Stiffness Characteristics of Composite Beams and Application in Damage Identification

Composite structures are used commonly in civil engineering; a typical example is a bridge deck consisting of concrete slabs and steel girder beams, in which shear connectors are used to connect the concrete slabs and steel beams to form a composite structure. The structural performance of a composite structure is well understood to depend not only on the properties of the primary components (slabs and steel beams) but also on the properties and condition of the shear connectors. Therefore, in a structural health monitoring and damage identification process, it is imperative to distinguish the damages in the primary components and in the shear connectors. However, in the existing literature concerning damage assessment of composite structures, there generally is a lack of differentiation between the damages in the two distinctive groups of constituent entities, and oftentimes the damages are treated simply in terms of the gross flexural stiffness with the use of an equivalent Euler–Bernoulli beam. This could result in a false identification of the actual severity of the damages, and even in misleading results. In this study, the basic mechanics governing the equivalent flexural rigidity and its distribution in a composite beam were investigated analytically, and the effects of the essential differences between the component beam damage and the shear connector damage on the distribution of the flexural rigidity were examined using numerical simulations. On this basis, the feasibility of differentiating the two types of damage from a damage identification process using vibration information, namely the natural frequencies and mode shapes, was demonstrated by means of a finite-element model updating procedure.