Experimental And Theoretical Research On Reduced Beam Section Connections Of Steel Frame

Reduced beam section (RBS) connection of steel frame is one of the typical forms to move plastic hinge outward from the beam and column interface. By trimming beam flanges, the plastic hinge will form away from the welds that have much fracture proneness due to stress concentration and welding sensitivity, reducing the possibility of brittle fracture of connections and improving the ductility of the structure with RBS connections. In this dissertation, experimental and theoretical research on RBS connections with radius cut has been done.Six specimens under cyclic load were tested to investigate their hysteretic behavior and ductility behavior. Five specimens with different trimming depths, trimming lengths and trimming distances from column surface were conducted to get the effect for failure mode, ultimate load, plastic rotation angles and ductility behavior. In addition, one specimen with full welded connection was tested to compare their cycle behaviors. The test results show that RBS connections have a better plastic deformation and capacity of consuming energy than common connections. Hysteretic curves of RBS connection were well-shaped with large-area hysteretic loops, however, Hysteretic curves of common connection were flat. The plastic rotation angles of the five RBS specimens exceeded 0.04rad and their ductility coefficient exceeded 4.0, meeting the requirement for plastic rotation angles of 0.03rad and ductility coefficient of 4.0. Analysis results show that specimens with RBS connection have better capacity of consuming energy, and they can produce plastic hinge in region of beam trimmed, alleviating the stress state greatly and reducing the possibility of brittle fracture from weld, so that the strong-joint and weak-member design philosophy can be realized.Specimens with RBS connection and common connection under cyclic load and static load were analyzed respectively in the finite element software ANSYS. The main content of the finite element analysis under cyclic load was that the six specimens that had been used in the test were analyzed by 3D non-linear finite element method. Influence of beam flanges reducing parameters on mechanical behaviors of RBS connection was discussed systematically. Influence of trimming depth, trimming length and trimming distance on failure mode, ultimate load, plastic rotation angles and hysteretic behavior was discussed, and the results were contrasted with the test. The main content of finite element analysis under static load was that 17 specimens with RBS connection and 1 specimen with common connection were analyzed in ANSYS with 3D non-linear finite element. Stress distribution in the beam and bearing capacity of the specimens with RBS connection were mainly analyzed, and the effectiveness on the external motion of plastic hinge was discussed. And influence of trimming depth, trimming length and trimming distance on formation of plastic hinge was discussed, moreover, the bearing capacity coefficient C_pr in the equation of RBS connection design was discussed and the suggestion value was proposed.