Abstract
We analyse the effect of temperature and wind velocity on the natural frequencies and modal damping ratios of the Faculty of Engineering Tower at the Università Politecnica delle Marche, a 10-story reinforced concrete frame building, permanently monitored with low-noise accelerometers. The data recorded over the first 5 months of monitoring demonstrate that temperature variations and wind intensity have a clear effect on the first three natural frequencies and the corresponding damping ratios. Temperature is positively correlated to the first and second frequencies, corresponding to shear displacement modes and negatively correlated to the third frequency, corresponding to a torsional mode. All frequencies are positively correlated to wind velocity and changes in damping ratios are inversely correlated to any change in frequency. A mechanical explanation of these phenomena is offered, based on a critical review of literature case studies. These results suggest that using changes in modal parameters for damage detection always requires accurate knowledge of the correlation between modal parameters and environmental quantities (temperature, humidity, and wind velocity), an information which is only available through long-term continuous monitoring of the structural response.
Highlights
Vibration-based Structural Health Monitoring (SHM) refers to a family of methods pretending to gain information on the damage state of a structure through measurement and analysis of its vibration response
While it is generally true that a structural damage produces changes in the dynamic response, it is not true that any change in the dynamic response is the result of a damage: notably, environmental conditions may produce variations of modal parameters in the same order of those induced by damage and often much bigger
We discussed the effect of temperature variations and wind intensity on the fundamental frequencies and modal damping ratios of the Universita Politecnica delle Marche (UnivPM) Faculty of Engineering Tower, a 10-story r.c. framed building, permanently monitored with low-noise accelerometers
Summary
Vibration-based Structural Health Monitoring (SHM) refers to a family of methods pretending to gain information on the damage state of a structure through measurement and analysis of its vibration response. Vibration-based structural damage detection of civil structures dates back to the early 1980s, as documented by extensive technical literature reviews [2,3,4] These early studies include development of methods for optimal sensor placement, selection of the most sensitive parameters to damage, and the definition of techniques to separate changes in the dynamic properties caused by damage from those due to environmental and operational conditions [3]. To this purpose, a permanent monitoring system, based on traditional wired low-noise accelerometers, has been installed to record the dynamic properties of the Tower and their changes with respect to the wind intensity and temperature variations. The monitoring system is described and the results of measurements are presented and discussed, adopting a multiple data regression to interpret effects of ambient parameters variations on modal properties
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