Nonlinear creep response of reinforced concrete beams

The nonlinear viscoelastic behavior of reinforced concrete beams under sustained loading is investigated in this paper.A theoretical model is developed, which is based on the viscoelastic modified principle of superposition, and accounts for cracking, nonlinear behavior in compression, shrinkage, aging, and the creep rupture phenomenon of concrete.A nonlinear form of the relaxation modulus is presented, which is introduced into the constitutive relations and the corresponding nonlinear rheological Maxwell model, to account for damage.The governing equations are solved through time-stepping numerical integration, which yields an exponential algorithm following the expansion of the relaxation modulus into a Dirichlet series.The determination of the section-equivalent rigidities and creep strains along the cracked and uncracked regions is achieved through an iterative procedure at each time step.The capabilities of the model are demonstrated through numerical examples and parametric studies including comparison with test results available in the literature.The results show that creep has various and different influences on the structural response, and in some cases it may lead to a reduction of the load-carrying capacity of the member by creep rupture-type of failures.