Investigation into vibration-based structural damage identification and amplitude-dependent damping ratio of reinforced concrete bridge deck slab under different loading states

Vibration-based structural health monitoring (SHM) is based on the fact that changes in the dynamic characteristics of a structure are associated with structural damages. Deterioration in reinforced concrete (RC) bridge deck slabs is often observed during their service life due to fatigue and rebar corrosion leading to internal deterioration and damage, such as horizontal cracks. Since the internal deterioration and damage of RC slabs are often difficult to detect by visual inspection, a study was carried out to investigate such damages through vibration-based SHM. This study investigated experimentally the effect of horizontal crack and damage at different loading states, from 0 kN to load after failure, on the modal properties of RC slabs. Eigensystem realization algorithm and continuous wavelet transform approaches were adopted to identify the modal properties. Finite element model was developed to compare the experimental modal properties to the numerical ones. Changes in the natural frequency, modal damping ratio and coordinate modal assurance criteria were found to be correlated with damage. The correlation between damping ratio and damage was improved by considering the amplitude dependence of damping ratio. Investigation of amplitude-dependent damping behavior of RC slabs indicated variation in the slope of correlations between the amplitude and damping ratios with the vibration mode and structure condition in different loading states.