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.The authors wish to acknowledge the grant SFRH/BSAB/114302/2016 provided by FCT
and the Australian Research Council grant DP150104107, as well as the support provided by
the UNSW for the research activities carried out under the status of Visiting Professorial
Fellow for the first author. The support of the FCT through the project PTDC/ECM EST/2635/2014 is also acknowledged
