| Due to its superior mechanical properties,concrete-filled steel tube has been used more and more widely in building structures in recent years.The concrete-filled steel tubular column has the advantages of high bearing capacity,beautiful effect of beam-column connection and convenient furniture arrangement.Compared with special-shaped reinforced concrete columns,the bearing capacity of concrete-filled steel tubular columns with the same section size is stronger.Due to the lack of joint types of special-shaped concrete-filled steel tubular columns,a complete theoretical system has not been formed,which restricts the application of special-shaped concrete-filled steel tubular columns.Therefore,this paper proposes a cross-shaped concrete-filled steel tubular column and steel beam joint connected by side plates.The finite element software ABAQUS is used to conduct research on this joint.The main research contents are as follows:(1)Three kinds of cross-shaped joints with different linear stiffness ratios are designed.Type A is A model designed according to the design principle of "strong joint,weak member",and Type B and C are weak joint models,which are respectively used to study the bending and shear properties of new joints connected by side plates.The finite element software ABAQUS was used to build a fine numerical model,and the pseudo-static loading was carried out.The finite element results show that the A-type joints with side plates form plastic hinges at the flange of the steel beam at the end of the side plates,which belongs to beam hinge failure.In B-type joints with side plates,a plastic zone appears at the column Angle of the beam-column connection at first.With the increase of loading displacement,the plastic hinges gradually expand on the column wall and side plates.Finally,until the plastic hinges run through the entire section of the beam-column connection,the joints are damaged and the bearing capacity begins to decline.The failure mode of C-type joint is shear failure in the core area.(2)Parameter analysis is carried out for three types of joints A,B and C respectively.The influence of side plates and side plate length on A-type joints is considered.B-type joint parameters are whether there are side plates,axial compression ratio,side plate height and side plate thickness,respectively.Type C joint parameters are axial compression ratio and side plate thickness.The results show that for strong joints,the presence of side plates can make the plastic hinges move outwards and improve the ultimate bearing capacity and ductility of joints.The existence of side plates significantly improves the ultimate bearing capacity of B-type joints,and the ultimate bearing capacity increases with the increase of the height and thickness of side plates.With the increase of axial compression ratio,the ultimate bearing capacity of B-type joints decreases.With the increase of axial compression ratio and side plate height,the ultimate bearing capacity of C-type joint increases slightly.(3)Based on the yield line theory and B-joint finite element results,the yield mechanism of steel tube webs limb flanges was established,the strengthening coefficient of core concrete was proposed,and the ultimate tensile capacity of steel tube flanges on steel beam was calculated.According to the static balance method,the tensile force transmitted by the side plate is calculated.On this basis,the formula of ultimate flexural capacity of such joints is proposed.Based on the finite element results of C-type joints,the shear failure yield mechanism in the core area of the joints was established.By using the principle of concrete baroclinic bar and superposition method,and considering the contribution of flange to the shear resistance of the joints,the calculation formula of ultimate shear capacity of the joints was proposed.The formulas for calculating the flexural and shear capacity proposed in this paper are in good agreement with those calculated by finite element method.Therefore,the formula proposed in this paper can be used in practical engineering design after further modification.(4)On the basis of reasonably determining the material constitutive and mechanical properties after fire,the pseudo-static loading model of CFST column-I-beam joints connected by cross side slabs after fire was established,and the influence of heating time on the bearing capacity of the joints after fire was considered.The results show that,compared with the joints at room temperature,the ultimate bearing capacity of the joints at 30 min,60min and 90 min cooling to room temperature decreases by 14.88%,22.14%and 25.20%,respectively. |
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