Digitally fabricated weak interfaces to reduce minimum reinforcement in concrete structures

Abstract

Crack initiators in reinforced concrete structures can facilitate fulfilling the serviceability requirements. They can be used as a design parameter to diminish the minimum reinforcement for members subject to imposed deformation and exposed to the environment as they reduce the crack spacing and width when arranged close enough. While crack initiators in conventional concrete construction are cumbersome to provide (e.g., by construction joints or taperings), they are inherent to layered extrusion processes with digital fabrication technologies: the tensile strength is typically reduced locally in interfaces between layers. Rather than trying to avoid these weak interfaces, this paper discusses the potential of taking advantage of them to act as crack initiators reducing the minimum reinforcement content. A tension chord-based model is developed to (i) account for the local strength reduction and (ii) predict the effect of weak interfaces on the expected crack spacing and width. As a key finding, the model predicts a reduction of the required minimum reinforcement ratio proportional to the locally decreased concrete tensile strength for a specified maximum crack width requirement under imposed deformations. An experimental campaign on five layered and three reference tension ties confirmed the clearly positive impact of weak interfaces on crack spacings and widths.

Advances in Structural Applications of Digital Fabrication With Concrete

“…bond: Tensile tests on the postinstalled reinforcement shells showed no significant influence of the fabrication method [16], and the bond of conventional reinforcing bars between printed layers was higher than for conventional concrete [19]. The layering, typical for DFC processes, can have an effect on the cracking behaviour of concrete members that allows to reduce the reinforcement required for crack control [5].…”

“…Digital fabrication with concrete (DFC) has been proposed as one of the solutions to facilitate the fabrication of efficient concrete structures [3][4][5][6], as it allows (i) building complex shapes without high cost and (ii) tailoring the materials and their properties according to requirements. However, most digital technologies face difficulties penetrating the market due to the challenge of integrating reinforcement required to comply with existing building codes [7,8].…”