Application of modal flexibility-based deflections for damage diagnosis of a steel frame structure

In this paper a modal flexibility-based approach for damage diagnosis is presented and discussed. Modal flexibility matrices of structural systems can be derived from vibration tests and changes in these matrices can be associated to structural damage. One of the main challenges is to apply modal flexibility-based methods on real-life civil structures, to detect damage on structures using ambient vibration data. A recent method has been formulated for damage detection, localization, and quantification of building structures; it is based on the modal flexibility-based deflections of such structures under uniform loads. The method was originally formulated for frame buildings that can be modeled as plane shear-type structures. The objective of the paper is to test this methodology on generic buildings that, in principle, cannot be easily modeled as plane shear-type structures. The method was applied to the ambient vibration data of a steel frame structure that has a monitoring system with acceleration sensors. Various damage configurations were induced to the structure by removing diagonal braces on the external surface of the frame. The results showed that the method is able to identify the stories and the directions of the frame that have been affected by the damage.