Prediction of presence and severity of damages using experimental Mode Shape

Abstract

Global dynamic technique based on frequencies change is used to detect the damages/ cracks in structures. This technique is based on changes in natural frequencies. However, it is found that changes in frequencies are negligible even in major damage cases. Several researchers have used modes shape instead of frequencies to detect the damage/ crack in structure. It is true that mode shapes approach is better compared to frequencies based analysis for damage detection; however, it fetches excellent result, if real mode shape is used. Researchers are using theoretical/ numerical/ interpolated modes shape, which produce erroneous results. In this paper, a method is proposed to extract the real mode shape of structure experimentally using only one accelerometer and damage was detected successfully in the steel beam using this mode shape. An artificial damages were created in the steel beam in four stages and the mode shapes were determined after damage for each stage. The damage was also located and severity was predicted with the help of the extracted modes shape. It was found that location predicted by proposed method was almost correct. This technique is useful for sensitive structures.