| Concrete-filled double skin steel tube was formed by two different sizes steel tubular of concentric placement.and the cavity between the steel tubes was filled with concret.It has the virtues such as high bearing,capacity,better plasticity,convenient construction large,unfolding cross-section,light deadweight,fire resistance and better anti-seismic performance,etc.In the past,the research on Concrete-filled double skin steel tube was mainly about component.However,there are few studies on frame joints.Frame joint play a key role in the integrity and stability of structures especially in elastoplastic phase which subjected to seismic load.At present,the joints of concrete filled steel tubular columns and steel beam are widely used in engineering due to their short construction period,assembly and good aseismic performance.In this paper,the joints of concrete filled steel tubular columns and steel beam were studied.The method of steel tube stiffening in the joint area was adopted to avoid the trouble of connection between the inner tube and the beam and ensure the smooth transmission of the force.In addition,the finite element software ABAQUS was used to analyze the stiffening rib joint.The influence of stiffeners on the mechanical properties of joints was studied,and the type of stiffened joints was judged by stiffness.The main work listed as follows:(1)Selection of appropriate finite element models.The results of other people’s experiments were compared with those of the finite element analysis method adopted in this paper.The results indicated that the simulation results are in good agreement with the experimental results,which verifies the reliability of the finite element modeling method used in this paper.(2)Specimen design and finite element simulation.The finite element models with different stiffening rib lengths were designed according to the requirements of seismic design.The seismic performance of the specimens without ribs and with different lengths of ribs under low cyclic reciprocating loads was analyzed.Research result explained that stiffening of the inner steel tube can obviously increase the seismic performance of the joints.The skeleton curves of hysteretic curves of joints were compared with the load-displacement curves under monotonic loads.The basic coincidence of the two curves shows that monotonic load can be used to analyze the effect of stiffeners on the mechanical properties of joints.(3)Analysis of the effect of stiffeners on the mechanical properties of joints.In this paper,the mechanical properties of Stiffeners under different lengths and widths were studied.The study showed that the bearing capacity of joints increases with the length of stiffening ribs,but it does not increase when the length of stiffening ribs is greater than 0.75.Displacement ductility coefficient and displacement angle ductility coefficient increase with the increase of stiffening rib length when β is less than 1.The amplification of displacement ductility coefficient is smaller and smaller when β in the range of 0.5-1.Nevertheless,displacement ductility coefficient and displacement angle ductility coefficient tend to decrease when beta is more than 1,.The longer the rib length is,the stronger the flexural and shear capacity of the joints are.When the width coefficient of the stiffener k is less than 0.5,the ductility coefficient of the joint go up with the rise of the width of the stiffener.the growing rate of the ductility coefficient increasingly smaller when k within the range of 0.17-0.5.However,the displacement ductility coefficient decreases when k exceeds 0.5.The larger the stiffener width,the better the flexural and shear capacity of the joints.(4)Impact analysis of other parameters.Taking the length coefficient of stiffener(β=1)and width coefficient(k=0.5)as basic parameters.The effects of axial compression ratio,hollow ratio,steel beam strength,inner steel tube strength,outer steel tube strength and concrete strength on the mechanical properties of ribbed square-sleeved circular hollow sandwich concrete filled steel tubular column-steel beam joint were analyzed.(5)Analysis of force mechanism and judgment of stiffness type.Typical specimens were selected to analyze the mechanical mechanism of ribbed square-sleeved circular hollow sandwich concrete filled steel tubular column-steel beam joint.In the meanwhile,the influence of stiffener length and width on the mechanical mechanism of such joints was obtained.Besides,The stiffness types of joints were analyzed and judged.Moreover,a simplified formula for calculating the flexural stiffness of joints was proposed.The calculated results are agree well with with numerical results. |
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