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The presented research aimed at studying the dynamic behavior of Mallorca cathedral (Mallorca Island, Spain) under ambient sources of vibration and seismic events. The cathedral is one of the greatest built masonry structures worldwide. It is characterized for its audacious dimensions and slender structural members. Because of it, the study of its dynamic behavior is a clear concern. The cathedral dynamic properties were firstly identified using ambient vibration testing. Afterwards, a dynamic monitoring system was implemented to continuously measure, record, and wirelessly transfer the acceleration records without having to set up an activating threshold. This monitoring type was implemented because of the low seismic intensity of Mallorca Island with a basic ground acceleration of only 0.04 g according to the Spanish seismic standard. The continuous monitoring allowed for capturing some seismic events and some drops in the natural frequencies were noticed because of a breathing crack effect. Using both ambient vibration testing and continuous monitoring system, global modes could be more accurately identified than more local ones. The identification of the global modes was more attainable than in the case of more local ones. The temperature was a more influential environmental parameter than humidity and wind for all of the identified modes except for one more directly depended on wind.
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... Since both the long-term static behaviour and the time evolution of dynamic signatures are expected to be sensitive also to factors other than structural changes [10] and especially the temperature might affect the variation of structural parameters in historic masonry structures (see e.g. [11][12][13][14][15][16][17][18]), the indoor and outdoor environmental parameters (temperature and relative humidity) are extensively measured with the two-fold objective of establishing correlations with the structural parameters changes [11][12][13][14][15][16][17][18] and evaluating the risks for the preservation of the many artifacts present in the Cathedral [19]. ...
... Since both the long-term static behaviour and the time evolution of dynamic signatures are expected to be sensitive also to factors other than structural changes [10] and especially the temperature might affect the variation of structural parameters in historic masonry structures (see e.g. [11][12][13][14][15][16][17][18]), the indoor and outdoor environmental parameters (temperature and relative humidity) are extensively measured with the two-fold objective of establishing correlations with the structural parameters changes [11][12][13][14][15][16][17][18] and evaluating the risks for the preservation of the many artifacts present in the Cathedral [19]. ...
... It is worth noting that the monitoring system of the Milan Cathedral is -to the authors' knowledge -the largest ever installed in a Cultural Heritage monument and is the first truly aimed at assisting the condition-based structural maintenance. Previous implementations in historic monuments reported in the literature [11][12][13][14][15][16][17][18] involved the use of a limited number of sensing devices and were aimed at effectively addressing specific issues (such as controlling the structural effects of restoration processes [14] or monitoring the dynamic characteristics of historic buildings in seismic areas [12,15,16]). When a few accelerometers or seismometers are installed in the structure, resonant frequencies are often assumed as representative of the structural condition so that the detection of anomalies should include the removal of the temperature effects on identified frequencies [11][12][13][14][15][16][17][18]. ...
Article
The Milan Cathedral, whose main structures were erected between 1386 and 1813, is one of the largest masonry monuments ever built. Within the traditional collaboration between Politecnico di Milano and Veneranda Fabbrica del Duomo di Milano–the historic Institution established in 1387 and responsible for the preservation and development of the Cathedral–a structural monitoring system was recently designed and implemented with the two-fold objective of assisting the condition-based structural maintenance of the Cathedral and creating a large archive of experimental data, useful to improve the knowledge of the monument. The new monitoring system, fully computer based and with efficient transmission of the collected data, includes static and dynamic measurements. The static monitoring system consists of: (a) bi-axial tilt-meters installed at the top of selected piers and at 3 levels of the Main Spire; (b) vibrating wire extensometers mounted on the iron tie-rods which are characterized by the higher tensile stress; (c) temperature and humidity sensors for the measurement of internal and external environmental parameters. The dynamic monitoring is performed through seismometers (electro-dynamic velocity sensors) installed at the top of 14 selected piers and at 3 levels of the Main Spire. After a concise historic background on the Milan Cathedral and the description of the sensing devices installed in the church, the paper focuses on the results obtained during the first months of monitoring (since October 16th, 2018) and the lessons learned in view of the Structural Health Monitoring (SHM) of the monument.
... In addition, the indoor and outdoor environmental conditions (temperature and humidity) are extensively monitored with the twofold objective of evaluating the risks for the conservation of the main artefacts present in the cathedral [11] and establishing correlations with the structural parameters changes. The importance of the latter aspect for historic masonry structures has been shown in the long-term monitoring of towers [12,13], churches [14,15], cathedrals [16] and monumental buildings [17]: all those studies have highlighted that resonant frequencies [11][12][13][14][15][16][17], as well as static structural parameters [14,15,17], are significantly affected by changes in the environmental conditions. ...
