Damage assessment in reinforced concrete using spectral and temporal nonlinear vibration techniques

Both linear and nonlinear (amplitude-dependent) acoustical experiments are performed on a reinforced concrete (RC) beam in which damage is gradually induced by means of static loading tests. At different levels of damage, a complete experimental modal analysis (EMA) is carried out, assuming the structure to behave linearly. The analysis in terms of modal curvatures indicates a gradual reduction of the bending stiffness along the beam. Strong amplitude dependence of the linear dynamic behavior is observed as damage increases. After each loading step, measurement of resonant frequencies and damping ratios as function of vibration amplitude are performed, both using a frequency domain technique and a time domain technique. The nonlinearity is quantified as function of the damage. We compare the results of the linear and nonlinear techniques, and value them against visual damage and local bending stiffness. (C) 2000 Elsevier Science Ltd. All rights reserved.