مقاله انگلیسی رایگان در مورد رفتار مکانیکی عناصر بتن مسلح متاثر از الیاف شیشه ای کوتاه و ویژگی‌ فضایی – الزویر 2022

Abstract

     Weft-knitted textiles made from high-strength fibrous materials offer great potential for use as a flexible stay-in-place formwork and reinforcement system since they allow creating complex geometries (i.e. doubly curved or folded) and introducing spatial features such as ribs within the fabric. However, the closed surface of the textile and its placement at the bottom edge of the concrete element present major challenges regarding bond, which may lead to premature failure due to delamination of the reinforcement initiated by a substantial opening of a governing crack. This study investigates the influence of short integral glass fibres and spatial bond ribs on the mechanical behaviour of weft-knitted textile reinforced concrete elements subjected to bending and their potential to increase the shear resistance. To this end, an experimental campaign consisting of 14 four-point-bending tests was conducted, where the specimens were examined regarding their load-deformation behaviour, crack kinematics and failure modes. The contribution of the short glass fibres to the load-bearing mechanism was estimated with Pfyl’s fibre engagement model, based on the material characterisation results from prism tests on fibre reinforced concrete members.

Introduction

     The urgent need for the construction industry to reduce its ecological footprint has led to numerous advances to decrease the volume of concrete consumption. Thereby, the use of conventional steel reinforcing bars presents an intrinsic limitation for lightweight concrete structures due to the minimum concrete cover needed to protect the reinforcement from corrosion (between 20 and 50 mm depending on the regional building codes and exposure). Textile reinforcement allows minimising the thickness of the concrete elements to a few millimetres when using non-corrosive materials such as aramid, carbon or glass fibres [1]. The mechanical behaviour of such fibres is usually linear elastic with high strength (3000–4000 MPa) at a moderate to high stiffness (glass fibre: ca. 70 GPa; carbon fibre: ca. 240 GPa). Textile reinforcement typically consists of rovings formed from multiple filaments, which exhibit lower strength and stiffness than the individual fibres due to several reasons: (i) the failure mode is brittle and does not allow for redistribution of stresses within the roving cross-section once the weakest fibre reaches its tensile strength [2], [3], [4]; (ii) commonly used fibres are sensitive to lateral loading and may be damaged due to deviations at the crack edges [5], [6]; (iii) the loads are transferred via inter-fibre friction within the rovings, which leads to an inhomogeneous stress distribution over the cross-section [7]; (iv) while the ribs in conventional deformed steel bars provide a proper force transfer between reinforcement and concrete [8], the bond of textile reinforcement mainly relies on adhesion and friction [9], [10], [11]. Coating or even fully impregnating the rovings (e.g. with epoxy resin) can attenuate these effects and may significantly improve the mechanical performance of the textile reinforcement [12], [13], [14].

Conclusions

     This study investigated the influence of short integral glass fibres and spatial features to improve the structural performance of concrete beams with weft-knitted textile reinforcement attached to the bottom edge of the specimens, especially regarding their shear strength and their resistance against delamination of the reinforcement. To this end, an experimental campaign consisting of 14 four-point-bending tests was carried out. The mechanical behaviour was examined regarding the load–deflection curves, the stress–strain relationship of the textile reinforcement and the crack kinematics based on the digital image correlation measurements, following the methodology presented in [20] to assess the response of the tension chord for concrete members subjected to bending./