Fibres as shear reinforcement in RC beams: an overview on assessment of material properties and design approaches

Abstract

It is recognized that understanding at a material level is needed in the development of rational, physical-mechanical, models for predicting the behaviour of fibre reinforced concrete at service and strength limit conditions. To this end, understanding the post-cracking mechanisms of the fibres, and their symbiotic relationship with the cementitious matrix that surrounds them, is required for the development of realistic modelling approaches that accurately represent empirical observations. Several experimental test setups and inverse analysis procedures have been proposed to derive the fundamental stress-crack width (–w) law, but a consensus still does not exists on the best strategy for its determination. In structures governed by shear, fibre reinforcement increases the stiffness and shear stress transfer across a crack, but a methodology to capture the contribution of fibres in this regards is challenging. To overcome this, a clear strategy is needed in deriving relationships that simulate fibre reinforcement mechanisms in the mobilized fracture modes and, also, develop design approaches capable of capturing the relevant contributions of the fibres. This study firstly reviews current inverse analysis models used to describe the tensile (Model I fracture) relationship for FRC and, secondly, discusses a newly proposed model, referred to as the integrated shear model (ISM). The ISM is developed from mesoscale observations from gamma- and X-ray imaging on FRC elements under Modes I and II fracture conditions. The resulting model is compared to test data reported in the literature and a good correlation is observed.