The loading design considers that a certain axial force is beneficial to the force of the column. Therefore, the axial force is not applied to the column, and the low-cycle repeated cyclic load is applied to the detailed description of the beam end node only by the MTS electro-hydraulic servo system. In order to prevent the overall instability of the steel beam, lateral support is provided at the end of the cantilever beam.
The measurement design places the displacement sensor on the beam end and measures the actual displacement of the beam end. Displacement sensors are placed at the center of the lower flange of the steel beam 100 mm and 250 mm from the cylinder to measure the actual displacement of the two points. A displacement sensor is arranged in the core region of the node for measuring the shear deformation of the core region of the node.
A pre-stress of 225 kN is applied to the high-strength bolt by the force-increasing wrench, and the construction pre-stress is increased by 5% in view of the loss of the pre-stress. When the corner reaches 010075rad, the steel beam begins to enter the yielding state. When the beam end is pulled for the first time to reach-0101rad, the column begins to show a curved crack. When the beam end pressure angle reaches 0101 rad for the second time, the first oblique crack begins to appear in the node area. When the corner reaches 01015 rad for the first time, the end plate of the tension zone begins to detach from the surface of the column, and in the subsequent cyclic loading, the gap between the end plate and the column surface gradually increases.
When the corner is -01045rad, the two bolts in the next row are simultaneously broken, the bearing capacity drops rapidly, and the test is stopped. Bolt breakage.
Before the test piece JD02 test piece JD02, a hydraulic torque wrench was used to apply a pre-stress of 355kN to the high-strength bolt, and the construction pre-stress was also increased by 5%. When the corner reaches 010075rad, the steel beam begins to yield. When the corner reaches 0103 rad, the end plate of the pull zone begins to open with the surface of the column. When the corner reaches 0105 rad for the first time, the bearing capacity of the node reaches the peak point, and the bearing capacity gradually decreases during the subsequent loading process. When the corner is 0106 rad for the first time, the bearing capacity of the node is reduced by 18%, and the test is stopped. Due to the high rigidity of the steel beam, the steel beam only showed slight buckling during the whole test.
The pre-stress applied to the high-strength bolt by the test piece JD03 test piece JD03 is the same as that of the test piece JD02. In addition, considering that the steel beam has a strong energy absorbing capacity, in order to allow the plastic hinge to occur on the steel beam, the steel beam is weakened by dog ​​bone <3>.
In the test, when the corner reached 010075rad, the steel beam began to yield. When the corner reaches 0103 rad, the end plate of the pull zone begins to open with the surface of the column. After the cycle with a corner of 0104 rad is completed, the bearing capacity of the node continues to rise. In the first cycle of the corner of 0105 rad, when the lower flange of the steel beam is pulled, the two bolts in the next row are broken and the test is suspended. At this point it can be observed that the weakened zone has a more pronounced yield and slight buckling, as shown.
Test analysis can be seen from the above, the test piece JD01 has good ductility and energy consumption, and has high bearing capacity. Due to the thickening of the end plate and the increase of the bolt diameter, the initial rotational rigidity of the joint of JD02 is greatly improved, and the bearing capacity and ductility of the displacement hysteresis curve are higher than that of the test piece JD01. The test piece JD03 has the most hysteresis curve due to the formation of the beam hinge failure. In addition, due to the weakening of the steel beam flange, the initial rotational stiffness of the joint is reduced, but the decline is not large, which is consistent with the analysis of <3>.
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