The instrument layout and measurement contents are shown in 1(b). The displacement meter (electromechanical dial indicator 1) is mounted on the beam flange and 450mm from the upper flange of the column to measure the lateral displacement Δ of the beam relative to the column. Table 1 is very close to the node, so the deflection of the beam is neglected. The approximate Δ is equal to the reading of the electromechanical dialym 1 minus the axial slip of the column measured by the dialect 2, and ΔΠ450 is the relative of the beam and the column. The rotation angle θr, the tension pressure sensor and the displacement meter are connected to the X2Y function recorder, and directly draw the P2Δ hysteresis curve; since P and M, Δ and θr are approximately linear in the elastic range, it can be obtained by calculation and conversion. The M2θr hysteresis curve of the connected node.
The dial gauges 2, 3, and 4 are installed on the column web. The dial gauge 2 mainly measures the axial slip of the column. The dial gauges 3 and 4 mainly measure the tilt of the column top when repeated loads are applied. The dial indicator 5 is mounted on the web of the beam, and the plane of the main measuring beam is moved outward.
The test results are shown in Table 2. In the table, R0 is the initial rotational stiffness of the joint, Mmax is the joint bending moment at the end of the test, θr, y is the node rotation angle at the time of yield, θr, u is the node rotation angle at the end of the test, and Mpb is the beam cross section. Plastic bending moment, μ test results analysis Compared with welded or bolted joints, the high-strength bolt joints have much better plastic deformation ability, and the limit rotation angle is greater than the 0103rad required by the US FEMA. At the end of the test, the joint angle steel (T-shaped steel) at the flange has all the large plastic deformation, and the column flange has almost no buckling. Therefore, most of the energy absorbed by the joint is dissipated by the T-connected angle steel. The edge is almost not involved in energy dissipation.
The tensile properties of the seven specimens were better and the ductility coefficients exceeded 31. It can be seen from the hysteresis curve that in the later stage of loading, as the deformation (curvature or displacement) increases, the slope of the tangent to the 2-node hysteresis curve decreases continuously, that is, the tangent stiffness decreases continuously, showing significant stiffness degradation. . The initial rotational stiffness of the split T-steel joint is greater than the initial rotational stiffness of the double-angle joint of the top-bottom steel web, which in turn is larger than the top-bottom angle.
When the stiffness of the split T-shaped steel flange is large, the initial rotational rigidity of the joint is large, which can ensure that the joint does not break before the plastic joint is formed. In order to obtain a large joint stiffness, the column flange plate must be thickened, and the T-section steel must be selected according to the relative relationship between the T-section steel stiffness and the bolt diameter. The thickness of the plate should be determined according to the principle of equal stiffness, that is, try to press tT≈d is chosen, tT is the thickness of the split T-shaped steel flange, and d is the bolt diameter.
The T-connection is considered to be the most rigid semi-rigid connection. A large number of data at home and abroad show that if tT≈d, the T-shaped steel connection can be regarded as a rigid connection; otherwise, the T-shaped steel connection has a large dispersion of stiffness, which is difficult to achieve. Stiffness requirements for rigid connections. The joint bending moment of all the test pieces is less than the plastic bending moment Mpb of the beam section. The main reason is that all the test pieces are typical semi-rigid connections, and they are not designed according to the principle of “strong node weak membersâ€, so the split in the test. T-steel connection nodes cannot be considered rigid connections. It can be concluded from the test that the T-shaped steel joints have strong ductility and energy consumption; the difference between the nodes JD121 and JD12 is that the thickness of the T-shaped steel flange is different, the thickness of the test piece JD12 is large, and the R0 and Mmax are larger than the test piece JD121, so The split T-section steel flange thickness is the main factor affecting the performance of the split T-steel connection joint.
The bending capacity of the two types of angle steel joints is significantly different, mainly because the joint angle at the web limits the rotation of the web, thereby increasing the bearing capacity of the joint. In the commonly used design method, it is assumed that the bending moment is all borne by the beam flange connecting angle steel, and the shearing force is taken by the web connection; but the test results and domestic and foreign literatures show that the bending moment assumed by the web is quite large and should not be calculated. Neglected, so in the calculation of the bending capacity of the beam-column joints must consider the influence of the angle of the joint at the web; and due to the difference in the thickness of the top and bottom angles, the degree of influence of the web angle is also different, when the top and bottom angles are small The effect of the impact is large. When the top and bottom angle steels are relatively thick, the effect is reduced.
Therefore, in the seismic building area to build steel structures, beam-column joints should be preferred to use semi-rigid nodes, because of the strong energy consumption and good ductility of such nodes. The semi-rigid connection steel frame has a large lateral displacement, and the most effective measure for limiting the lateral displacement of the T-shaped steel connection semi-rigid connection steel frame is to increase the thickness of the split T-shaped steel flange. For the bending capacity of angle steel joints, the influence of the joint angle at the web must be considered when designing and calculating the bending moment bearing capacity of the beam-colum joint.
Conclusions (1) The end plate connection has good ductility and energy dissipation capacity, and the corners of the joints exceed 0103 rad. When the end plates are thin, the end plate stiffeners can not only significantly increase the end plate stiffness, but also delay the gap between the beam flange and the end plate. The cracking of the weld seam effectively improves the bearing capacity and reduces the coercive force. (2) The test specimens have good ductility and the ductility coefficient exceeds 311, which is suitable for the joint structure of earthquake-resistant areas.
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