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The influence of thermal effects on structural health monitoring of Attridge Drive overpass



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Structural Health Monitoring (SHM) comprises a wide range of techniques for the condition and damage assessment of an existing structure. Vibration-based damage detection (VBDD) techniques, a class of SHM methods, use changes in the dynamic properties (i.e., natural frequencies, mode shapes and damping characteristics) of structures to detect deterioration or damage. The application of VBDD methods to simple structures in a well-controlled laboratory environment has gained some successful results. However, the practical field application of VBDD still faces significant challenges since vibration measurement is subject to the influences of high levels of uncertainty in environmental, structural and loading conditions. In this thesis, the influence of temperature variations on the application of VBDD methods to an in-service complex structure was experimentally and numerically studied. The structure studied was the Attridge Drive overpass in Saskatoon, Saskatchewan. The main objective of this research was to assess the influence of temperature variation on the dynamic properties (natural frequencies and mode shapes) of the overpass, and on the ability of VBDD methods to detect and locate damage. Field dynamic measurements were made on the bridge on numerous occasions under a wide variety of ambient temperatures, using high sensitivity accelerometers and a temperature sensor. Dynamic excitation was provided solely by ambient traffic loading. Finite element models of the overpass were also created and manually calibrated to measured field data. The models were used to simulate the dynamic behaviour of the bridge at a variety of temperatures and under various states of small-scale damage. Numerical analysis was conducted to study the effect of ambient temperature on structure’s dynamic characteristics and to differentiate the patterns of mode shape changes caused by damage and ambient temperature. It was concluded that the change of ambient temperature mainly affects the elastic modulus of the construction materials and therefore stiffness of the entire bridge. As a result, the eigenfrequencies and mode shapes of the structure are influenced. The dynamic properties extracted from measured experiment data showed an approximately bilinear relationship between the three first natural frequencies and the ambient temperature. The natural frequencies for all three modes increased when the temperature fell. It was also found that, conceptually, it is possible to distinguish the patterns of mode shape changes caused by small-scale damage from those due to thermal effects, but only if a sufficient number of sensors are used to measure the mode shapes; in addition, those sensors must be located close to the damage location.



structural health monitoring



Master of Science (M.Sc.)


Civil and Geological Engineering


Civil and Geological Engineering


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