... In addition, the indoor and outdoor environmental conditions (temperature and humidity) are extensively monitored with the twofold objective of evaluating the risks for the conservation of the main artefacts present in the cathedral [11] and establishing correlations with the structural parameters changes. The importance of the latter aspect for historic masonry structures has been shown in the long-term monitoring of towers [12,13], churches [14,15], cathedrals [16] and monumental buildings [17]: all those studies have highlighted that resonant frequencies [11][12][13][14][15][16][17], as well as static structural parameters [14,15,17], are significantly affected by changes in the environmental conditions. ...
... It is worth noting that the monitoring system installed in the Milan Cathedral represents a top example in the area of heritage constructions due to its complexity and extension, whereas the previous implementations reported in the literature involve the use of a very limited number of sensing devices, suitable to specific applications (such as controlling the structural effects of restoration processes [14] or monitoring the dynamic characteristics of towers [12,13] and buildings [16,17] in seismic areas). ...
Article
Full-text available
The traditional collaboration between Politecnico di Milano and Veneranda Fabbrica del Duomo di Milano—the historic institution established by Gian Galeazzo Visconti in 1387 and having in charge all operational aspects related to the Milan Cathedral since more than 600 years—recently focused on the design and installation of a structural monitoring system, with the objective of assisting the condition-based structural maintenance of the historic church through the continuous interrogation of sensors installed in the structure and the extraction from measured data of features which are representative of the current state of structural health. The new monitoring system of the Milan Cathedral includes different types of measurements and sensors: quasi-static acquisition of strain in selected tie-rods and biaxial tilt of selected piers and the main spire, monitoring of inner and outer environmental parameters and dynamic measurement of the velocity response at the top of 14 piers and at 3 levels of the main spire. After a concise description of the historic church and of the monitoring system, the paper focuses on the dynamic characteristics of the Milan Cathedral, their evolution during the first months of monitoring (since October 16th, 2018) and the lessons learned in view of the structural health monitoring of the monument. The presented results from the vibration monitoring highlight that: (a) 8 global modes of vibration are automatically detected in the frequency range 1.0–5.0 Hz; (b) the resonant frequencies exhibit a distinctive trend of variation, which is mainly driven by temperature; (c) the mode shapes of the cathedral do not show appreciable fluctuations associated with the environmental effects.
... Such techniques can now be applied to provide information on a wide variety of aspects that are key to an accurate diagnosis. Applications exist to obtain more accurate representations of the geometry and damage [2][3][4][5][6][7][8], to estimate material properties [9][10][11][12][13][14][15][16][17], to characterise material quality and variability [17][18][19][20][21][22], to evaluate actual loading and boundary conditions [17,[23][24][25][26], and even to monitor the structural response [27][28][29][30][31][32][33][34][35]. Similarly, there is a considerable amount of literature on numerical modelling [36][37][38][39][40][41][42][43][44][45][46][47] and other structural analysis tools [48][49][50][51][52] that can be used to provide vital information for diagnosis and for accurately assessing the damage vulnera- 30 bility of masonry heritage structures. ...
... Having been built over a period of 300 years, the cathedral has a very complex structural scheme consisting of the interaction of several different parts. It has been the subject of numerous 960 studies and scientific investigations of relevance for characterising damage risk and has in part been chosen as a case study because both the details and conclusions of these studies are well reported in literature [28,35,48,[94][95][96][97][98][99][100][101]. In addition, data collected from a static SHM system over a period of 5 years from 2003 to 2008 had already been processed using the automated data analysis procedure presented in [35]. ...
... Various structural analysis methods have also been applied for the diagnosis and safety evaluation of the structure, including graphic statics analyses to 975 evaluate the stability of a transverse bay [48,101], kinematic analyses of macro elements to evaluate the seismic capacity (limit analysis) [101], and several sophisticated finite element modelling (FEM) approaches to assess the vulnerability to both progressive collapse and earthquakes [48,[98][99][100]. In addition to the previously mentioned static monitoring system, two different dynamic SHM systems have been installed in the structure, one in 2005 [96] and the other in 2010 [28]. Several investigations have also been carried out 980 to better understand the material quality and variability in several parts of the structure. ...
Article
Full-text available
Experts responsible for the safety evaluation of unique masonry heritage structures usually need to weigh information from various diagnosis activities before deciding the best course of action for preservation. Typical sources of valuable information are historical and in situ surveys and inspections, minor and non-destructive testing, structural health monitoring, and structural analysis, among others. Due to the complexity of the problem and singular aspects of monuments, these decisions are challenging and often made solely on the basis of expert judgement. A systematic risk assessment procedure is proposed involving the computation of two indices to facilitate the decision-making process: an index related to the estimated risk of damage, and another to the uncertainty behind this estimation. Results from applying the procedure to several case studies are provided to demonstrate its usefulness.
