Assessing the performance of subspace-based modal identification procedures for systems subjected to structural damage and Coulomb-friction non-linearities

Abstract

In this paper, the robustness of subspace-based identification methods for modal analysis is assessed for damaging systems including local Coulomb-friction mechanisms (or equivalently elasto-plasticity). The underlying objective is to capture damage-induced modal feature changes of structures, mainly frequency drop-off and damping increase, knowing that the presence of components with participating friction forces also affects modal signature. The performance of several modal detection procedures is assessed using the data acquired during the JVP (french for ‘Jonction Voile-Plancher’) test campaign during which a reinforced-concrete specimen, anchored to a shaking table by the means of swivels, is submitted to several kind of ground motion inputs of varied level. A comparison between Input/Output versus Output-Only identification is made using both seismic and broad-band random inputs and the potentialities of the modal selection procedures are highlighted for different cases where the two kind of non-linearities (damage occurrence and friction at swivels) are activated in different proportions. Regarding the presence of friction forces when conducting modal analysis, experimental results are backed up by a numerical study that enables a theoretical quantification of the apparent frequency and damping ratio values that should be expected after modal analysis for varied input-to-nonlinear forces ratios.