Thin-walled concrete beams with stay-in-place flexible formworks and integrated textile shear reinforcement

Abstract

Thin-walled textile-reinforced concrete beams have recently emerged as a promising approach for material-efficient design. However, the increased complexity of the formwork is a major challenge in implementing such elements for broader use in the construction industry. This study presents a novel type of stay-in-place flexible formworks with integrated textile reinforcement. The use of weft-knitted textiles allows the integration of continuous high-strength rovings as shear reinforcement and the introduction of spatial features within the fabric to guide bending-active rods to shape the complex cross-section geometry. The manufacturing procedure and the structural performance were investigated in an experimental campaign consisting of four concrete beams with I-profile cross sections tested in three-point bending, where aramid rovings were used for the shear and conventional deformed steel bars for the flexural reinforcement. The transverse reinforcement ratio proved to be essential in increasing the shear strength. Thereby, the use of digital image correlation measurements of the surface deformations allowed the direct assessment of the strains and, thus, the mechanical activation of the textile reinforcement. The full tensile capacity of all the aramid rovings crossing the governing crack could not be exploited due to the brittle material behavior, resulting in a progressive failure once the first roving reached its tensile strength. Compatibility-based stress fields were used to predict the load-deformation and failure behavior of the tested beams, which resulted in an excellent agreement of the ultimate loads and failure modes obtained from the model with the observations and results from the experiments.