Multistage damage detection of a transmission tower: Numerical investigation and experimental validation

When vibration-based damage detection methods are applied to a large transmission tower for damage detection of loosened bolts, a number of obstacles exhibit. The global stiffness matrix, modal parameters, and global dynamic responses are not sensitive to local damage (loosened bolts) of a large transmission tower. The one-stage damage detection is inaccurate and sometimes impossible due to too many unknown damage parameters and seriously ill-conditioned inversed problem for a large transmission tower. Therefore, a new multistage damage detection method incorporating with a multiscale finite element (FE) model and a multitype sensor placement is proposed in this paper for the damage detection of loosened bolts of a large transmission tower. The methodology of multistage damage detection of the transmission tower with loosened bolts is first introduced. The numerical study with the multiscale FE model and the multitype sensor placement is then conducted to demonstrate the feasibility and accuracy of the multistage detection method using a large transmission tower testbed. The experimental validation is finally performed on the testbed to ascertain the effects of uncertainties involved in the numerical study on damage detection results. Both the numerical and experimental studies manifest that the proposed multistage detection method can effectively identify the loosened bolts in a joint of the transmission tower.