Tests on RC slabs reinforced with 500 MPa welded wire fabric

Abstract

Welded wire fabric, with a characteristic yield strength of 500 MPa, is commonly used by the Australian building industry in reinforced concrete slabs. Such steel has recently been classified in the steel reinforcement standard AS/NZS4671-2001 as Class L (low ductility). Reinforcement is classified as Class L if the minimum specified lower characteristic uniform elongation is at least 0.015 and the ratio of yield stress to ultimate tensile strength exceeds 1.03. A reinforced concrete flexural element reinforced with welded wire fabric invariably fails by fracture of the tensile reinforcement and the conventional understanding of ductile under-reinforced flexural failure is not valid. At the ultimate moment, fracture of the tensile steel may occur well before the concrete in the compression zone becomes overstressed, certainly well before the extreme compressive fibre strain reaches 0.003 (as specified in the Australian Standard for Concrete Structures, AS3600-2001). This can be readily shown using a simple cross-sectional analysis, assuming plane sections remain plane and enforcing the requirements of equilibrium and compatibility.It is important to verify the theoretical predictions with experimental results, as the catastrophic failure mode resulting from fracture of the tensile steel has direct consequences on ductility, warning of failure, moment redistribution in indeterminate structures and the validity of many of the routine approximations and simplifications made in the analysis and design of reinforced concrete structures. This paper presents experimental results of three simply supported and three continuous slabs, reinforced with Australian welded wire fabric, designed in accordance with AS3600.2 All slabs were observed to fail in a brittle and catastrophic manner, namely by fracture of the welded wire fabric, at the most heavily loaded section. The results have important implications for consulting structural engineers, code writers, and the builders, owners and users of concrete structures.