Modal damping as a damage detection parameter in reinforced concrete structures

Nowadays, damage detection by evaluation of changes in dynamic system characteristics (DSC's) such as eigenfrequencies, modal damping and mode shapes is a subject that has received considerable attention. While the relationship between eigenfrequencies, mode shapes and the crack damage in reinforced concrete (RC) structures has been already established, the case of damping has still to be well investigated. This paper deals with a finite element study of damping in reinforced concrete structures. A finite element model of a RC beam is achieved to understand the damping evolution due to a cracking process. A crack is simulated in the concrete matrix of the model perpendicularly to the reinforcement direction. The model is subjected to a uni-axial tensile loading and the stored strain energies during the simulated cracking process are numerically calculated. The damping of the RC beam is derived from the strain energy fractions. The evolution of the calculated damping is presented and commented in this paper.