... All of the octagonal columns have a circumscribed diameter of 1.7 m except those of the first three bays from the choir that have a slightly lesser value of 1.6 m. More information on the cathedral can be found at Elyamani et al., 2017a;Gonzalez et al., 2008;Elyamani et al., 2017b;Pela et al., 2014;Elyamani, 2015;Caselles et al., 2015;Elyamani et al., 2012;Roca et al., 2013). (c) (d) ...
... The natural frequencies and modes shapes were used to update the numerical model of the cathedral which was then used in the seismic analysis of it (Elyamani et al., 2017a). A brief about AVT is given here and full details can be consulted at (Elyamani et al., 2017b;Elyamani, 2015). ...
... The use of AVT was followed by a continuous dynamic monitoring system. A brief is given here and more details can be referred to at (Elyamani et al., 2017b;Elyamani, 2015). The system was composed of a digitizer, a Data Acquisition system (DAQ), a Global Positioning System (GPS) antenna, an internet router and the three tri-axial accelerometers previously used in the dynamic identification tests, Figure 4. ...
Article
Full-text available
An integrated investigation of engineering archaeometry was carried out using dynamic identification, dynamic monitoring and Infra-Red (IR) thermography for the study of the dynamic behavior of Mallorca cathedral in Spain. The cathedral is a large historical masonry structure built during 14-16th c. Dynamic identification and monitoring allowed the capturing of eight natural frequencies of the cathedral. IR thermography was used as a complementary inspection technique in the context of a continuous monitoring. Usually, IR thermography is used punctually for the inspection of a part of an inspected structure. Here an alternative was tried as the IR camera was installed for two two-weeks periods in the winter and in the summer of 2011 to monitor the stone surface temperature of a large portion of the cathedral. The correlation between the cathedral natural frequencies and the stone surface temperature of some selected structural elements was investigated and compared with the correlation with the external and the internal temperatures. It was found that the correlation with stone surface temperature was lower than that with external temperature. The study allowed a better understanding of the influence of temperature changes on the structure's dynamic behavior.
... Currently, almost all kind of the structural elements (walls, columns, vaults, arches) are cracked. Many studies have already pointed out the reasons of such cracking including previous earthquakes, deterioration of materials, low quality of construction materials, among others (Martinez et al. 2007;Pérez-Gracia et al. 2009;Pérez-Gracia et al. 2013;Caselles et al., 2012;Caselles et al., 2015;Elyamani, 2015;Elyamani et al., 2017a and2017b). A dynamic monitoring system was installed in the cathedral for about 15 months during 2010-2012. ...
... The post processing of the monitoring system showed the high correlation between air temperature changes (from -2ºC and 40ºC) and some modal frequencies. As well, some decreases in the natural frequencies were observed under the effect of some seismic events occurred near to Mallorca Island (north of Algeria and Italy) (Elyamani et al., 2017a). These changes were attributed to the opening/closing process of the distributed cracks in the structural elements of the cathedral. ...
Conference Paper
Full-text available
For preserving existing structures to the extent possible, vibration-based damage detection techniques are gaining more attention. In specific, tracking the changes in a structure's natural frequencies employing the Principal Component Analysis (PCA) seems to be a promising technique. This paper presents an ongoing research for developing an approach for damage detection based on identifying the natural frequencies of the structure (via dynamic identification or monitoring) followed by applying PCA on the temporal variation of the identified natural frequencies. The processing of the dynamic monitoring data was carried out using a proposed semiautomatic algorithm able to identify and track the natural frequencies of the monitored structures and their changes over time. The algorithm was applied on one historical structure and two modern ones. PCA will to be carried out. The so far developed approach as a whole was applied on a steel structure model tested in lab. It was subjected to dynamic identification tests with and without damage. It was found that PCA applied to frequency variation seems to be a possible tool to know damages in structures. Nevertheless, the simplified point of view correlating directly the number of PCs with the damage importance seems to be not accurate. First results seem to indicate that the variance percentage explained by each of the principal components could be correlated with the kind of damages and the shake used to excite the structure.
... However, the estimated frequency shifts did not exceed the assumed confidence limits meaning that only minor damage took place during the earthquake. Elyamani et al. (2017) marginally commented on the response of the Mallorca cathedral (Mallorca Island, Spain) to a few recorded earthquakes. In some cases, the spectrograms showed a low decrease in the natural frequency values ( � 3%). ...
