Comparison of Experimental and Operational Modal Analysis Results on Long-Term Monitoring of a Laboratory Truss Girder Subjected to Environmental Variability

Operational Modal Analysis (OMA) is a widely employed technique used whenever dynamic characteristics of large structures or buildings are investigated. The main benefit of this strategy is that it does not require any artificial excitation, since only the system’s outputs (acceleration, displacement) are necessary if the ambient excitation is enough. On the other hand, in literature it is often hypothesized that Experimental Modal Analysis (EMA) results are more reliable. Theoretically, dynamic characteristics such as natural frequencies, damping ratios and mode shapes processed through EMA and OMA techniques performed on the same structure should be coincident. In the present paper, a comparison between EMA and OMA tests on a laboratory truss girder subjected to environmental variability is presented. The structure’s dynamic and ambient conditions are constantly monitored in order to evaluate a long-term relationship between modal characteristics and environmental data. Due to extremely low ambient excitation, the structure is continuously forced every 30 min employing an electro-dynamic shaker with a random excitation. The forcing term, structure vibrations and environmental conditions are constantly measured with a data acquisition system including a load cell, 6 accelerometers and 4 thermocouples. The relationships between temperature and modal parameters estimated with both modal analysis techniques are compared in terms of data dispersion and linear correlation coefficient variation using data collected in long-term monitoring.