Finite element modal analysis and vibration-waveforms in health inspection of old bridges

• FE modal analysis based on vehicle waveforms is consistent with the field results.
• FE modal analysis of original maps can be used to investigate health of old bridges.
• Major physical damage on the bridge is mainly associated with the first mode.
• FE modal analysis based on vehicle waveforms can be used to guide bridge inspectors.
• Bridge's deterioration is associated with the traffic that excites the first mode.

The validity of using the finite element modal analysis in combination with the operational vibration-waveforms generated by vehicles to guide structural health monitoring observers in their inspection of old bridges is investigated in this work. A nondestructive vibration-based approach, operational response and waveform analysis (ORWA), is introduced and used in the process of validating the predictability of the finite element model. In ORWA, the frequency-domain response of a highway bridge is generated from the operating traffic load, and the structural response is visualized and used to develop a holistic view of the bridge's response to automobile loadings. By visualizing the response of the bridge, concrete cracking in the abutment and deck is correlated with certain types of structural motion and their corresponding frequencies. Significant excitation frequencies for this particular structure and loading are identified using a frequency-domain study of the vibration-waveforms generated by vehicle, and field results showed similarity with field impact tests conducted on the bridge. The finite element modal analysis of the original CAD drawings of the bridge in combination with the vibration-waveforms generated by vehicles spectrum has demonstrated realistic consistency with the findings of ORWA in showing the correlations between the physical damage areas on the bridge and the excited mode shapes of the operational loading that tend to cause these types of damage.