Structural behaviour of post-installed reinforcement for 3D concrete printed shells – A case study on water tanks

Abstract

Incorporating sufficient reinforcement to ensure a ductile structural behaviour is a persisting challenge in digitally fabricated concrete structures. This paper investigates the structural performance of a reinforcement approach for 3D concrete printed elements, consisting of an unreinforced 3D printed concrete shell and a sprayed shell reinforced with a conventional reinforcing mesh for application in water tanks. Four reinforced concrete elements produced with this approach were tested in direct tension and compared to a reference test of a monolithic specimen to analyse the behaviour of circular water tanks under hoop stresses. Two eccentric reinforcement arrangements and two different printing patterns were investigated. Despite the testing setup not perfectly representing the actual behaviour of circular water tanks, in which shell deformations are kinematically restrained, the feasibility of the fabrication method could be examined. The results did not show significant differences in the behaviour of the different fabrication methods, with similar ductility as expected in a conventionally reinforced shell. The eccentric reinforcement caused the crack formation to originate on the surface close to the reinforcement, accompanied by out-of-plane deformations. The cracks on the far side of the reinforcement opened suddenly and reduced the out-of-plane deformations. The predictions with models neglecting the eccentricity of the reinforcement overestimated the crack opening. The best predictions were obtained from the tension chord model by only considering the concrete area defined by twice the mechanical cover of the reinforcement.