Study On Mechanical Properties Of Concrete Filled Circular Steel Tube-steel Castellated Beam Joint With Inner Stiffening Ring

Concrete filled steel tube is applied in civil engineering more and more widely for its high load-bearing capacity,good plasticity,high toughness and high ductility etc.Concrete filled circular steel tube-steel beam joint with inner stiffening rings(CFST-SBJWISR)is paid much attention for its clear force transmission path and good architectural effect.Steel castellated beam is also used more widely in civil engineering,due to less steel consumption,being convenient in construction and good seismic performance.But until now,there is no scholars carrying out concrete filled circular steel tube-steel castellated beam joint with inner stiffening rings(CFST-SCBJWISR).Therefore,the mechanical behavior of this type of joint under low reversed cyclic load is studied with the method of finite element simulation.First,the load-bearing process of an hollow circular steel tube-steel beam joint with inner stiffening rings and an concrete filled circular(rectangular)steel tube-steel beam joint with inner stiffening rings of the existent experiment are simulated.The result of simulation is compared with the experiment result,which shows they have good agreement with each other and the verified of the experiment is verified.Then,the load-bearing process of a CFST-SBJWISR and a CFST-SCBJWISR of the same size under low reversed cyclic loading process are simulated.By comparing their load-displacement hysteresis curves,skeleton curves,ductility and energy dissipation capacity,it can be seen that,the CFST-SCBJWISR has good seismic performance and it is easy to satisfy the “strong column weak beam” yield mechanism,and this type of joint has good engineering application value.The following parameters of CFST-SCBJWISR are changed,including the width and thickness of the rings,axial compression ratio,concrete strength,steel ratio,steel yield strength,beam to column linear stiffness ratio,hole spacing,opening rate and the distance between the first hole center and the column wall.There are 33 different joints that are designed with the different parameters.The load-bearing process of them are simulated under low reversed cyclic loading with the above finite element simulation method.And the corresponding load-displacement hysteresis curves,skeleton curves,ductility coefficient,energy dissipation coefficient and equivalent viscous damping coefficient are also calculated.The results show that,the load-displacement hysteresis curves of these joints are full and there is no obvious stiffness degradation;the displacement ductility coefficient,the energy dissipation coefficient and the equivalent viscous damping coefficient are high.It's further illustrated that the joint has good seismic performance.Based on the above results,the paper studied how different factors influences the load-displacement skeleton curve and the bending moment-corner skeleton curves.The results show that,the axial compression ratio,the concrete strength and the distance between the first hole center and the column wall have almost no influence on bearing capacity and ductility;the ring width and ring thickness of the joints have some effects on the skeleton curves;the steel yield strength,the steel ratio,the beam to column linear stiffness ratio,the hole spacing and the opening rate have great influence on the skeleton curves.The corresponding simplified equationsare regressed for calculating the flexural bearing capacity,the ultimate flexural bearing capacity and initial stiffness of this kind of joint.The accuracy of the simplified calculation formula is verified by the new simulation results.