Stiffness characteristics of composite beams and application in damage identification

Composite structures are commonly used in civil engineering; a typical example is a bridge deck consisting of concrete slabs and steel girder beams, where 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. In the existing literature conceming damage assessment of composite structures, however, there is generally a lack of differentiation between the damages in the two distinctive groups of constituent entities, and oftentimes the damages are simply treated 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 misleading results. In this study, the basic mechanics goveming the equivalent flexural rigidity and its distribution in a composite beam are investigated analytically, and the essential differences between the component beam damage and the shear connector damage on the distribution of the flexural rigidity is examined by 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, is demonstrated by means of a finite element model updating procedure.