Experimental modal analysis of steel-concrete composite beams with partially damaged connection

One of the main difficulty connected to the use of dynamic methods for damage detection in structures lies on the small sensitivity of the dynamic parameters to damage. This is an intrinsic feature of structural diagnostics based on dynamic data and represents a source of important indeterminacy, such as the strong dependence of the results of damage detection techniques on the experimental errors and on the accuracy of the structural model that is cho-sen to interpret measurements. These facts are nowadays well known for simple structural systems, such as single beams or frames, but still are not completely clarified for more com-plicated structures. In this paper the results of an experimental investigation on the sensitivity of modal parameters of steel-concrete composite beams with partially damaged connection are presented and discussed. Dynamic tests were performed on two pairs of composite beams, whose connections have different linear densities, and four damage configurations for each beam were analyzed. Damage corresponds to a symmetric notch of increasing depth induced by saw-cutting one end connector of the composite beam. Natural frequencies and modal damping of the lower axial and flexural modes were assessed for the undamaged configura-tion and the four levels of damage. Flexural vibrating modes were assessed up to the fourth order mode