| Concrete filled steel tubular column(CFSTC)is widely used in practical engineering with the advantages of high bearing capacity,good ductility,toughness and fire resistance.Steel castellated beam(SCB)have been vigorously generalized in the project with the advantages of saving steel,high rigidity and convenient pipeline layout.If they are connected,not only the advantages of each can be realized,but also the yield mechanism of "strong column and weak beam" is easier to achieve.At present,the reference on diaphragm-through type concrete-filled square steel tubular column-steel castellated beam(DTCFSTC-SCB)joint has not been found.Therefore,the study on mechanical properties and calculation method for designing of DTCFSTC-SCB is carried out in this paper.The finite element model of diaphragm-through type concrete-filled square steel tubular column-steel solid beam(DTCFSTC-SB)joint is established by using the finite element software ABAQUS,and its load-bearing process under low-cyclic repeated load is simulated and analyzed.Compared with the simulation results and the experiment results,the results show that both agree well.Meanwhile,it also shows that the finite element simulation method is reasonable.On this basis,a model of DTCFSTC-SCB joint with the same size of the DTCFSTC-SB joint is established according to the proportion of 1:1.By comparing the hysteresis curve,skeleton curve,ductility coefficient and capacity of energy dissipation of these two models under the low-cyclic repeated load,it can be seen that the DTCFSTC-SCB joint also has higher bearing capacity,good ductility and capacity of energy dissipation,and the yield mechanism of "strong column and weak beam"can be realized more easily.So it can be concluded that the DTCFSTC-SCB joint has feasibility in engineering application.By changing the factors such as the within and extended width of diaphragm,thickness of diaphragm,axial compression ratio,the strength of concrete,steel ratio,the yield strength of steel,the stiffness ratio of beam and column,the hole opening ratio,hole distance and the distance between first hole and the wall of the column,34 DTCFSTC-SCB joint are designed.The loading process of each joint under low-cyclic repeated loading are simulated by using finite element simulation method which mentioned above.At the same time,the corresponding hysteresis curves,skeleton curves,ductility coefficients and equivalent viscous damping coefficients are calculated from the above simulation.It can be seen from the calculation results:the hysteresis curve of these joint are relatively full and there is no obvious stiffness degradation;the displacement ductility coefficient is greater than 3.86;the energy dissipation coefficient is from 1.07 to 2.26 and the equivalent viscous damping coefficient is from 0.17 to 0.36.All these further explained that this type of joint has good seismic performance.Based on the above simulation results,the influence of factors on hysteresis curve skeleton curve is quantitatively analyzed.The results show that the extended width of the diaphragm,the thickness of the diaphragm,the yield strength of the steel and the stiffness ratio of the beam and the column are main factors which effects on skeleton curve,while other factors have little influence.According to the above moment-rotation skeleton curve of each joint,the flexural capacity,ultimate flexural capacity and initial stiffness of each joint are calculated.Based on the above calculated data,a simplified formula for the flexural capacity,ultimate flexural capacity and initial stiffness is regressed.Then,the accuracy of the simplified formula is verified by using new joints which are designed to be different from the above joints.The error between the finite element simulation results and the simplified calculation results is small.Therefore,it provides a theoretical basis for the engineering application and regulation of relevant specifications. |
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