Study on the rigidity of reinforced concrete double-beam joints of concrete-filled steel tubular columns Liu Zhibin, Zhong Shantong (School of Civil Engineering, Harbin Institute of Technology, Harbin 150090, China). A project has adopted this form of node and has been experimentally studied. The test results show that the double beam joints are less rigid. In this paper, the rigidity of the double-beam joint is analyzed theoretically, and the general method of node stiffness discrimination is proposed. It is considered that the joint stiffness is related to the stiffness of the structure. According to this method, the rigidity of the double beam joint is evaluated, and it is pointed out that the double beam joint structure used in the current project cannot be used as a rigid node. The general method of 1 node stiffness discrimination node stiffness and node stiffness are two different concepts. Node stiffness refers to the ratio of the bending moment acting on the node to the node rotation angle, which is an absolute value; and the node stiffness refers to the node The degree of just-connected, that is, whether the node is just connected or hinged, is a relative concept. Points are divided into just-connected nodes, semi-rigid nodes, and articulated nodes. As shown, the bending moments - corners of each node! -) Curve, when it is above the dotted line 1, the node is just a node, when it is below the dotted line 2, the node is an articulated node, and when the line is between the dotted lines 1 and 2, the node is a semi-rigid node. The disadvantage of this method is that it is separated from the actual structure and the absolute stiffness of the nodes is discussed in isolation. Therefore, it is proposed that the stiffness of the joint should be analyzed in relation to the stiffness and construction of the surrounding components. Because the actual node cannot be absolutely rigid, it can be regarded as an elastic node, and the elastic node is compared with the pure rigid node to judge the rigidity of the node. The specific method is as follows: As shown, take two identical frames. In the figure, "1" and "2" are the line stiffness of the column and the beam respectively. The elastic node and the pure rigid node are placed in the two frames, respectively. The same load applied to the frame is transmitted to the bending moment on the node as shown, where! 1,! 2 and! %, like 4 are the bending moments from the beam end and the column end respectively, and the internal bending moment of the node is equal to! 1+! 2 or! %+! 4. The inner bending moments on the elastic nodes and the pure rigid joints are respectively expressed as the calculations of the 锾 and 锾, and the ratio of the bending moments on the two nodes =! /! As a research object, considering the influence of the beam-to-column stiffness ratio, the results can be obtained. In the figure, the abscissa % is the relative ratio of the node stiffness of the elastic node to the stiffness of the column, %! Test simple. 2 Load diagram test The load diagram is shown, the axial load is applied at the end of the column, and the concentrated load is applied at the beam end. The distribution of the shear force between the legs of the node area and the joint area under the beam end load are measured. See the results of the relative rotation angle of the beam and column. 2.3 Problems existing in the test The device itself is unreasonable. It is a statically fixed structure. The rigidity of the joint cannot be judged by the test. The angular deformation of the joint area of ​​the test process is too large, and the rigidity of the joint is poor. It is necessary to further consider whether it is a rigid node. In-depth study. 3 Double beam joint stiffness analysis The main problems involved in node stiffness are the transmission mode of the joint bending moment and the angular deformation of the joint area caused by the bending moment transmission. The bending moments and beam sections of the double beam joint nodes are as shown. Four ways of bending moment transmission of double-beam joint nodes are proposed. The fourth method is considered to be the most effective, that is, the local pressure between the middle beam section and the column wall of the joint zone, which is transmitted during the concrete elastic working stage. The bending moment is 94% of the total bending moment of the node. Since the pressure distribution of the station is more complicated, the following is assumed as follows: the compressive stress in the vertical direction! It is linearly distributed, and is distributed on both sides of the column in the upper and lower parts of the section 1-1 in the node area, as shown in the figure; horizontal direction, using the polar coordinate system shown, compressive stress! On each side of the column, distribute the stress value at any point within the range of eve e! =2!213/, where! . It is the maximum stress value; the adhesion between the concrete of the beam section and the wall of the column is not considered. The compressive stress level distribution of the vertical compressive stress is calculated according to the distribution of the local pressure, and the angular deformation of the joint zone can be calculated. When the bending moment of the node acts on the side of the node, the angular deformation is different according to the boundary conditions on both sides of the node area. The specific calculation process is as follows: J loading side is unloaded side is the above two: E, (, a is a node The elastic modulus, shear modulus and Poisson's ratio of the beam section; D, h is the diameter of the column, and the height of the joint zone beam is 71994-2015 ChinaAcademicJournal; !" is the length of the beam section of the joint zone, equal to the diameter of the pillar plus 2 times the beam width, such as It is shown in the figure; "/, /% is the bending stiffness and torsional stiffness of the beam section of the joint zone. The result is compared with the test result, as shown by 0, 11. It can be seen from the comparison results of 0 and 11, the calculation results are in good agreement with the experimental results, but there is already a large angular deformation in the node region, indicating that the node pressure between the beam section of the node zone and the wall of the column is used to transmit the node. The bending moment is more realistic. Since the above analysis is in the elastic range, it can be superimposed when there are loads at both ends of the node region. The stiffness of the double beam joint / can be expressed by the following formula for the double beam joint in the test, the ratio of the stiffness in the linear elastic phase to the column stiffness in the test) = 8.71, and the beam-to-column stiffness ratio in the test is *=0.966, From the calculation results, the rigidity of the double beam joint in the test can be analyzed. In the figure, the curve of *=1 can be taken, according to the abscissa)=8.71, and the corresponding ordinate value on the curve is +=0.774. That is to say, in this structure, the difference between the double beam node and the pure rigid joint has reached 22.6%. As a rigid node, it is obviously no longer suitable. In the elastoplastic phase, the stiffness of the node is degraded, and it cannot be regarded as a rigid node. The double beam joints in the actual structure, such as only the bobs in the direction of the main axis, can be given according to the stiffness of the joint given by equation 8), combined with the line stiffness of the beam and column in the structure, according to the result, the double beam joint in the structure The rigidity of the evaluation. 4 Conclusions From the above analysis, the following conclusions can be drawn: the node stiffness is a relative concept, and the discrimination should be made in the actual structure. According to the relative ratio of the stiffness of the joint to the line stiffness of the beam and column in the structure of the node, the connection can be obtained. Or the conclusion of the hinge, the absolute stiffness value of the joint is not perfect; the node of the node can only play the role of the shearing force of the joint, and has little effect on the transmission moment; 8. The torsion beam section and the column of the joint zone The local pressure between the pipe walls is the most important and effective way to transmit the bending moment of the joint; the stiffness of the double-beam joint is represented by the formula 8), and the relative ratio of the linear stiffness of the beam-column in the structure of the node can be judged. The rigidity of the beam joint. About SD DEXIANG: Carbon Crystal Heater,Infared Electric Heater,Carbon Crystal Infrared Panel Heaters,Far Infrared Carbon Crystal Panel Heater Shandong Dexiang Electrical Technology Co.,Ltd , https://www.heater-kerosene.com
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Study on rigidity of reinforced concrete double-beam joints of concrete filled steel tubular columns
Study on the rigidity of reinforced concrete double-beam joints of concrete-filled steel tubular columns Liu Zhibin, Zhong Shantong (School of Civil Engineering, Harbin Institute of Technology, Harbin 150090, China). A project has adopted this form of node and has been experimentally studied. The test results show that the double beam joints are less rigid.