Michele Dilena

A Damage Analysis of Steel-Concrete Composite Beams Via Dynamic Methods: Part II. Analytical Models and Damage Detection

This paper is the second part of an experimental-analytical investigation on the dynamic behavior of damaged steel-concrete composite beams. In the first part of the research, we presented and discussed the experimental results of a comprehensive series of dynamic tests performed on composite beams with damage in the connection. Experimental observations suggested the formulation of a composite beam analytical model, where the strain energy density of the connection also includes an energy term associated to the occurrence of relative transversal displacements between the reinforced concrete slab and the steel beam. A comparison with experimental results shows that the model enhances accuracy in describing the undamaged state of composite beams and that it is also appropriate to accurately predict the dynamic behavior under damaged conditions. A damage detection technique based on the measurement of variation in the first flexural frequencies was then applied to the suggested model and gave positive results.

Experimental Modal Analysis of Steel Concrete Composite Beams with Partially Damaged Connection

One of the main difficulties connected with the use of dynamic methods for damage detection in structures lies in 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 chosen 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 complicated structures. In this paper we present and discuss the results of an experimental investigation on the sensitivity of modal parameters of steel-concrete composite beams with partially damaged connection. Dynamic tests were performed on two pairs of composite beams, whose connecdons have different linear densities, and four damage configurations for each beam were analyzed. Damage corresponds to a symmnetric 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 configuration and the four levels of damage. Flexural vibrating modes were assessed up to the fourth-order mode.

Damage Identification in Beams from Changes in Nodes of Mode Shapes

It is known that the effect of a single crack in an axially vibrating rod causes the nodes of the mode shapes to move toward the crack. In this paper an investigation of the analogous problem for a beam in bending vibration is presented. The monotonicity property linking changes in node position and crack location does not hold in the bending case. The analysis of the direct problem, however, shows that the direction by which nodal points move may be useful for predicting damage location. Analytical results agree well with experimental tests performed on cracked steel beams.