A damage identification procedure for steel truss

This paper addresses the problem of identifying structural damage affecting one element of a steel truss. The purpose is to detect damages in relation to their magnitude, location and extension. A planar model of a damaged steel truss is used to illustrate the procedure. The direct problem is addressed by FEM, proposing the local stiffness of a damaged truss element. A modal identification is first implemented to obtain dynamic characteristics: natural frequencies, damping ratios and mode shapes. Damage is described as a reduction of the truss cross section, and defined in terms of its magnitude, extent and position. Moreover, a damaged element stiffness matrix has been derived and implemented within of a classical FEM procedure to obtain a numerical model used to generate a pseudo-experimental dynamic structural response under environmental noise. Then, Stochastic Subspace Identification (SSI), is carried out to extract and identify the main modal parameters related to both damage and undamaged truss system. A damage index is defined to evaluate the effectiveness of the proposed procedure.