Concrete creep and thermal stresses : new creep models and their effects on stress development

Sammanfattning: This thesis deals with the problem of creep in concrete and its influence on thermal stress development. New test frames were developed for creep of high performance concrete and for measurements of thermal stress development. Tests were performed on both normal strength and high performance concretes. Two new models for concrete creep are proposed. Firstly, a viscoelastic model, the triple power law, is supplemented with two additional functions for an improved modelling of the early age creep behaviour. Secondly, a new engineering creep model is proposed suited for design purposes. The basic feature of this model is based on the creep expressions in CEB/FIP Model Code 90. With both models good agreement were obtained with test results. The investigation on the influence of creep on thermal stress development showed that thermal stresses cannot be accurately evaluated without a correct consideration of the viscoelastic behaviour. Creep response during the three first days after load application seems to be the most important part of the creep spectra.