The effects of bond, shrinkage and creep on cracking resistance of steel and GFRP RC members

Abstract

The analytical and numerical models for combining the effects of bond, shrinkage, creep and ageing of concrete on the stress-strain state and cracking resistance of reinforced or prestressed concrete elements in a period prior to loading are proposed. A geometrical meaning of the coefficient of ageing is defined in terms of an average stress-strain approach. It is mathematically proven that this coefficient integrally establishes a continuous shape function of the actual concrete stress (or its increment) in a given period of time. This allows for substituting the rectangular stress diagram for the actual function of stress in time to attain the same areas of these diagrams and explicit predicting the stress-strain state in time by using algebraic equations for the inverse of Volterra integrals. The analytical formulae for predicting the cracking moment of the cross-section accounting for bond, shrinkage, creep and ageing of concrete are also proposed. It is demonstrated that the intense development of the partially recoverable instantaneous and creep strains play the main role. The proposed formulae are applicable to the assessment or retrofitting of the existing structures, where the full contact interaction techniques are inappropriate.