Monitoring historical masonry structures with operational modal analysis: Two case studies

Abstract

Two monuments in Portugal are being monitoring by the University of Minho: the Clock Tower of Mogadouro and the Church of Jerónimos Monastery, in Lisbon. Vibration sensors and temperature and relative air humidity sensors are installed in the two monuments. Operational modal analysis is being used to estimate the modal parameters, followed by statistical analysis to evaluate the environmental effects on the dynamic response. The aim is to explore damage assessment in masonry structures at an early stage by vibration signatures as a part of a heath monitoring process to preserve the historical constructions. The paper presents all the preceding dynamic analysis steps before the monitoring task, which includes the installation of the monitoring system, the system identification and subsequent FE model updating analysis, the automatic modal identification and the investigation of the influence of the environment on the identified modal parameters.

A multidisciplinary approach to assess the health state of heritage structures: The case study of the Church of Monastery of Jerónimos in Lisbon

“…Dynamic identification tests were conducted in the main nave between 20th and 21st of April 2005 [1,7,14,16] using ambient excitations as operational conditions. Before proceeding with the Ambient Vibration Tests (AVTs), a preliminary numerical modal analysis with a simplified FE model was carried out to select and optimize sensors number and layout, and to choose sampling frequency and time window for the data acquisition.…”

“…Owing to the complexity of the structure and the difficulties in the modal parameters estimation, the FE model was manually tuned to the dynamic experimental results by using as a reference value for the correlation the modal frequency of the first vibration mode, i.e. the mode featuring the highest participation factor [7,16]. The updating parameters initially selected are the moduli of elasticity of columns and nave, and the boundary conditions of the columns.…”

“…Special regard is given to the environmental variability of the system, as subtle changes caused by damage in masonry structures may be often masked by changes due to varying ambient conditions [5][6]. Indeed, in the last decades, the analysis of the environmental effects on the system's behaviour has been regularly introduced in the common practice of structural health monitoring [5][6][7][8][9][10][11].…”

“…Although the structural behaviour of this monument has been already explored [7,12], new and fundamental aspects are addressed in the present work. The final scope of the paper is to give completeness to the diagnostic investigation of the Church of Jerónimos, merging the findings hereafter presented with the ones obtained in previous studies, in order to attain a deep comprehension of the global behaviour of this outstanding historical landmark for future design of adequate remedial measures.…”

Explaining operational modal analysis with data from an arch bridge

“…Now, it is relevant to point out some works with recent and interesting applications. In [47], it is described the ambient vibration test of the Humber Bridge, the largest suspension bridge in the United Kingdom; Siringoringo and Fujino [48] describe the processing of a database collected in a suspension bridge in Japan (Hakucho Bridge); in [49] several relevant applications on bridges and other special structures are presented; in [50], it is demonstrated the usefulness of ambient vibration tests in the context of the implementation of vibration control devices; Pakzad and Fences [51] present the results obtained with an ambient vibration test performed on the Golden Gate Bridge with wireless sensors; Carne and James III [52] describe the use of OMA in wind turbines testing; reference [53] characterizes the monitoring of historical masonry structures, taking profit from OMA.…”