Damage Assessment of Reinforced Concrete Beams using Vibration Characteristics

Abstract

Civil Engineering structures comprise the bridges and buildings, and most of them are constructed using reinforced concrete. However, due to various factors like change in traffic density, environmental effects, and natural hazards, the structures are deteriorating before design life. Reinforced concrete bridges are more prone to these damages because they are constantly exposed to dynamic loads. Currently employed damage assessment techniques include biennial inspections which are also prone to lack of objectivity. The most popular damage assessment method, damage assessment using degradation in natural frequencies, has shown to be not much sensitive to damage and is reported to be influenced by environmental effects. Furthermore, the successful application of this method requires inverse engineering problem resolved which, again, has constraints due to the massive nature of the structures that doesn’t allow reproduce-ability at the laboratory scale. Recently, research has focused on investigating nonlinear behavior of concrete and incorporating in the health monitoring of civil infrastructure, while improving the SHM procedures in terms of inverse engineering problem and sensitivity. This research develops a plastic damage model and simulates the nonlinear behavior of concrete using finite element model of concrete. A comparison with the frequency degradation method, which does not show nonlinear bevhavior, is made in terms of sensitivity. The FE model of beam is simulated at different damage levels under various dynamic loads and various analysis have been performed which use linear and nonlinear approach. The comparison of Modal dynamic analysis and Implicit dynamic analysis shows that the implicit dynamic analysis is capable of reproducing the nonlinearities by showing the super harmonics and changes in modal frequencies for harmonic vibrations. Furthermore, the swept sine analysis shows the change variation in natural frequencies in damaged state with increase in amplitude.