Vibrations of steel–concrete composite beams with partially degraded connection and applications to damage detection

Vibrational methods are frequently used as diagnostic tools to detect damage in structures. One of the main difficulties connected with the use of such methods lies in the small sensitivity of the dynamic parameters to damage. This is an intrinsic feature of structural diagnostics based on dynamic data. It represents a source of important indeterminacy, such as the strong dependence of the results of identification on the experimental errors and on the accuracy of the structural model that is chosen to interpret measurements. Application of dynamic techniques to the case of steel–concrete composite beams, in addition, makes the problem more complicated, owing to the uncertainty about the mechanical behaviour of the connection and damage modelling. Previous research on vibrational methods for damage detection in composite beams was concerned with the identification of severe levels of damage. In this paper we present an Euler–Bernoulli model of composite beam which accurately describes the dynamic response measured on composite beams with either severe or intermediate levels of damage. A diagnostic technique based on frequency measurements is then applied to the suggested model and it gives positive results. A Timoshenko model of composite beam is also derived and used for diagnostic purposes.