Coherent Lidars are able to finely measure the vibration velocity of remote targets. This allows Operative Modal Analysis (OMA) of potentially damaged buildings, for their diagnosis at a safe distance after a seismic event. As a next step from our previous work validating this method for modal frequency determination, we have assessed its capability to extract the full modal parameters of RC buildings, including mode shapes, using multiple ambient vibrations measurements by Lidar on the entire structure. We report on the development and field trial of a 3-path Lidar vibrometer for this purpose. After a description of the system, we show that application-related constraints are fulfilled: low velocity noise, real-time signal processing, compact and laser safety. Then, we present the results of a real-scale trial on 3 buildings in Grenoble, France. We discuss the reliability of this technique for remote structural diagnosis with a comparison of modal parameters, as measured by Lidar at 200m range and in situ velocimeters.

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Sponsor: Vulnérabilité des Ouvrages aux Risques VOR Program, Rhône-Alpes Council. Acknowledgment:This work was supported by the Rhône-Alpes Regional Council (Programme Vulnerabilité des Ouvrages aux Risques) and the Joseph Fourier Université (Grenoble 1).Using experimental data to reduce the single-building sigma of fragility curves: case study of the BRD Tower (Bucharest -Romania) ABSTRACT:The lack of knowledge concerning modelling existing buildings leads to significant variability in fragility curves for single or grouped existing buildings. This paper aims to investigate the uncertainties of fragility curves, with special consideration of the single-building sigma. Experimental data and simplified models are applied to the BRD tower in Bucharest (Romania), a RC building with permanent instrumentation. A 3-step methodology is applied, (1) adjustment of a linear MDOF model for experimental modal analysis using a Timoshenko beam model and based on Anderson s criteria, (2) computation of the structure s response to a large set of accelerograms simulated by SIMQKE software, considering twelve ground motion parameters as intensity measurements (IM), and (3) construction of the fragility curves by comparing numerical interstorey drift with the threshold criteria provided by the Hazus methodology for the slight damage state. By introducing experimental data into the model, uncertainty is reduced to 0.02 considering Sd(f 1 ) as seismic intensity IM and uncertainty related to the model is assessed at 0.03. These values must be compared with the total uncertainty value of around 0.7 provided by the Hazus methodology.