Physical model for structural evaluation of R.C. beams in presence of corrosion

Corrosion of steel in concrete is a very common degradation phenomenon observed in reinforced concrete structures. It impairs the resisting section of the bars due to the change in the nature of material, the surrounding concrete around the steel bars because of the volume expansion effect of rust and finally modifies the bond between steel and concrete. Some experimental tests are present in literature in which the structural behavior of reinforced concrete beams in presence of corrosion of longitudinal bars and stirrups was analyzed: a progressive reduction of the load bearing capacity was demonstrated with an increase level of corrosion. Furthermore a not-obvious rupture mechanism was observed due to the effect of rust formation; in particular with the increase level of corrosion a change in the type of collapse was observed. In this paper a physical model based on the theory of plasticity is employed in order to explain the residual capacity of corroded beams. The model was developed for sound structures and is able to consider the interaction between shear and bending moment: this aspect is generally neglected following the codes prescriptions for structural evaluation but could become of importance when degradation takes place and determines changes in terms of mode failure. In this model the effect of corrosion is implemented in terms of section reduction and change of basic relationship of steel, degradation of concrete; a comparison with the reliable literature data is performed.