Design Method And Mechanical Properties Of Stiffness Controllable Assembled Frame Joints

In practical engineering,ideal hinged joints and rigid joints do not exist.Semi-rigidity of joints is an inevitable problem in the research of assembled structures.Therefore,in the study of assembly structures,we can control the degree of semi-rigidity of joints,and study the calculation method and design theory considering semi-rigidity of joints.In this paper,a new type of stiffness controllable assembly joint is proposed.Through theoretical calculation,finite element simulation and full-scale experiments,the performance of this kind of joint is analyzed,and the performance of the frame using this kind of joint is analyzed.By controlling the semi-rigidity of the joints,the elastic deformation of the frame can be enlarged appropriately,so as to increase the ductility,plastic deformation performance and post-earthquake repairing ability of the structure.The main research contents and results are as follows:(1)Quantifying the degree of semi-rigidity of joints by using the theory of semi-rigid joints,and putting forward a quantitative method.It is considered that when the rotational stiffness R of the joint is in the range of 10000 kN.m/Rad to 15000 kN.m/Rad,the change of seismic action relative to the rotational stiffness R of the beam-end joint is obvious,and the semi-rigid effect should be considered.Seismic analysis of five-storey frame structures with semi-rigid joints is carried out and compared with ordinary frames.The natural vibration period,seismic load and seismic interlayer displacement are calculated.It can be seen that the natural vibration period of the frame structure with controllable stiffness joints is less than that of the ordinary frame,and its elastic lateral displacement is larger than that of the ordinary frame,which shows that the elastic stiffness of the structure is less than that of the ordinary frame.(2)According to a three-storey frame structure,a semi-rigid joint is designed to control the degree of semi-rigidity.The joint consists of four parts: tension-bending force plate,joint column end,joint beam end,middle pin bolt and bolt.The strength and stiffness of the column end,beam end and pin bolt are guaranteed,and the weak failure place is in the middle of the tension-bending force plate,which makes it fail before other parts.The rotational stiffness of the control joint is adjusted by changing the thickness of the tension-bending plate.A theoretical model is established to calculate the theoretical rotational stiffness of the joints under ideal conditions,and the relationship between the rotational stiffness and the thickness of the tension-bending plate is obtained.Using ANSYS finite element software,the refined models of three kinds of joints are established,and the stress and failure mechanism of the joints are analyzed.The bending moment and rotation angle curves and rotational stiffness of the joints are obtained by simulating the thickness of different plates.Compared with the theoretical results,the rotational stiffness of the joints calculated by finite element method is less than 20% of the theoretical results,which is due to the stress mode of the joints.(3)The solid fabrication of stiffness controllable frame joints is carried out,and their seismic performance is analyzed by quasi-static experiments.The experimental results are compared with the theoretical and finite element analysis results.By observing the phenomena of the experimental members,no cracks were found in the concrete beams and columns after the experiment.The deformation of the steel members at the end of the beams and columns was very small and no damage occurred.The failure occurred on the tensionbending plate.Through the analysis of a single hysteretic loop,it is found that the relative slip between the end of the beam-column steel joint and the tension-bending plate occurs at the beginning of loading,which results in the smaller initial stiffness.At the same time,due to the reinforcement effect of steel after yield,the experimental bearing capacity of the joint is higher than the theoretical value,which is close to 1.6 times of the theoretical value and 1.4 times of the finite element calculation value,which shows that the bearing capacity of the joint is good.(4)A three-story frame structure and a ten-story frame structure are simulated and analyzed by Etabs software.The seismic performance of the frame with controllable stiffness joints is analyzed and compared with that of ordinary concrete structures.It is found that the lateral displacement of stiffness controllable frame under low seismic intensity is larger than that of ordinary frame,which indicates that its elastic deformation stiffness is smaller,but the lateral displacement of stiffness controllable frame under high seismic intensity is smaller than that of ordinary frame,which indicates that the structural performance is better when the structure enters plastic deformation.Therefore,it can be concluded that the stiffness controllable structure has certain advantages when it bears large lateral loads under high earthquake.(5)By summarizing the performance of stiffness-controllable joints,the advantages and disadvantages of stiffness-controllable joints are analyzed,and the shortcomings are found,and the improvement methods are put forward.For example,the accuracy of component manufacturing and the improvement scheme,the initial slip of the joint and the improvement of the roughness of the contact surface of the tension-bending plate.The assembled stiffness controllable frame system is established,which is divided into transverse connection and vertical connection.By establishing some three-storey foundation frames,the design of expandable stiffness controllable frames can be carried out.