Estimation of modal masses for an in-service structure by transformation in the state space

This paper focuses on estimating the modal parameters of in-service infrastructures, applied to the pedestrian footbridge of the Science Museum of the city of Valladolid (Spain). The work consists not only on determining natural frequencies and damping factors associated to each of the estimated modes, as many commercial software provide from acceleration measurements through OMA (Operational Modal Analysis) and/or EMA (Experimental modal Analysis), but also to calculate the generalized masses corresponding to each of the estimated modes of the structure. For this purpose, firstly a dynamic representation of the system is obtained in the state space by SSI technique (Stochastic Subspace Identification) and secondly, by the appropriate transformation matrix, it leads to the representation that identifies the physical parameters of the system (matrices of mass, damping and stiffness), which allows to obtain modal masses and/or normalized mode shapes with respect to the mass matrix, which is the main contribution of the practical methodology presented in this paper. (C) 2016 CIMNE (Universitat Politecnica de Catalunya). Published by Elsevier Espana, S.L.U. This is an open access article under the CC BY-NC-ND license