Observed Variations of Mode Frequencies of a Prestressed Concrete Bridge with Temperature

Modal frequencies derived from experimental motion measurements have been shown to be useful measures for indicating the presence of perturbations in structures. The sensitivities of modal frequencies to different types of structural change can be quantified through the use of finite element models, and the comparison of experimental modal frequencies with FEM models is now an accepted practice for the initial analysis of experimental motion data. However, most structures are directly exposed to the environment and are thus subjected to variations in temperature, humidity, insolation as well as other influences which may mimick actual structural change. The extent literature appears to indicate that the sensitivities of the mode frequencies to temperature are of the same order as those predicted to occur for small but significant structural modifications. In view of this observation, there is a great need for further data which can be used to develop statistically reliable temperature corrections and to establish long-term repeatability of the corrections. To this end, this paper presents preliminary correlations of the modal frequencies with seasonal temperature variations during a seven month period of observation of a large-span pre-stressed segmental concrete bridge, during a time when outside air temperatures ranged from —15 (C) to 33 (C), which may be useful for this purpose.