Structural Interpretation of Data from Static and Dynamic Structural Health Monitoring of Monumental Buildings

Abstract

Structural Health Monitoring (SHM) has a crucial role in the diagnosis and conservation of historical buildings, which are typically characterized by articulated fabrics, constructed over decades using different materials and construction techniques. All these issues lead to very complex structural behaviour whose reliable assessment cannot disregard from a sound interpretation of data from SHM systems. SHM systems can be classified into (i) static systems, monitoring the long term time evolutions of specific quantities (such as amplitude of cracks, inclination of walls, relative distances, etc.) and (ii) dynamic systems, continuously monitoring the dynamic response (velocities, accelerations) in order to gather information upon overall dynamic properties such as natural frequencies, mode shapes and damping ratios. The recorded raw data need to be processed in order to distinguish eventual evolutionary trends from the seasonal and daily variations related to thermal effects. In the present work, a simple unified approach for data interpretation acquired from both static and dynamic SHM systems installed in historical buildings is presented. The approach is aimed at: (i) introducing reference quantities for interpretation of seasonal and daily variations, (ii) providing order of magnitudes of reference quantities and (iii) identifying eventual evolutionary trends which could be related to the presence of potential structural criticalities. The approach is illustrated referring to the “Two Towers” of Bologna.

An Assessment of the Structural Behaviour of the Garisenda Tower in Bologna Through Finite Element Modelling and Structural Health Monitoring

“…This system allows monitoring: movements of the main cracks, deformations of critical portions of masonry, inclination, strains along the steel ties (installed on the height of the tower to provide a lateral confinement to the masonry) and environmental parameter (such as temperature, wind speed). Additional details on the monitoring system are available in previous work developed by some of the authors [6], [7]. The results obtained from the analyses of the data recorded by the SHM system highlighted a slight evolutionary trend especially in relation to the inclination.…”

Identification Through Seismometric Measurements of Transients Propagating Inside the Asinelli and Garisenda Towers (Bologna, Italy), Implication on Structural Modeling and State of Health Monitoring

“…The knowledge of actual state of health the towers is a crucial issue in order to preserve these monuments. For this reason, at the beginning of the 2011 the Municipality decided to installed a static SHM systems in both the Towers [7], [8]. In addition, following the Emilia earthquakes (20th May 2012 and 29th May 2012, respectively 5.8 and 5.6 Mw), seismic monitoring experiments were commissioned to the Istituto Nazionale di Geofisica e Vulcanologia (INGV) in conjunction with the University of Bologna with the purpose of obtaining information on the dynamic behaviour of the Two Towers.…”

“…Also, from the spectral-analysis point of view, taking into account the wide frequency band covered by the natural vibration, it is possible to recognize the principal modal frequencies in a single step. Figure 4 and 5 show the average spectra computed over the entire monitoring period of 2013 for the three components of the top station for the Asinelli and Garisenda, respectively [7,8]. The first three fundamental flexural frequencies (indicated as F1, F2, F3 in the spectrum of figure 4a) of the Asinelli Tower fall within the range of 0.32-0.33 Hz, 1.3-1.5 Hz and 3.0-3.3 Hz.…”

Automated data analysis for static structural health monitoring of masonry heritage structures

“…The initial interpretation task then involves the identification of either a stationary condition or an evolutionary condition from the recorded data of each monitored response. Although this might appear simple in theory, in actual practice, it proves to be difficult, 18 given that features monitored for their sensitivity to damage are also sensitive to changes caused by environmental and operational conditions. In fact, it can even be said that this is a major issue prohibiting the extension of SHM technologies to structures in operation in the real world.…”

“…In order to provide a systematic way of dealing with seasonal changes, a simple method based on the evaluation of reference quantities was proposed. 18 In fact, this method can be considered as one aiming to solve the well-studied problem of identifying directionality from a time series, whereby directionality is defined as asymmetry in time. 32 As such, although it has been successfully applied to analyse data in a few heritage structures, 18,33 like many methods developed to detect directionality in other fields of study, 34 it cannot explicitly consider the effect of measured predictors on the response parameters.…”