Analitical approach for serviceability time-dependent analysis of reinforced concrete cross-sections. Proposal of a new factor for delayed deflection calculation

Abstract

This paper presents an approximate way for the time-dependent analysis of a reinforced concrete cross-section with reinforcement in both sides, in serviceability conditions (under permanent loads and after cracking), considering shurnkahe and creep in the compressed region. Being an analytical approach involved, some attention is paid to justify its fundamental assumptions. Finally, as a consequence, for practical calculations a formula, with several optional shapes, is proposed for the factor that permits to obtain delayed deflections from instantaneous ones. It could be an alternative to the current one existing at the Spanish reinforced concrete code (EH-88) and at its new version proposal (EH-91). The formula has the important quality of making explicit the incidence of both shrinkage and creep, properties having variations from one case to another; by other hand, in spite of having a similar formulation, it offers normally rather different numerical results.