... The frequency drop parallels with the findings by (Azzara et al. 2018;Elyamani et al. 2017;Gentile, Guidobaldi, and Saisi 2016;Masciotta et al. 2016;Ubertini et al. 2018), who observed a small decrease of the natural frequency of masonry structures during lowintensity seismic events. In the current case, the identification carried out before and after the seismic event yields the same modal parameters, likely confirming that no minor damages occurred during the event. ...
Article
Full-text available
The seismic response of masonry monumental structures is a debated matter. In this paper, the authors compare the dynamic response of the Santa Maria di Collemaggio basilica under low-intensity earthquakes to the dynamic response under operational conditions. A permanent number of accelerometers records the dynamics of the Santa Maria di Collemaggio basilica under both operational and seismic excitation. It is questioned whether the earthquake intensity and the ambient parameters affect the modal parameters. The Least-Squares Complex Exponential (LSCE) method leads to the FRF function estimation. The stable frequencies identify the linear modal parameters which are likely to reproduce the seismic response. The authors endeavour to discuss whether the detected variations of the modal parameters are due to possible structural or material non-linearities. A time-frequency analysis confirms the results of the linear identification method. Further, the estimate of the dynamic amplification factors gives a glance over the global response by evidencing the possible existence of a macro-element response pattern.
... 41.2. Full details can be consulted at [55]: here a brief is given with a focus on the methods followed. The initial inspection revealed that the points above the central and the lateral naves' vaults would be the most appropriate to accommodate the accelerometers. ...
... During the period of the dynamic monitoring, some earthquakes were captured, and their effect was noticed in terms of a reduction of the natural frequencies of some modes. More details are available at [55]. ...
... Vibration-based structural monitoring is being increasingly used for the structural evaluation of historical constructions, such as bell towers (Foti et al. 2012;Gentile, Saisi, and Cabboi 2015;Lourenço 2006;Saisi, Gentile, and Ruccolo 2018), stone masonry churches (Elyamani et al. 2017;Lorenzoni et al. 2018;Ramos et al. 2013Ramos et al. , 2010 and buildings (De Stefano, Matta, and Clemente 2016;Lorenzoni et al. 2016;Noh and Russo 2017), because it allows the collection of realtime data that is used for assessing the structural vulnerability (Masciotta et al. 2016), for quantifying the strengthening needs (Masciotta, Ramos, and Lourenço 2017), and for performing real-time damage detection (Fan and Qiao 2011). The structural health assessment of existing buildings is a challenging task because of the influence of environmental conditions, which can provoke variations in the boundary conditions (Reynders and Roeck 2009;Ubertini, Gentile, and Materazzi 2013), in the system stiffness (Maeck, Peeters, and De Roeck 2001) and others, complicating the accurate identification of structural anomalies (Gentile, Guidobaldi, and Saisi 2016;Peeters and De Roeck 2001;Ubertini et al. 2017;Zhou and Yi 2014). ...
... Different authors have reported a strong influence between the variation of the ambient temperature and the variation of the natural frequencies (Cabboi, Gentile, and Saisi 2017;Kita, Cavalagli, and Ubertini 2019;Magalhães, Cunha, and Caetano 2012;Saisi, Gentile, and Guidobaldi 2015;Sohn 2007;Zonno et al. 2019a). Some studies reported positive correlations between temperature and natural frequencies for slender fired clay brick masonry towers (Gentile, Guidobaldi, and Saisi 2016;Magalhães, Cunha, and Caetano 2012;Saisi, Gentile, and Guidobaldi 2015;Sohn 2007) and for stiffer masonry structures (Elyamani et al. 2017;Masciotta, Ramos, and Lourenço 2017;Masciotta et al. 2016), which is induced by the closing effect of micro-cracks in the masonry system originated by the increase of ambient temperature. On the contrary, Kita et al. (Kita, Cavalagli, and Ubertini 2019) found negative correlations between natural frequencies and ambient temperature in the case of a complex stone masonry palace, concluding that the presence of metallic reinforcements in the building caused the increase of global structural stiffness in the case of lower temperatures. ...
Article
This paper presents the application of long-term environmental and structural remote monitoring in two emblematic 16th-century adobe churches located in southern Peru. The paper starts by presenting details of the planning and installation processes of the monitoring systems and continues with a detailed discussion of the results of almost two years of continuous monitoring. As expected, due to the large thermal inertia of the adobe systems and size of the buildings, the results of the environmental monitoring indicated a non-uniform distribution of temperature and relative humidity inside the buildings, and an important attenuation of the internal conditions in comparison with the external ones. On the other hand, the structural monitoring results evidenced an annual cyclical behavior of the natural frequencies with an apparent correspondence with the changes in environmental conditions due to seasonal influences. The correlation of ambient conditions and structural parameters confirmed the high affinity between relative humidity measurements and natural frequencies when hourly fluctuations were removed from the measurements. An important novelty is the affinity of structural dynamic properties and a single environmental variable, the absolute humidity, was also evidenced since high determination coefficients were obtained when it was compared with the identified natural frequencies.
