Effects of Changing Environmental Temperature on Finite Element Model Updating of the Dowling Hall Footbridge

This paper investigates the effects of changing environmental temperature on finite element (FE) model updating of the Dowling Hall Footbridge located at the Tufts University campus in Medford Massachusetts. The footbridge is equipped with a continuous monitoring system including eight accelerometers, ten thermocouples, a remotely-operable data acquisition system, and a communications system between the bridge and the laboratory. A set of data is recorded once an hour or when triggered by large vibrations. The monitoring system has been running continuously since January of 2010 and is still providing data. The modal parameters of the structure are extracted from the measured ambient vibration data using an automated data-driven stochastic subspace identification algorithm. The identified modal parameters are used to update the FE model of the footbridge. However, the identified natural frequencies show significant variability with changing environmental temperature. This variability propagates through the FE model updating process and therefore yields inaccurate updated FE model parameters. In this study, a polynomial model is estimated to represent the relation between measured temperatures and identified natural frequencies. Two sets of FE model updating with five substructures are performed based on 17 weeks of hourly identified modal parameters before and after removing the temperature effects. Variability in three out of five updating parameters is reduced when the effects of temperature were removed from the identified natural frequencies.