Punching shear capacity of unbonded post-tensioned slab - Concrete filled steel tube column joints with innovative connections: Experiment and A new prediction model

Abstract

The punching shear behaviour of reinforced concrete (RC) flat slab - concrete-filled steel tube (CFT) column joints/connections has been diversely investigated in many studies. However, there have been no studies in the literature investigating the punching shear response of the joint made of unbonded post-tensioned concrete (UPC) slabs. This paper investigates experimentally the punching shear resistance and deformation capacity of the UPC slab - CFT column joints using proposed innovative connections. The experimental program was performed on six large-scale specimens, including three connections of UPC slab - CFT column, two connections of RC slab - CFT column and one conventional connection of UPC slab - RC column (control specimen). The test results showed that the UPC slab – CFT column specimens using the proposed innovative connections had higher punching shear resistance (up to 10%), ultimate deformation (up to 39%) and energy absorption capacity (up to 25%) compared to the control UPC slab - RC column specimen. The stiffness in the elastic stage before concrete cracking of the UPC slab – CFT column specimen was slightly larger than that of the control UPC slab - RC column specimen; however, it decreased rapidly in the post-cracking stage and was smaller than that of the control specimen by 13–28%. Changing the shape of the bearing plate from one annular plate to four discrete rectangular plates did not significantly affect the punching shear resistance of the flat slab–column joints but significantly increased the deformation capacity of the joints (by approximately 19%). The paper also proposes semi-empirical formulas to predict the punching shear resistance of RC/UPC slab - CFT column connections. The verification with the experimental data obtained from this study and other previous studies showed that the proposed formulas predicted the punching shear resistance of RC/UPC slab - CFT column connections close to the experimental data and had acceptable reliability.