Abstract
This paper is the first in a series of papers that present a new prediction model for creep and shrinkage of concrete, called for brevity the BP−KX model. This model represents an update and improvement of the BP model published in this journal in 1978–79. The improvement is possible because further experimental data became available in the literature and at the same time knowledge of physical concepts and mechanisms has improved. This first paper presents a prediction model for the mean (overall) shrinkage strain in cross-sections of long members, which takes into account the influence of environmental humidity, the effective thickness of the member, the effect of cross-section shape, the effect of age at the start of drying, and the effect of temperature. The proposed basic form of the shrinkage formulae is fustified by nonlinear diffusion theory for the movement of moisture through concrete. Extensive comparisons with important test data from the literature, altogether 23 data sets, reveal that the predictions are better than with the previous models. Statistics of prediction are also given. The main error of prediction arises from the estimation of the shrinkage parameters from concrete strength and composition. If limited short-time shrinkage data are available, the predictions can be greatly improved.
Resume
Ce rapport est le premier d’une série présentant un nouveau modèle de prédiction du fluage et du retrait du béton dénommé, pour abréger, modèle BKP. Ce modèle représente une mise à jour et une amélioration du modèle BP décrit dans ce journal en 1978/79. Des données expérimentales ultérieures disponibles dans la littérature, en même temps qu’une meilleure connaissance des concepts et mécanismes physiques, ont permis ce progrès. Ce premier rapport présente un modèle de prédiction pour une contrainte de retrait moyenne dans les sections transversales de longs éléments, qui prend en compte l’influence de l’humidité ambiante, l’épaisseur effective de l’élément, l’influence de la forme de la section, de l’âge au début du séchage et de la température. On justifie l’expression de base des formules de retrait par la théorie de la diffusion non linéaire pour la circulation de l’humidité dans le béton. De vastes comparaisons avec d’importantes données d’essai prises dans la littérature-en tout 23 séries d’essai-ont montré que les prédictions étaient meilleures qu’avec les modèles précédents. On donne aussi des statistiques de prédiction. L’erreur de prédiction principale provient de l’évaluation des paramètres de retrait à partir de la composition et de la résistance du béton. Si l’on dispose de données de retrait limité, les prédictions peuvent être considérablement améliorées.
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Bažant, Z.P., Kim, JK. & Panula, L. Improved prediction model for time-dependent deformations of concrete: Part 1-Shrinkage. Materials and Structures 24, 327–345 (1991). https://doi.org/10.1007/BF02472066
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DOI: https://doi.org/10.1007/BF02472066