Thermal Environmental Effects on Modal Parameters and Health Monitoring of Bridge Structures

Often changes in the frequencies extracted from the vibration response are used for the detection of damage. However, these structural characteristics are also affected by the outside thermal envonment; this effect could be large enough to mask the changes caused by the damage. So it is important to understand and predict the effect of the environmental variations on these characteristics to separate them from those caused by the damage. In this paper, we examine the trends in the frequencies variations of a reinforced concrete box girder bridge structure subjected to a nine-year long record of measured temperature, radiation, and wind speed. It is observed that the major trends in the frequency variations are parallel to the major trends in thermal environment. The paper then presents and validates an identification approach to estimate the system frequencies directly from a few measured temperature values without a detailed finite element analysis.