Smeared-bar model for viscoelastic analysis of uncracked reinforced concrete structures

This paper presents a technique for computing the time-dependent behavior of reinforced and prestressed concrete as a composite material. This technique, when implemented in a finite-element model and assuming that the concrete and steel reinforcement act as a composite material, is computationally advantageous compared with explicitly modeling the concrete and steel materials separately. The method is developed assuming linear viscoelasticity and uncracked sections. The approach starts by first approximating the creep compliance functions for the viscoelastic concrete as a Kelvin chain model. This approximation allows the viscoelastic behavior to be framed as a rate-type creep law, which converts the analysis to an equivalent elastic problem, simplifying the computations. This approach, originally developed for plain concrete, is extended in this paper to account for the effects of linear elastic reinforcement. Several implementation examples are provided documenting the viability of the method for problems of uniaxial, multiaxial, and bending behaviors. For the presented cases, the composite method is shown to provide similar results compared with models containing explicitly modeled reinforcement. The paper concludes with a discussion regarding how to extend the methodology to the general case with linear viscoelastic reinforcement and matrix materials.