Assessment of Damage in Prismatic Beams Using Modal Parameters

Abstract

In this study, the modal parameters of un-cracked and cracked plain cement concrete prismatic beams have been studied. A crack in a beam element introduces considerable local flexibility, which has been expressed by local flexibility matrix, the dimension of which depends upon the numbers of degree of freedom considered. An approach based on linear fracture mechanics theory has been used to find flexibility matrix for the cracked element. The FEM program has been developed for eigen-value problems to determine the modal parameters of the cracked beams. Numerical studies are performed by considering simply supported beam with single and multiple cracks at different locations with different crack depths. The changes in displacement mode shapes are not localized in the region of damage and hence, they do not give indication of the location of damage very precisely. With curvature mode shape, the damage location can be attained in a very efficient manner. The absolute changes in the curvature mode shapes of the damaged and intact structure are localized in the region of damage and hence can be used to detect the damage in a structure. Curvature damage factors are also calculated with the help of curvature mode shapes for the number of modes considered to detect the damage in a structure.