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In vibration-based condition assessment exercises, it is necessary to discriminate the variation of structural properties due to environmental changes from those caused by structural damage. Some efforts have been made to correlate the structural vibration characteristics and the air temperature or temperatures at the structural surface. As the temperature of an entire structure is generally non-uniformly distributed, using the air temperature or surface temperatures alone may not sufficiently capture the relation between the structural responses and temperatures. The present paper aims to investigate the variation of the structural vibration characteristics versus the non-uniform temperature field of the structure. Thermodynamic models are employed to estimate the temperature at different components of the structure at different time.As the material mechanical properties are temperature dependent, the structure can be regarded as a composite structure consisting of elements with different Young's moduli.Consequently the natural frequencies of the structure can be calculated with the finite

Monitoring deformation of super-tall structures under different environmental conditions is an important and challenging issue in assessing the safety and serviceability of structures. This paper presents a new method for calculating structural deformation using real-time strain data, which can be easily measured at different sections. Assuming the structural deformation is of bending beam type, the deformation of the structure is associated with longitudinal strain. Virtual work theory is then used to calculate the horizontal displacement and tilt angle of the building on the basis of the strain data at different heights of the structure. The proposed method is applied to the 600 m tall Canton Tower (previously known as Guangzhou New TV Tower), on which a long-term structural health monitoring system including over 400 vibrating strain gauges has been installed at different heights. The displacements and tilts of the structure top under normal and typhoon conditions are calculated using real-time monitoring strain data. The calculated deformations show good agreement with the measurements by using global positioning system (GPS) and inclinometers. The temperatureinduced maximum daily movement is similar to the value of typhoon-induced motion. Moreover, the displacement mode of the super-tall structure is also calculated and shows the bending type. Error analysis demonstrates that the calculated displacements have higher accuracy than the GPS-measured counterparts, and that the calculated tilts have similar accuracy as those measured by an inclinometer.

Abstract:The substructuring technology possesses much merit when it is utilized in model updating or damage identification of large-scale structures. However, the conventional substructuring technologies require the complete eigensolutions of all substructures available to obtain the eigensolutions of the global structure, even if only a few eigensolutions of the global structure are needed. This paper proposes a modal truncation approximation in substructuring method, in which only the lowest eigensolutions of the substructures need to be calculated. Consequently, the computation efficiency is improved. The discarded higher eigensolutions are compensated by the residual flexibility. The division of substructures and the selection of master modes in each substructure are also studied. The proposed substructuring method is illustrated by a frame structure and a practical bridge. The two case studies verify that the proposed method can improve the original substructuring method significantly.

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