Structures are always exposed to the surrounding environment. The environmental variability (especially fluctuation in temperature) creates noticeable variations in structural modal properties. Two major mechanisms from temperature can cause uncertainties in natural frequency and mode shape measurements: i) the changes of material properties (elastic modulus) by temperature variation, and ii) the stress stiffening effects by temperature induced axial loading. Also, changes of boundary condition may cause variation in modal properties as well. In model updating, not considering these environmental effects may cause false identification on structural damage, thus compromises the accuracy of the updating results. This study presents a finite element model updating technique which can address the issue of varying environment including temperature variation and boundary condition changes. Temperature and boundary condition information is incorporated into the stiffness formulation of the finite element model. A numerical study on updating a bridge model subjected to damage and environmental changes is presented to demonstrate the effectiveness of the proposed method.
Changes in environmental conditions (such as temperature and humidity) and boundary conditions have been observed to have significant impact on structure's dynamic properties [1-6]. In general, environmental factors affect structures in a complicated manner such that it may result in support movement to strengthen or weaken the constraints . Such changes of boundary conditions also can lead to significant variation of structure’s modal properties. However, few studies have considered the existence of both temperature and boundary condition as the combined contributing factors in changing structure’s dynamic properties.
This paper proposes a numerical study to analyze structure’s dynamic properties under combined influence of temperature and boundary condition. A beam finite element model that can consider the changes in both temperature and boundary condition is established. Numerical study is conducted to reveal the relationship between the variation of the beam’s dynamic properties and the changes of its boundary condition as well as ambient temperature. The obtained conclusion will provide insights of the influence of these two factors on future dynamic based structural health monitoring studies.