Ambient environmental effects on experimental modal analysis

Experimental modal analysis is an effective, nondestructive method to extract several important physical characteristics of a structural system, such as the mode shapes (deflected form), the natural frequencies of the modes that are excited, and an approximation for the component stiffness. Through past experiences, the authors have identified that the ambient environmental factors, such as temperature and humidity, have an effect on obtained natural frequencies. This finding of the authors agrees with findings published elsewhere. In order to further investigate the issue and quantitatively determine the effect of these factors on modal behavior, this study applies experimental modal analysis on a model timbrel vault. The model dome is constructed at the Peter Kiewit Institute-Structures Laboratory at the University of Nebraska, and stored outside where it is subject to fluctuations in ambient environmental conditions. Experimental modal analysis is performed over a four-month period on the model, and the ambient temperature and relative humidity are recorded. A database is created that includes temperature, relative humidity, measured mode shapes, and natural frequencies. The effects of temperature and humidity on the mode shapes are considered individually and collectively, and correction factors are presented.