ALKALI AGGREGATE REACTION IN NUCLEAR CONCRETE STRUCTURES: PART 4: MODELLING AND ANALYSIS

摘要

A two-dimensional nonlinear finite element analysis program, VecTor2, was adapted to the analysis of the effects of alkali silica reaction (ASR) (a type of alkali aggregate reaction (AAR)) in concrete structures. The theoretical bases for VecTor2 are the Modified Compression Field Theory (Vecchio and Collins, 1986) and the Disturbed Stress Field Model (Vecchio, 2000) - conceptual models for reinforced concrete based on a smeared rotating-crack macro-modelling approach. This paper focuses on the implementation of ASR constitutive models within the architecture of VecTor2, and on the modelling aspects of ASR-affected elements. The ASR expansion is treated as non-recoverable offset strains using a computational procedure previously developed for elastic and plastic offset strains (Vecchio, 1992). Two distinct mechanisms have to be taken into account to fully consider the effects of ASR: material expansion and changes in mechanical properties. The ASR-induced expansion may be evaluated, by various alternative models, as: (a) a uniform expansion, equally distributed in all directions; (b) an expansion limited by confinement, independently evaluated in each direction, (c) a volumetric expansion, redistributed in each direction or (d) as a consequence of the gel pressure. The changes in mechanical properties may be calculated as a function of the current free expansion, as recommended by ISE (1992). The Canadian Nuclear Safety Commission (CNSC) initiated and funded a comprehensive study currently under way at the University of Toronto. The scope and activities to be performed are described in detail by Orbovic et al. (2015). The outcome of this study is anticipated to reveal the implication of concrete deterioration due to ASR on structural integrity and includes material (Gautam et al., 2015) and structural testing (Habibi et al., 2015), and modelling. Validation studies were performed at both material and structural levels, by modelling ASR-affected specimens reported in the literature. The analytically determined responses currently show reasonable agreement with the experimental results. Accuracy is expected to increase when improved constitutive models are drawn from the material-level investigation (Gautam et al., 2015) and structural testing program (Habibi et al., 2015), concurrent parts of this study.