Experimental study on mechanical properties of large-scale and semi-embedded concrete-filled steel tubular column base in Shenzhen Gangxia North comprehensive transportation hub
Shenzhen Gangxia North comprehensive transportation hub is in the downtown where available underground space is insufficient.The hub has a huge scale and complex loading conditions,and its core interchange area has a column-free super-large-span atrium of 51.2m×48.0m.To solve the problem of insufficient column base depth caused by the site conditions,based on the existing research results and engineering practice experience,a semi-embedded concrete-filled steel tubular column base joint was proposed and designed based on Shenzhen Gangxia North comprehensive transportation hub.To verify the reliability of the joint,the mechanical behavior of the semi-embedded column base under the combined action of axial force,shear force and bending moment was investigated through a 1/5 scale model test coupled with numerical analysis.The stress distribution law inside the column base was analyzed,and the working mechanism was revealed when the annular plates and studs were installed as shear connectors simultaneously.The analysis results show that under the design loads,the axial force of CFST column is mainly transferred through the annular plates and the bottom plate of CFST column,and the bending moment is mainly transferred through the steel tube sidewall pressure;the annular plates can obtain higher force transfer efficiency when embedded shallower,but the concrete underneath is prone to stress concentration;the studs on the steel tube sidewall can provide good shear resistance within the embedded depth.The piles below the pile cap are arranged reasonably.Under the design loads,the pile cap does not tend to occur punching shear damage,and the whole joint is in elastic working state.Under 1.2 times design loads,there is no evident degradation of the joint stiffness,no crushing or spalling of the joint concrete,no visible crack development on the surface,and the steel stress at each key position is lower than the material strength.The semi-embedded column base with annular plates and studs as shear connectors can achieve reliable embedding of the CFST column,and the proposed scheme of semi-embedded concrete-filled steel tubular column base reinforced by annular plates is feasible and meet the structural requirements.
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