Research On The Axial Behavior Of Circular CFT With Ribs

Concrete filled Tubes(CFT)are widely used in high rise buildings and skyscrapers,due to its excellent performance under axial and seismic loading.In recent years,CFT columns' diameter are expanded and structural measures are rearranged,with the escalation and complexity of building structures.Therefore several problems are brought up related to CFT structures.We focused on the axial behavior of circular CFT ribs in this dissertation,referring to the structural design of Haikou Tower.In this dissertation,12 circular CFT columns specimens are designed and seven of them are tested under axial load.The main variable parameters are vertical ribs,horizontal ribs,stirrup reinforcement ratio,with the aim to study on their effects on load capacity and failure mode.The result of the test indicates: all the specimens end up in shear failure,shear slip lines develop obviously throughout the specimens;vertical ribs can improve the axial load capacity of circular CFTs;horizontal ribs can improve both the axial load capacity and the ductility of circular CFTs,slower capacity decreasing;the application of headed studs and the change of stirrup reinforcement ratio show little influence on axial load capacity;the strength of concrete has a very direct effect on the capacity of CFTs,the higher the strength of concrete is,the more load CFTs can bear;steel yields before specimens reach maximum load.A little adjustments are introduced into formulas based on the unified theory and the ultimate equilibrium theory,in order to be more suitable for circular CFTs with ribs: the strength of vertical ribs and rebar is taken into account,the confining effect of horizontal ribs are considered in the confining factor ?.Errors between computational results and experimental results are less than 5%.The nonlinear analysis of tested specimens were carried out with the help of Abaqus,the computational outcome of capacity loads and load-displacement curve comply with experimental results.Parameter study was also performed,and it indicates that ribs have a direct effect on promoting load capacities of circular CFTs,the horizontal ribs can also improve the ductility performance while the vertical ribs cannot;increasing the steel ratio can effectively promote the load capacity and the ductility performance of CFTs;increasing the yield strength of steel can promote the confining effect,therefore the load capacity and the ductility performance are improved;increasing the compressive strength of concrete can effectively improve load capacity of CFTs,but the ductility performance will deviate.