Time-dependent analysis of reinforced and prestressed concrete plates using mixed finite elements

Abstract

Shrinkage and creep are concrete properties which induce delayed deformations, that are usually important in the design and construction of concrete structures. The complexity in the instantaneous analysis of plates justifies the usual approximations permformed in their analysis (such as, for example, the equivalent frame method, etc.). Certainly, this is also the case for time-dependent analysis of concrete plates (delayed effective modulus method and others being employed therein). This work presents a procedure for taking accurately into account the effects of shrinkage and creep in concrete polates. The methodology introduced these deformations as geometrical actions in a step by step procedure. Linear viscoelasticity is assumed for concrete because time-dependent analysis corresponds usually to structural service-abilirty conditions. Besides, concrete cracking can be taken into account, as well as the effects of active and passive reinforcement. The finite element method is applied for the analysis using the Reissner functional which is a very interesting alternative for plate analysis. Joining the procedure to introduce the delayed deformations and the method of analysis results in a very effiecient methodology for a time-dependent analysis of plates. Finally, two examples ilustrate the posibilities of the procedure.