Experimental study on punching shear performance of embedded special-shaped CFST column base

The special-shaped concrete filled steel tube (SCFST) column has been widely applied due to its high load capacity, large bending stiffness and excellent architectural effect. However, the researches on the embedded special-shaped CFST column base (SCFST-CB) are quite inadequate, and the shape and initiation position of the shear failure surface of the SCFST-CB are still questionable. To fulfill the gap and obtain the shear principle of the SCFST-CB, five embedded SCFST-CBs were tested with the parameters of the installing of headed studs, the cross-section shapes and the dimension of CFST column. It was shown that installing headed studs would move up the initiation point of the shear failure surface and thereby increase the punching shear capacity and initial stiffness of the embedded SCFST-CBs. The cross-sectional shape of the SCFST column would affect the shape of the shear failure pyramid, while had negligible effect on the shear capacity and initial stiffness of the SCFST-CBs. Increasing the column dimension could significantly increase the punching shear capacity of the SCFST-CB. Bonding and headed studs could help transfer the axial load and the top row of headed studs took a much greater shear force than the bottom rows of headed studs. Neglecting the contributions of bonding and headed studs would make the calculation of the shear resistance by the current specifications too conservative. Finally, a modified method for calculating the punching shear capacity was proposed, taking into account the influence of the bond and headed studs. The predicted results fitted well with the experimental results.