... It should be noticed that, unlike previous experiences of long-term monitoring large churches (see e.g. Potenza et al. 2015, Masciotta et al. 2016, Elyamani et al. 2017, Masciotta et al. 2017, Zonno et al. 2019, monumental buildings (Kita et al. 2019) and towers (Gentile et al. 2016, Cabboi et al. 2017b, Ubertini et al. 2018, where a limited number of sensing devices was used, the monitoring system implemented in the Milan Cathedral includes a relatively large number of sensors for measuring both static (15 bi-axial tiltmeters and 12 vibrating wire extensometers) and dynamic parameters (36 uni-axial seismometers); in addition, the indoor and outdoor environmental conditions are extensively monitored. In designing the monitoring system of the Milan Cathedral (Gentile et al. 2019), utmost attention has been paid to the Main Spire (Fig. 2), which already underwent several restoration works (Nava 1845, Zacchi 1941, despite it is one the youngest sub-structures of the cathedral. ...
... (a) The level of ambient excitation allows the identification and tracking of 9 local modes in the range 1-7 Hz with high occurrence; (b) The identification rate is higher for modes S1-S3 and S7-S9, ranging from 91.3% for S9 to 99.4% for S7, whereas it decreases to 56.1% for mode S5; (c) All identified frequencies seem to evolve in time according to regular patterns mainly driven by the temperature and tend to increase with decreased temperature, with this distinctive trend being especially clear for modes S1-S2 and S5-S9; (d) The negative dependence of natural frequencies on temperature is a distinctive behavior of the Main Spire and of the Milan Cathedral (Gentile et al. 2019), with this trend being very different from what generally reported in the long-term studies on masonry structures, either towers (Gentile et al. 2016, Cabboi et al. 2017b, Ubertini et al. 2018, Azzara et al. 2018 or churches (Masciotta et al. 2016, Elyamani et al. 2017, Masciotta et al. 2017). Table 3 summarizes the correlation coefficients between the different natural frequencies in the investigated time span and highlights that the identified frequencies are characterized by correlation coefficients generally higher than 0.6, with the exception of the frequencies of modes S5-S6, which are less correlated with the others. ...
Chapter
One of the most remarkable structural elements characterizing the Milan Cathedral is its main spire, reaching the height of about 108 m and supporting the statue of the Virgin Mary. The Main Spire, built in Candoglia marble and completed in 1762, is about 40 m high and stands on the tiburio of the cathedral (i.e., the prismatic structure with octagonal base built around the main dome). The spire consists of a central column which is connected through a spiral staircase to 8 perimeter columns, with each column being stiffened by a flying buttress. The structural arrangement is completed by (i) metallic clamps and dowels, connecting the marble blocks, and (ii) metallic rods, connecting the perimeter columns to the central core.
... In 2010, AVT was repeated again (Elyamani et al., 2017a;Elyamani, 2015;Caselles et al., 2012;Bettoni, 2011). Three tri-axial force balance accelerometers were used. ...
... (a) First numerical mode shape, and (b) second experimental mode shape (Elyamani et al., 2017a). (a) Second numerical mode shape, and (b) fourth experimental mode shape(Elyamani et al., 2017a). ...
Article
Full-text available
Mallorca cathedral is one of the largest ever built cathedrals in the world. When compared with all other Gothic cathedrals in the world, it is found that its columns have the highest slenderness ratio, its main nave span is the second longest after Girona cathedral, and its main nave is the third highest after those of Beauvais and Milan cathedrals. The preservation of the cathedral was always of concern due to its audacious dimensions and slender structural members. About one century ago, a pioneering structural assessment was carried out by Rubió. Since then, and up to date, a relevant number of studies have been carried out on this cathedral and covered many aspects such as the history of construction, the characterization of the construction materials, the seismic assessment, the static and the dynamic monitoring, and the investigation of the foundation soil, among others. The objective of this article is to review these studies making focus on their main conclusions that are relevant for future studies on the cathedral and other similar historical structures.
... In general, monitoring strategies to be applied can be categorised as static or dynamic. Dynamic monitoring is oriented to the characterisation and control of dynamic properties such as natural frequencies, mode shapes and damping ratios [2][3][4][5][6][7] . Static monitoring is aimed at the continuous measurement of slow-varying parameters over a long period 8 . ...
