Experimental investigation and confinement model of composite confined concrete using steel jacket and prestressed steel hoop

Abstract

This paper presents the results of an experimental study of the uniaxial compression behavior of circular section concrete columns confined by composite confinement (CC). The composite confinement includes prestressed steel hoops (PSH) active confinement and steel jackets (SJ) passive confinement. PSH can solve the problem of passive confinement stress lag, whereas SJ retains the prestressing well and prevents the PSH from penetrating the concrete or causing stress loss. The composite confined concrete specimens were tested with the variations of different initial prestress levels and steel hoop centerline spacing. Their behavior was compared with different types of confinement forms, including unconfined concrete (UC), active confined concrete (PSH confined concrete, PC), passive confined concrete (SJ confined concrete, SC). The results of the experiment show the composite confined concrete (CCC) had a higher bearing capacity and deformation ductility than the other groups of specimens. The initial prestress level increased from 0.3 to 0.4, the bearing capacity increased by 5.1%. As the distance between the centerlines of the steel hoop was reduced from 132 mm to 88 mm, the bearing capacity increased by 10.63%. The capacity of CCC is 1.61–1.78 times that of UC, 1.13–1.24 times that of SC, and 1.53–1.69 times that of PC. Based on the transverse reinforcement-confined concrete model of Mander, a composite confined concrete analysis model is proposed. Then the formula of bearing capacity of CCC column was established. The formula calculation results agree well with the experimental results. Compared with the SJ confined concrete, due to the presence of external PSH, the failure mode is changed, and the shear capacity of the composite confined concrete column is improved, thereby limiting the deformation of concrete and overcoming the tendency of diagonal cracks formation. This paper analyzes the shear failure mechanism of CCC based on the force balance model.