the amplification effect of the dam top.The top relative displacement of the single slit model is smaller than that of the integrated dam,while the displacement of the double slit dam is obviously larger than others.(2)In order to make the model test reliably simulate the whole process of the dynamic failure of the concrete dam in strong earthquakes,it is required that the strain ratio of the model material is as much as 1,and the stress-strain relation curve of the material should be in accordance with the prototype concrete as much as possible.In this paper,a particle mortar concrete is developed as a model material.The results of mechanical performance test show that the main physical properties of tensile strength,compressive strength and elastic modulus are similar to those of the prototype.According to the model similarity theory,the dynamic model test of the dam can be used to simulate the crack location,direction and the range of the crack under the strong earthquake.(3)Taking the developed particle mortar concrete as the model material,the shaking table dynamic failure model test was carried out for a high concrete gravity dam with two longitudinal joints.The results show that the cracking of the whole model of concrete gravity dam is different from that of the integrated dam,which is cracking from the head of the dam.The cracking of the dam with two longitudinal joints begins at the upper end of the longitudinal joint,and develops along the direction of the slope downward with the earthquake action.When the dam is cracked,the maximum strain value is measured above the slope of the downstream of the dam.(4)Based on the Abaqus,the numerical analysis of the prototype of the concrete gravity dam is carried out and compared with the dynamic model test failure mode.The results show that the two are in good agreement.Due to the limited test conditions,the static water pressure is not considered in the experiment.Therefore,the influence of the static water pressure on the dynamic response of the dam with longitudinal seams is discussed in the numerical simulation.The mode and range of tensile damage,the relative displacement at the top,and the distribution of main stress of the dam are discussed.(4)The numerical analysis of the two-dimensional prototype model of concrete gravity dam is carried out.In the numerical simulation,the influence of the static water pressure on the dynamic response of the dam with longitudinal seams is discussed,including tensile damage,the relative displacement of the top and the distribution of the maximum principal stress.The simulation results show that the hydrostatic pressure will significantly increase the maximum principal stress of the dam.The heel of the dam,and the upper and lower regions of longitudinal joints are in a high stress state.However,the opening of the longitudinal joint and the relative displacement of the dam crest will be reduced.