A study on seismic performance of semi-rigid connection in steel frame

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The connection type, which the steel element of the composite beam is welded directly to the steel flange of the rectangular hollow section (RHS) column without any diaphragms, was selected for an example of the semi-rigid composite joint.The composite beam-and-RHS column subassemblage specimens, whose connection strength are of the following three categories classified by the strength ratio of the semi-rigid connection to the composite beam member, that is (i) the yielding of the beam flange is expected in advance of the connection, (ii) the yielding of the beam flange is expected after the connection, and (iii) the failure of the connection is expected in advance of the yielding of the beam flange, were carried out. The hysteretic characteristic of the subassemblages is stable spindle type until the drift angle of 1/25 regardless of the difference of failure mode. And the relationship between the moment (jM) and local rotational angle of the connection (jrheta) is obtained for each connection.Three 2 bay-2 story unbraced steel frames consisted of the composite beams and RHS columns, whose beam-to-column connections without diaphragms are of the above three categories, were tested. The obtained load-drift angle relationship of each frame is stable spindle type with satisfactory deformation capacity regardless of the difference of failure mode. The effect of the semi-rigid behavior of the connection on the structural behaviors of the frames is analyzed by using the rotational spring model for the connection.In addition, as jM-jrheta relationships of this type connections can be analyzed precisely by the three dimensional elasto-plastic finite element method, the formulation of the jM-jrheta relationship of the connections is possible by accumulating the results of the case studies by the finite element analysis.