Hysteretic behavior of high strength bolted joints of steel frame beams and columns

Steel frame bolt connection hysteretic performance Ministry of Science and Technology research project ( 012085) Hunan Provincial Department of Education funded project test overview test piece design and production node test piece has 3 groups, a total of 7 pieces, all the columns and columns are used 200 200 12 12. The beam-column stiffeners of all nodes are t=12mm, and the horizontal stiffeners of the column node are located at the corresponding positions of the beam flanges. Angle steel is made of Q235 steel. All bolts are made of 1019 M20 friction type high-strength bolts with a pre-tightening force of 155kN. The surface of the test piece that is in contact with the bolt before the bolt is installed is sandblasted. The thickness of the top of the column and the bottom of the column are 35mm, and the test piece has detailed dimensions.

Test piece connector size test piece number connection type steel (angle steel) specification (mm) split T-shaped steel connection top bottom angle steel web double angle steel connection top and bottom angle steel connection test device test reaction frame is anchored by four 50mm anchor bolts On the concrete floor of the laboratory, the hydraulic jack is connected with the U-shaped clamp attached to the reaction frame through a shaft with a diameter of 50 mm, which can be slightly rotated. The clamps made of four 32mm diameter screws and two splints are connected to the beam end, and the other end is connected with the jack. The loading device and instrument arrangement are shown in Figure 1.

The loading sequence and mode are based on the 5th seismic test method of the building (JGJ101). The quasi-static test scheme is applied to the beam-column joints to apply a low-cycle horizontal load. The horizontal load is applied at the beam end. Before yielding, load is controlled step by step by load control. The initial load is about 20 of the ultimate load of the structure. The load increase of each stage is about 20 of the total load. When it is close to the yield load, each stage is increased by about 10, and each stage is cycled. For 2 weeks, the horizontal displacement of the beam is used to control the specimen load after the yield is yielded. The displacement step is the yield displacement, and each stage is also cycled for 2 weeks until the displacement is too large or the specimen is broken. The yield displacement can be determined by the following two methods: First, the yield strain of the steel used in a section is the basis of the apparent inflection point of the P curve. Taking into account the specific circumstances of the test, the second method is used to determine the yield displacement of the structure. The failure of the connection is based on the looseness of the bolt or the apparent yield of the joined angle or the excessive corner of the joint.

The arrangement and measurement contents of the instrument are shown in Figure 1(b). The displacement meter (electromechanical dial indicator 1) is mounted on the flange of the beam and 450 mm from the upper flange of the column to measure the lateral displacement of the beam relative to the column. Table 1 is very close to the node, so the deflection of the beam is neglected, which is approximately equal to the reading of the electromechanical dial meter 1 minus the axial slip of the column measured by the dialect 2, and P450 is the relative angle of the beam and column. The H-pull pressure sensor is connected to the displacement meter together with the XY function recorder. The P hysteresis curve is directly drawn. Because of the linear relationship between P and M in the elastic range, the MH hysteresis of the connected node can be obtained by calculation and conversion. curve.

The dialects 2, 3, 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 top of the column when repeated loads are applied. The sub-table 5 is mounted on the web of the beam, and the plane of the main measuring beam is moved outward.

Test results Test results, where R is the initial rotational stiffness of the joint, which is the joint bending moment at the end of the test, H is the node rotation angle at the time of yielding, and M is the ductility curve at the end of the test. The L curve and the skeleton curve are shown in Fig. 2, 3.

Test basic conditions Test piece Note: The determination of the yield displacement is based on the obvious inflection point of the P curve.

The test results show that the plastic deformation ability of the high-strength bolt connection joint is much better than that of the welded or bolted joint. The limit rotation angle is greater than the 0103 rad required by the US FEMA. At the end of the test, the joint angle steel (T-shaped steel) at the flange is all compared. Large plastic deformation, and the column flange has almost no buckling. Therefore, most of the energy absorbed by the joint is dissipated through the T-connected angle steel, and the column flange is hardly involved in energy dissipation. The tensile properties of the seven specimens were better and the ductility coefficients were exceeded. 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 of the 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 Select td, t is the thickness of the split T-shaped steel flange, and d is the bolt diameter.

The T-shaped steel connection is considered to be the most rigid semi-rigid connection. A large number of data at home and abroad show that if t U d, the T-shaped steel connection can be regarded as a rigid connection, otherwise the T-steel connection has a large dispersion of stiffness, which is difficult to achieve rigidity. The stiffness requirements of the connection. The joint bending moment of all the test pieces is less than the plastic bending moment M pb of the beam section. The main reason is that all the test pieces are typical semi-rigid connections, and are not designed according to the principle of weak members of the strong node, so the section in the test The T-shaped steel connection node cannot be regarded as a rigid connection. It can be concluded from the test that the difference between ductility and energy dissipation capacity of T-shaped steel joints is that the thickness of the T-shaped steel flange is different, the thickness of the test piece JD12 is large, and the R is larger than that of the test piece JD11, so the split T The thickness of the steel flange 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, the shearing force is supported by the web at the joint, but the test results and the domestic and foreign literatures show that the bending moment assumed by the web is quite large and should not be calculated. Ignore, therefore, in calculating the flexural capacity of the beam-column joints, the influence of the joint angle at the web must be considered and the influence of the web angle is different due to the difference in the thickness of the top and bottom angles. When the top and bottom angles are small, the influence The effect is large. When the top and bottom angle steel is 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.

(1) The end plate connection has good ductility and energy consumption. When the corners of the joints exceed 0103rad, the end plate stiffeners can not only significantly improve the end plate stiffness, but also delay the weld between the beam flange and the end plate. The cracking effectively improves the bearing capacity and reduces the force.

(2) The test specimens have good ductility and ductility coefficients, which are suitable for the joint structure of earthquake-resistant areas.

(3) The thickness of the T-section steel flange is the main factor affecting the performance of the T-shaped steel joint. The increase of the thickness of the T-section flange is the most effective measure to improve the joint stiffness.

(4) For the bending capacity of the angle steel connection type, it is assumed in the common design method that the bending moment is all borne by the beam flange connecting angle steel, the shear force is supported by the web connection, but the test results and the domestic and foreign literature indicate that the web is assumed The bending moment is quite large and should not be neglected in the calculation. Therefore, the influence of the joint angle at the web must be considered when designing and calculating the bending moment bearing capacity of the beam-column joint.

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