Research On The Mechanical Behavior Of Ellipsoidal Nodes Of Lattice Wind Tower With Concrete Filled Steel Tubular

At present,many kinds of universal wrapped joints have been designed for the assembly construction of lattice CFST wind power tower.However,through model test and finite element simulation research,it is found that the existing universal wrapped joints have many defects,such as insufficient spherical restraint,flexibility of joint plate and failure of resultant force to converge with tower columns,which are not conducive to the promotion and use of lattice concrete-filled steel tubular wind power tower.In view of this,based on the previous research of the subject team,this paper proposed an ellipsoidal bolted spherical joint,designed and manufactured four groups of scale model specimens and carries out static test.The mechanical behavior of such joint was further studied by combining with nonlinear finite element analysis.The specific research contents and conclusions were as follows:(1)The calculation model of CFST lattice wind power tower was established by SAP2000 structural design software,and the inner force of the tower was calculated as per the latest code load combination.Researches indicate that under the most unfavorable load condition,the maximum horizontal displacement of the tower top is about 349 mm,which is equivalent to 0.56% of the total height.The internal force of the tower web is positively correlated with the height of the tower.The diagonal web bears a maximum tensile force of 184 k N and a maximum pressure of 204 k N,which is located on the 5th and 16 th floors of the tower respectively.The inner force ratio of each layer is controlled between 1.01 and 1.09.The joint of the 16 th floor of the tower is the most disadvantageous joint position of the frame.(2)Based on the calculation results of internal forces of the tower in SAP2000,four groups of ellipsoidal bolt spherical joint scale specimens were processed by taking the most unfavorable position of the top node of the tower as the prototype reference of the specimen model and taking the wall thickness of the ball table and web bar as test parameters.The failure modes of ellipsoidal joints can be divided into three categories:tear failure of the welds between the cylinder body of the ball table and the bearing plate of the ball table,material failure of the ball table press plate and stress failure of high-strength bolt threads of the tension webs.(3)By analyzing the strain information collected in each measuring area,the influence of the change of ball table wall thickness and web bar wall thickness on the overall bearing capacity of joint and the distribution law of equivalent stress of each component was investigated.The finding indicated that the bearing capacity of specimens increases by 26% and 31% respectively when the thickness of web bar increases from 3.5mm to 5 mm,while the thickness of ball table increases from 6 mm to 10 mm and the bearing capacity of specimens increases by 4% and 13% respectively when the thickness of web bar is the same.Elastic and elastic-plastic stages of development of Web force-displacement relation curve of ellipsoidal joint specimens are longer,web deformation and bearing capacity are better,and stress distribution is more uniform.Under the action of horizontal web force,one side of tensioned web rod and ellipsoid are severely extruded,and stress concentration is obvious.Stress distribution on both sides of tension and compression is uneven,and stress extreme difference is large.(4)Finite element simulation analysis of such joints were carried out by combining SolidWorks and ABAQUS,and the applicability and reliability of this method are verified by comparing the test results,and the related parameters analysis were extended on this basis.The results showed that the overall stress level of core concrete in the tower column is low,and C30 strength concrete should be used in the subsequent study.Such joints should be designed according to the principle of "strong joint,weak member".The wall thickness of Web rod should not exceed 5mm,and the bearing plate should be welded on the top of the shell when the table is processed to avoid the neglect of the thickness of the bearing plate of the table leading to the reduction of the actual bare volume of the ball and the interference between the ball table pressure plate and the bolt sleeve of the web rod.It is reasonable to select the thickness of 9mm and the ball table pressure plate of 16 mm.