Model updating based structural damage detection of transmission tower: experimental verification by a scaled-model

Transmission towers play a significant role in the distribution of electrical power. With the recent collapse of transmission tower at Sichuan, China on December 14, 2011, Structural Health Monitoring (SHM) of transmission towers becomes a hot research topic. According to the literature, it is impractical and impossible to develop a "general" method that can detect all kinds of damages for all types of structures. A practical method should take the characteristics of the type of structures and the kind of damages into consideration. For transmission towers, the buckling of secondary members (braces) due to strong wind during typhoon is not uncommon. The vibration of the tower caused by external excitations due to wind and workers during maintenance contains information about the structures stiffness and mass distribution. Therefore, it is possible to detect damages on the tower based on the measured vibration responses of the structure. This paper reports a feasibility study on the use of vibration data of transmission towers in the detection of damaged braces by following a model-based approach. A three-dimension finite element model (FEM) program was developed in MATLAB® for the computer modelling of the target transmission tower in this paper. A newly developed substructure-based structural model-updating scheme is employed to identify the stiffness distributions of the target transmission tower under the undamaged and damaged conditions based on the corresponding sets of measured modal parameters. By comparing the identified stiffness distribution, the damage locations and the corresponding extents can then be estimated. The contributions of this paper are not only on the development of the substructure-based model updating scheme but also on the verification of the proposed methodology through measured data from a scaled transmission tower model under laboratory conditions.