Study On The Seismic Performance Of Circular Concrete-Filled Steel Tubular Column To Steel Beam Joint With External Diaphragm

Concrete filled steel tubular (CFST) columns are being widely used in engineeringstructures in recent years. It is thus very important to thoroughly investigate theperformance of CFST column to beam joints, especially the joints with reinforcedconcrete (RC) slab. This paper evaluated the seismic performance of beam-columnjoints consisted of circular CFST column and steel beam with external diaphragm andRC slab through both experimental and numerical methods. The main research workand achievements are summarized as follows:1. Experiments are carried out on the composite joints with constant axial load onthe top of the column and reverse cyclic loading at the end of the beams. Theparameters include: the axial load ratio of CFST column; the beam to column strengthratio and the beam to column stiffness ratio. The influences of these parameters on thejoint cyclic behaviour as well as the failure modes were investigated. The resultsshowed that the load versus deflection curves were plump and stable strength andstiffness degradations were observed under cyclic loading. It is concluded that this kindof joints had a favorable hysteresis characteristic.2. Nonlinear finite element analysis (FEA) was conducted for the composite joints.The FEA model considered both geometrical and material nonlinearity, interaction andconnection between steel and concrete, residual stress and initial imperfection, etc.Damage indexes for both confined and common concrete under cyclic loading wereproposed based on the concept of "focal points method" from the stress-strainrelationship of confined and plain concrete. The accuracy of the FEA model wasverified by extensive experimental results, including results of structural member tests,joint tests from other researchers and joint test from the author.3. The failure modes, force transfer mechanism, force versus deformation relationsof the composite joints were analyzed by the FEA model. The failure modes of thejoints were categorised. The internal forces, stress and strain distribution at differentcharacteristic points on the force versus deformation relations were investigated. Acomprehensive parametric study was conducted. Influences of the parameters on thejoint behaviour were analyzed. The parameters included: the thickness and width of RCslab, the axial load ratio of panel zone, the beam to column strength and stiffness ratio, the properties of the external diaphragm and the panel zone, etc.4. A shear versus shear deformation hysteretic relation for the panel zone of thejoint was established based on the parametric analysis. A joint element model with thishysteretic relation implanted was proposed for joints in planar frame. It is concludedthat the proposed hysteretic relation and the joint element model had a favorableaccuracy when compared with the FEA and experimental results.