This paper investigates the nonlinear creep behaviour of concrete in compression and its relationship with cracking under uniaxial compression (cracks developing parallel to the loading direction). A physical model explaining the nature and the role of linear and nonlinear creep strains is presented, together with a failure criterion for concrete under sustained loads.
The model assumes that all nonlinear creep strains are due to concrete micro-cracking. The soundness of this assumption is checked against the experimental results obtained by the authors and by other researchers. The proposed model is shown to fit quite well the experimental results, for various load patterns and concrete ages.
The model also proves that the affinity hypothesis between linear and nonlinear creep strains (usually taken for granted in the design for stress levels below 70% of concrete strength in compression) is no longer valid when concrete fails under a sustained load, because of the unstable growth of cracking. Concrete response in these cases is analyzed in detail and a simplified but realistic approach for the evaluation of the failure envelope in compression is proposed.