Structural damage in reinforced concrete beams leads to stiffness degradation, which alters the dynamic characteristics of the structure. Early identification of such damage is essential for ensuring structural safety and serviceability. This paper presents a numerical investigation of modal-based damage identification in reinforced concrete beams using vibration characteristics obtained from finite element analysis. A simply supported reinforced concrete beam is modelled using the finite element method, and damage is simulated by introducing localized stiffness reduction in a selected beam element.
Modal analysis is performed for healthy and damaged beam configurations to extract natural frequencies and mode shapes. Damage identification is carried out using three vibration-based indicators: natural frequency variation for damage detection, mode shape curvature for damage localisation, and modal strain energy for damage severity assessment. Multiple damage scenarios corresponding to 10%, 20%, and 40% stiffness reduction are considered to evaluate the sensitivity of the adopted methods.
The numerical results indicate a consistent reduction in natural frequencies with increasing damage severity, confirming their effectiveness in detecting the presence of damage. However, frequency-based indicators alone are insufficient for precise damage localisation. The mode shape curvature method successfully identifies the location of damage along the beam length for all damage cases, while the modal strain energy method provides a reliable quantitative measure of damage severity. A comparative assessment demonstrates that the combined application of mode shape curvature and modal strain energy methods offers a robust and comprehensive framework for vibration-based damage identification in reinforced concrete beams.
Keywords: Structural health monitoring; Reinforced concrete beam; Modal analysis; Damage identification; Mode shape curvature; Modal strain energy; Finite element method