Steel fibre-reinforced concrete: multi-scale characterisation towards numerical modelling

[摘要] ENGLISH ABSTRACT: In recent years, Steel Fibre-Reinforced Concrete (SFRC) applications have increased in quantity andvariety, due to its potential to partially or totally replace conventional reinforcement (rebar orwelded mesh). Methods for material characterisation, constitutive modelling and design musttherefore be improved in order to facilitate the demand for greater structural application of SFRC.A large database of experimental data and empirical models from the analysis of scaled or full-scaleshear-critical SFRC structural beams has accumulated. It is therefore concluded from a survey thatmaterial-level characterisation and constitutive modelling may be more beneficial in facilitating thedemand for greater structural application. Consequently, the primary mechanisms governing thefundamental behaviour of SFRC need to be characterised in order to produce a direct definition ofthe material's constitutive model.Far less work has been done on the direct shear response of fibre reinforced concretes. Even fewerinvestigations attempt to link the Micro-scale (i.e. the transverse pull-out of steel fibres) to theMeso-scale (i.e. at the scale of a single crack) for Mode II fracture. At the time of publication ofSoetens & Matthys (2012), only one other study, Lee & Foster (2006) was known that applies thismethod for investigating the Mode II fracture of SFRC.Analogous to existing numerical tools for reinforced concrete (RC) membrane elements, researchtowards a constitutive material model and numerical procedure for the analysis of SFRC membraneelements is considered to be essential. A direct and rational approach to model the generic materialresponse also has the potential to allow for tailoring and optimisation in material and structuraldesign.Three scales of observation or analysis are defined in this dissertation, namely the Micro-scale(single fibre level), Meso-scale (single crack level) and Macro-scale (structural level). Here attentionis given only to the Micro and Meso-scale.In order to contribute to multi-scale characterisation towards constitutive and numerical modelling,the outcomes of this dissertation in sequence are: Adapt a composite design procedure and developa SFRC; Classify the composite in terms of standard performance indicators and testing procedures;Design, fabricate and execute experimental tests to characterise the Mode I and Mode II fracture atthe Micro and Meso-scale of observation; Develop a material model and verify it numerically: Thisrequires the implementation of an analytical formulation of the material model into a numericalprocedure. The material model is calibrated with the experimental data and verified via a FiniteElement (FE) representation of the experimental Meso-scale test. Finally, an empirical model is alsodeveloped which reconciles the fibre component with the Mode II Meso-scale response.Two useful technologies are utilised to assist in material characterisation, Computed Tomography(CT-scan) and Digital Image Correlation (DIC). The CT-scanning facility provides valuable insight intothe fibre distribution and the ability to analyse and quantify the fibre orientation distribution is apowerful tool. The non-contact measurement method (Aramis DIC) proved invaluable in determiningthe specimen shear displacement and rotation.This dissertation provides insight into experimental design for the fundamental fracture modes ofSFRC. A contribution is made to the limited literature available on the link between the single fibretransverse pull-out response and the composite Mode II fracture behaviour. The numerical andempirical models developed simulate the composite response well, given their relative simplicity andlimited experimental data. The constitutive model and numerical procedure should aid in materialdesign and provide a foundation for defining material laws.

[发布机构] Stellenbosch University