Research On The Factors Affecting The Bearing Capacity Of The Beam-column Joint With Upper Ring And Lower Inner Diaphrag

Concrete-filled flat steel tubular column refers to a rectangular concrete-filled steel tubular column with the height-width ratio of 2 ～ 4.Because the width of the section of the concrete-filled flat steel tubular column is equal to that of the wall,it can be hidden inside the wall,so as to save the use space and increase the aesthetic feeling of the building.However,due to the small section size of the concrete-filled flat steel tubular column,the use of internal partition joints will cause problems such as difficulty in concrete pouring and difficulty in meeting the requirements.At the same time,the outer ring plate joints are contrary to the original intention of hiding in the wall.Therefore,In order to find a joint form that can be hidden in the wall,meet the bearing capacity requirements and facilitate concrete pouring,this thesis puts forward a new type of beam-column joint-flat steel tube beam-column joint with upper ring and lower inner diaphragm,carries out ABAQUS finite element analysis on its mechanical properties under static load and reciprocating load,studies the influencing factors of bearing capacity of flat steel tube beam-column joint with upper ring and lower inner diaphragm,and puts forward some suggestions for practical engineering application of beam-column joint with upper ring and lower inner diaphragm.Firstly,according to the relevant domestic codes,the specimen size of flat steel tube beam-column joint with upper ring and lower inner diaphragm is designed,and the checking calculation in elastic stage is carried out.The checking results meet the requirements,which verify the feasibility of flat steel tube beam-column joint with upper ring and lower inner diaphragm.Secondly,ABAQUS finite element simulation is carried out for the beam-column joints of flat steel tube with upper ring and lower inner diaphragm,and static load and reciprocating load are applied to the joints,so as to clarify the force transfer mechanism and failure mechanism of the beam-column joints of flat steel tube with upper ring and lower inner diaphragm,and determine the mechanical performance indexes such as bearing capacity,ductility and energy dissipation capacity of the joints.The results of ABAQUS finite element simulation show that the failure of beam-column joints with upper ring and lower inner diaphragm is later than that of beam-column,which strongly proves that the design of beam-column joints with upper ring and lower inner diaphragm conforms to the principle of "strong joints and weak members".The hysteretic curve of the beam-column joint of flat steel tube with upper ring and lower inner diaphragm presents a full shuttle shape,and the skeleton curve is symmetrical about the origin shape,which shows that the beam-column joint of flat steel tube with upper ring and lower inner diaphragm has good seismic performance and energy dissipation capacity.Then,three sets of comparative specimens with different parameters,such as the thickness of the inner diaphragm,the width of the opening margin of the inner diaphragm and the opening of the inner diaphragm,are designed,and the numerical simulation is carried out by ABAQUS finite element software,and the mechanical properties of each specimen under static load and reciprocating load are studied,and the effects of the three sets of parameters on the mechanical properties,ductility,energy dissipation capacity and bearing capacity of the beam-column joints with the inner diaphragm under the upper ring are discussed.The analysis results show that if the thickness of the inner diaphragm is too small,it will seriously affect the stress and deformation of the joints.Increasing the thickness of the inner diaphragm can improve the bearing capacity and seismic performance of the flat steel tube beam-column joints under the upper ring and lower ring.However,when the thickness of the inner diaphragm is close to the thickness of the beam flange,it has little effect on the joint performance.It is suggested that the thickness of the inner diaphragm should not be too thin,and it is better to be greater than the thickness of the beam flange by 2mm;when the width of the weak axis of the inner diaphragm is small,the stiffness of the joint is weak.At this time,increasing the width of the weak axis of the inner diaphragm can significantly improve the bearing capacity and seismic performance of the joint.When the size of the flat steel tube column is160mm×400mm×14mm and the size of the H-beam is 400mm×150mm×8mm×13mm,after the width of the inner diaphragm reaches 25 mm,the bearing capacity will be continuously increased.It is suggested that the margin width of the partition in the node should not be less than 15mm;if the margin width of the inner diaphragm cannot be increased,the bearing capacity and seismic requirements of the joint can be achieved by thickening the inner diaphragm.