... Although this means that the noise and the dynamics of the system cannot be modelled independently, the simplicity of the scheme creates no stability problems in optimal predictors and allows unbiased estimates of the parameters by means of least squares. However, it is crucial to remove the mean from both the response and predictor data before carrying out system identification to avoid an offset term in Equation (2). In fact, it is good practice to normalise the input and output data for this system identification task 41 . ...
Article
Full-text available
Masonry heritage structures are often affected by slow irreversible deterioration mechanisms that can jeopardise structural stability in the foreseeable future. Static structural health monitoring (SHM), aimed at the continuous measurement of key slow‐varying parameters, has the potential to identify such mechanisms at a very early stage. This can greatly facilitate the implementation of adequate preventive and remedial measures, which can be critical to ensure that such structures are preserved for generations to come. However, because monitored parameters usually experience reversible seasonal variations of the same order of magnitude as changes caused by active mechanisms, identification of the latter is often a difficult task. This paper presents a fully integrated automated data analysis procedure for complete static SHM systems utilising dynamic linear regression models to filter out the effects caused by environmental variations. The method does not only produce estimated evolution rates but also classifies monitored responses in predefined evolution states. The procedure has successfully been used to identify vulnerable areas in two important medieval heritage structures in Spain, namely, the cathedral of Mallorca and the church of the monastery of Sant Cugat.
... The model included 149248 nodes and 491851 elements with 490789 degrees of freedom. The model was updated based on in-situ dynamic identification tests (Elyamani et al., 2017a(Elyamani et al., , 2017b. The nonlinear tensile behavior of the masonry was modeled using smeared cracking (multi-directional fixed crack model) and the compressive behavior was modeled using isotropic plastic Drucker-Prager model. ...
Article
Full-text available
The paper discusses the seismic assessment of Mallorca cathedral in Spain. This cathedral is an audacious Gothic structure built on the island of Mallorca during 14th-16th centuries, characterized by its large dimensions and slender structural members. For that purpose, different analysis methods were used. A 3D Finite Element (FE) model of the cathedral was created and then updated based on in-situ dynamic identification tests. Nonlinear static (pushover) analysis was firstly carried out applying the seismic loads in the longitudinal and transversal directions of the cathedral considering both positive and negative signs. The pushover results were compared with the results of the kinematic limit analysis as a way to cross check the seismic safety assessment. Although for such a large historical structure, the nonlinear time-history (dynamic) analysis requires a very high computer effort, an attempt to perform this type of advanced analysis was carried out. KEYWORDS: Seismic assessment, Mallorca cathedral, pushover analysis, non-linear dynamic analysis, limit analysis 42 A. ELYAMANI et al.
... A detailed characterization of the environmental effects is crucial for improving knowledge in this field and for defining suitable damage-sensitive features. Several authors reported significant changes in natural frequencies caused by temperature variation [10][11][12][35][36][37][38][39][40], and in particular, presented positive correlations for slender masonry [12,37] towers and for stiffer masonry structures [21,41,42]. This behavior was explained as the effect of thermal expansion in the masonry determining the closing of microcracks or discontinuities in the masonry structure, compacting the materials and inducing a temporal increase of the global stiffness. ...
Article
Through long-term monitoring, modal parameters identified in-situ can provide important information about the safety state of civil buildings and infrastructures. Unfortunately, structures are subjected to changing environmental conditions that can mask variations in the dynamic properties caused by damage and, therefore, lead to an incorrect condition assessment. The quantification of the influence of environmental conditions on modal parameters is a crucial step to eliminate their interference in a safety evaluation. Under current state-of-the-art considerations, this step is still an open challenge because environmental variables are time-dependent non-uniform quantities that have different influences on structural systems depending on the predominant material. In this paper, the effects of ambient temperature and humidity on the dynamic properties of earthen constructions are investigated using laboratory tests. A dynamic monitoring system was successfully implemented on adobe walls of different thicknesses to examine the influence of seasonal and daily variations of temperature and humidity. Three 1:1 scale adobe masonry walls were built and exposed to ambient conditions for 240 days. Temperature and humidity variations on the exterior, as well as in the inner walls, were continuously recorded together with the dynamic behavior using ambient vibration. The results provide useful insights on the influence of thermohygrometric parameters on the dynamic properties of adobe systems. The seasonal results indicate unclear correlations of ambient parameters and environmental variables. On the other hand, at a daily scale, the results indicate the existence of a clear relationship between inner measurements and dynamic properties. Moreover, the results indicate the existence of a delayed effect of external ambient parameters in the dynamic behavior of earthen systems.
