Time-Dependent Behavior of Concrete Beams

A nonlinear creep analysis for reinforced concrete beams is formulated by means of the ordinary flexure theory. The analysis is based on the assumptions that data from sustained load cylinder tests may be used to represent the stress-strain-time relation for the concrete and that this relation is unique, that is, independent of prior stress history. The stress-strain-time relation so obtained, and certain geometry conditions from the plane section hypothesis, are introduced into the beam equilibrium equations to give a set of simultaneous differential equations that govern the beam deformations. A numerical procedure for solving these equations is proposed and results are compared to measurements from laboratory tests. It is concluded that the theory is suitable for predicting creep deformations in beams under high sustained loads, but its application to the case of shrinkage in an unloaded beam or to the case of repeated loading is questionable. However, the proposed analysis may provide an important means for studying flexural strength characteristics of concrete beams under sustained loads.