Seismic damage diagnosis of a masonry building using short-term damping measurements Leonidas Alexandros S. Kouris a,b,c,n , Andrea Penna a,b , Guido Magenes a,b,c a University of Pavia, Department of Civil Engineering and Architecture, v. Ferrata 3, 27100 Pavia, Italy b European Centre for Training and Research in Earthquake Engineering, v. Ferrata 1, 27100 Pavia, Italy c Institute for Advanced Studies, IUSS Pavia, p.za della Vittoria 15, 27100 Pavia, Italy article info Article history: Received 23 April 2016 Received in revised form 11 January 2017 Accepted 1 February 2017 Handling editor: A.V. Metrikine Available online 12 February 2017 Keywords: Full scale shaking table test Unreinforced stone masonry building Random vibration tests Proportional damping Damage detection abstract It is of considerable importance to perform dynamic identification and detect damage in existing structures. This paper describes a new and practical method for damage diagnosis of masonry buildings requiring minimum computational effort. The method is based on the relative variation of modal damping and validated against experimental data from a full scale two storey shake table test. The experiment involves a building subjected to uniaxial vibrations of progressively increasing intensity at the facilities of EUCENTRE la- boratory (Pavia, Italy) up to a near collapse damage state. Five time-histories are applied scaling the Montenegro (1979) accelerogram. These strong motion tests are preceded by random vibration tests (RVT's) which are used to perform modal analysis. Two determi- nistic methods are applied: the single degree of freedom (SDOF) assumption together with the peak-picking method in the discrete frequency domain and the Eigen realisation algorithm with data correlations (ERA-DC) in the discrete time domain. Regarding the former procedure, some improvements are incorporated to locate rigorously the natural frequencies and estimate the modal damping. The progressive evolution of the modal damping is used as a key indicator to characterise damage on the building. Modal damping is connected to the structural mass and stiffness. A square integrated but only with two components expression for proportional (classical) damping is proposed to fit better with the experimental measurements of modal damping ratios. Using this Rayleigh order formulation the contribution of each of the damping components is evaluated. The stiffness component coefficient is proposed as an effective index to detect damage and quantify its intensity. & 2017 Elsevier Ltd. All rights reserved. 1. Overview of proposed methods to evaluate damage Damage detection and control of structures have been in the centre of vast and continuous research over at least the last four decades (to note only a few papers among others [1–53]). Usually most of the effort is spent to assess the deterioration of structural integrity due to environmental [4,23,30,54], seismic [48,53] or other sources (such as fatigue in mechanical equipment) using long term monitoring. In this sense, measurement periods may span over a year approximately. Two main trends have been followed to detect and localize damage (inverse engineering): (i) the direct method using the Contents lists available at ScienceDirect journal homepage: www.elsevier.com/locate/jsvi Journal of Sound and Vibration http://dx.doi.org/10.1016/j.jsv.2017.02.001 0022-460X/& 2017 Elsevier Ltd. All rights reserved. n Corresponding author at: University of Pavia, Department of Civil Engineering and Architecture, v. Ferrata 3, 27100 Pavia, Italy. E-mail address: leonidasalexandros.kouris@unipv.it (L.A.S. Kouris). Journal of Sound and Vibration 394 (2017) 366–391