... Five hammer blows were applied in correspondence of each instrumented cross section ( Figure 9); the time interval between two subsequent blows was set approximately equal to 60 sec, so that data records of about 900 sec were acquired. Since the dynamic characteristics of both tie-rods (Rainieri and Fabbrocino 2015) and masonry structures (see, e.g., Elyamani et al. 2016;Saisi, Gentile, and Guidobaldi 2015) have proved to depend on temperature, the inner ambient temperature was measured during the tests, whereas the outer air temperature was referred to the records of a neighbouring weather station (Osservatorio di Brera). ...
Article
One of the distinctive characteristics of the Milan Cathedral, built over a period of more than 400 years, is the presence of iron ties under the vaults of all 5 naves. Those tension bars date back to the age of construction and still have an important role in supporting the lateral thrust exerted by vaults and arches. After the recent failure (November 2011) of one tie-rod, an extensive research program was carried out to assess the structural condition of all iron ties. The investigation included the characterization of the metallic material, the direct inspection of the ties and the evaluation of the axial force in the structural elements through dynamic testing and system identification. After a concise description of the Milan Cathedral, this article presents the adopted methodology for the dynamic assessment of the tie-rods in the Milan Cathedral and the main results of the investigation, in terms of fundamental frequencies and axial forces in the metallic elements. Subsequently, the splitting of the first resonant frequency observed on two ties is presented: this anomalous phenomenon (which is occasionally reported in the literature as associated to the response of cracked reinforced concrete beams) is addressed and its correlation with the occurrence of local damage is discussed.
... In the case of slender masonry towers, several authors reported significant changes in natural frequencies caused by temperature fluctuations [10,11,[13][14][15][16][34][35][36][37], often finding an increase in natural frequencies with increasing temperature, conceivably explained as the effect of thermal expansion in the masonry determining closing of superficial cracks or micro-cracks in mortar layers and minor masonry discontinuities (temporary ''compacting'' of materials induces a temporary increase in structural stiffness) [14,15,34,37]. Similar positive correlations between modal frequencies and temperature were also observed in the case of stiffer masonry structures, such as churches and/or cathedrals [38][39][40]. It is important to notice that for structures made of different construction materials, such as modern RC structures, negative frequency-temperature correlations were observed. ...
Article
In recent years, the development of long-term structural health monitoring systems for preventive conservation of historic monumental buildings is receiving a growing trend of scientific interest. Nevertheless, the damage detection effectiveness of these systems is still debated, especially in respect to complex masonry palaces where both local and global failure mechanisms can be activated, whereby the majority of the documented successful applications are limited to masonry towers. In particular, one major issue that needs to be solved in order to derive damage sensitive features is associated to the removal of the effects of changes in environmental conditions and, primarily, of ambient temperature, from static and dynamic signatures. This paper aims to contribute to improving knowledge in this field, by investigating temperature effects on static and dynamic response of an iconic Italian monumental palace: the Consoli Palace in Gubbio. With the purpose of early detecting earthquake-induced damages, as well as damages caused by material degradation associated to awkward environmental conditions, a simple low-cost mixed static and dynamic long-term structural health monitoring system has been installed on the Palace by the authors in July 2017. After discussing surveys, ambient vibration tests, diagnostic investigations, numerical modeling and model calibration of the Palace, the analysis of the first year of monitoring data is presented. This analysis shows that, differently from what observed in other literature works on historic masonry towers, the natural frequencies of the Palace show a marked and sometimes non-linear decreasing trend with increasing ambient temperature, that can be effectively removed through linear statistical filtering provided that dynamic regression models, using past values of predictors, are used. On the other side, the evolution of the amplitudes of two major cracks monitored within the building also shows a marked linear decreasing trend with increasing ambient temperature. These results are meaningful towards the use of monitoring data for assessing the initial health conditions of a structure, as well as in a damage detection perspective.
... [8,9] Therefore, it is difficult to predicate the type and the location of deformations of this type of buildings that made some researchers to recommend, for an effective structural health monitoring, distributing redundant sensors. [10] Other researchers have proposed a numerical modal analysis using finite elements to choose the appropriate locations for monitoring sensors, [11,12] or employing digital photogrammetry and terrestrial laser scanning to obtain the finite element model. [9] Consequently, the required technique should have ability to detect unpredictable deformations. ...
