A Modal-analysis-based NODIS Method for Beam-like Structure and its Performance under Changing Boundary Conditions

Abstract

Most widely studied Structural Health Monitoring (SHM) methods need baseline data from the undamaged state and a high number of sensors attached to the structure. In addition, environmental and operating conditions (EOC) can cause false alarms to the SHM system. Among all the EOCs, changing boundary conditions have a great influence on the signals. Thus, these methods are difficult to be applied in real structures for online monitoring. The aim of this study is to determine an efficient damage indicator based on the vibration information of the structure and evaluate the influence of boundary conditions on this method. Based on the structural mode shapes, the NOde DISplacement (NODIS) method which inspects the nodes or stationary points in the displacement mode shape is proposed in this paper. The advantages of this method are: (1) baseline-free, in terms of the comparison with a reference signal is not needed, (2) only a relatively small number of sensors are required. However, the performance of NODIS method under changing boundary conditions needs to be studied intensively. In the present paper, an experiment is conducted on a cantilever beam to investigate the influence of the boundary condition on NODIS method. A Transfer-Function-based Damage Index (TFDI) and wavelet analysis are adopted to investigate the characteristics of the influence