| After the Northridge and Kobe earthquake,engineers generally carried out lots of experimental research and theoretical analysis of steel frame beam-column joints,and found that the seismic performance of joints can be changed by strengthening or weakening the structure.RBS(Reduced Beam Section)node belongs to a new type of post-northridge node,which can make the plastic hinge away from the connection.Based on the previous studies,this paper researches the seismic performance of RBS box strengthen-joint region connection for weak axis of I-section column and puts forward design countermeasures.It is divided into two parts: experimental study and finite element analysis.First,a full-scale test of cross side joint with RBS box strengthen-joint region under monotonic loading was carried out based on the proposed joint.Characteristics such as failure features,hysteresis curves,skeleton curves,stress strain of the main parts,energy dissipation coefficient,ductility coefficient,and stiffness degradation were analyzed.Second,the test was simulated by using ABAQUS,in order to to validate the finite element models.Third,33 models with various parametres of 3 series were built to analyze how the thickness,weakning parametres and the changes of beam-column linear stiffness ratio influence the behavior of joints.At last,two engineering joints RBS-1 and RBS-2 were analyzed to verify the rationality of design method and parametres value.The main contents include the following points:(1)The test results show that: specimen RBS can form plastic hinge at the weaken part of the beam end,and make the plastic hinge away from the connection,which meet the requirements of seismic design of ‘strong column and weak beam';The elastic shear deformation in joint region loading process is small,which indicates that the type of RBS node presents feature of ‘strong joint region'.The weld of skin plate corresponding to the left side beam and column stiffener cracked prematurely,caused the left side of the beam axis deviation 50 mm.And layer tearing phenomenon occurred in skin panel,thus Z direction steel is recommended to ensure the welding quality.In order to improve the aseismatic capacity of energy dissipation,ductility and rigidity degeneration,it is necessary to select the appropriate stiffness ratio of beam to column and ensure the welding quality in practical engineering.(2)The finite element analysis show that: the thickness of the skin panel has significant influence on the seismic performance of RBS new beam-column weak axis connections.So the thickness value of skin should be reasonable in practical engineering.The influence of different parameters on the has different influence on the stiffness of the beam and column,weakning parametres and beam-column linear stiffness ratio have different effects on bearing capacity,energy dissipation capacity and ductility of the new type RBS specimen.When using the proposed joint in the engineering design,the distance from starting point of weakened area to surface of skin plate is recommended as 55%~80% of beam flange width,the length of weaken area is recommended as 65%~90% of beam section height,the depth of weaken area is recommended as 20%~25% of beam flange width.The beam-column linear stiffness ratio should not be greater than 1.5.(3)The analysis of two engineering joints RBS-1 and RBS-2 shows that: the finite element analysis results verified the rationality of design method and parametres value mentioned above,and the new design method can be applied to practical engineering. |
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