Article
Numerous different techniques and instruments can be used for structural monitoring with different requirements producing different results. For instance, some techniques need to use embedded sensors inside the building, such as geotechnical sensors. However, this method cannot be used for historic and heritage buildings. Other methods can offer high quality, but with a low point density and require fixed stations and targets, such as total stations. In such a case, the location of deformation tends to be known, such as dams, bridges, high-rise buildings, and so forth. Nevertheless, this is not the case for historic and heritage buildings where each block could be subject to deformation. The challenge in such a case is to detect the deformation without any previous knowledge. The aim of this research is to develop a new approach to detect and localise unpredictable deformation. It is based on terrestrial laser scanner measurements and generalised Procrustes analysis techniques to determine deformation vectors, although boxing structure and F-tests are used to detect and localise deformation. In summary, after applying this approach, the whole concerned building is represented as parts, for each of them, the displacement vector and deformation probability are estimated. Validation experiments have shown the capability of the proposed method to detect and localise deformation with magnitude less than noise level in simulated data and of subcentimetre level for ranges up to 10 m in real scan data. Finally, the new approach has been applied to an English Historic site, Bellmanpark Limeklins.
... The correct interpretation of vibration-based SHM results may lead to understand the health status of the studied systems, as well as the detection of issues related to materials aging and degradation [15]. The literature reports several applications of vibration-based SHM of heritage buildings which were mainly aimed at assessing the structural performance and tracking its evolution in time [16,17]. This type of applications has been successfully implemented for the extraction of damage sensitive features [18,19], evaluation and elimination of environmental influences [20,21], and post-earthquake structural assessment [22,23]. ...
Article
Full-text available
Historical buildings demand constant surveying because anthropogenic (e.g., use, pollution or traffic vibration) and natural or environmental hazards (e.g., environmental changes or earthquakes) can endanger their existence and safety. Particularly, in the Andean region of South America, earthen historical constructions require special attention and investigation due to the high seismic hazard of the area next to the Pacific coast. Structural Health Monitoring (SHM) can provide useful, real-time information on the condition of these buildings. In SHM, the implementation of automatic tools for feature extraction of modal parameters is a crucial step. This paper proposes a methodology for the automatic identification of the structural modal parameters. An innovative and multi-stage approach for the automatic dynamic monitoring is presented. This approach uses the Data-Driven Stochastic Subspace Identification method complemented by hierarchical clustering for automatic detection of the modal parameters, as well as an adaptive modal tracking procedure for providing a clear visualization of long-term monitoring results. The proposed methodology is first validated in data acquired in an emblematic sixteenth century historical building: the monastery of Jeronimos in Portugal. After proving its efficiency, the algorithm is used to process almost 5000 events containing data acquired in the church of Andahuaylillas, a sixteenth century adobe building located in Cusco, Peru. The results in these cases demonstrate that accurate estimation of predominant modal parameters is possible in those complex structures even if relatively few sensors are installed.
... Nevertheless, given the paramount need of a non-destructive approach when dealing with CH buildings, Ambient Vibration Tests (AVT) can be considered an effective tool for identifying the modal parameters [12], being the excitation input represented only by wind, traffic and human activities, and the estimated natural frequencies and mode shapes can be used for advanced assessment of structural integrity under operative conditions, and can also provide a prompt baseline for further damage detection. Although AVTs have proven to be suitable techniques for modal identification of CH buildings [13][14][15][16] and specifically of churches [17][18][19][20] and towers [21][22][23][24][25][26], this methodology is still not extensively applied. Nonetheless, recent research has confirmed that the potential of this methodology can be further investigated [27]. ...
Conference Paper
Full-text available
Churches are an important part of New Zealand's architectural heritage, and the extensive damage observed in stone and clay brick unreinforced masonry churches after the 2010-2011 Canterbury earthquakes has highlighted the need to appropriately describe their dynamic characteristics. Dealing with historical structures, characterized by a high level of uncertainty affecting both material properties and structural schemes, and given the paramount need of non-destructive investigation techniques, ambient vibration tests can be considered an effective tool. A test campaign was conducted on two churches located in Auckland and deemed to be representative of the New Zealand church portfolio. The structures were instrumented with low-cost tri-axial standalone accelerometer sensors based on Micro Elec-tro-Mechanical Systems (MEMS) technology. Despite such instrumentation being commonly used on more flexible structures and/or under higher service loads (such as the normal traffic on bridges), this technology potentially represents an affordable solution to provide information about the fundamental period of vibration of macro-elements of churches and bell-towers. The advantages and limitations of the adopted sensing technology, when applied to historic buildings exhibiting low response to ambient excitation, are discussed in the paper, based on the analysis of data collected.
... The seismic vulnerability of historic masonry structures, and its reduction caused by material degradation, is a primary concern in Mediterranean countries, where recent earthquakes caused major damages to this type of buildings [24][25][26][27][28][29][30][31]. Several studies investigated damaging processes affecting historical structures, including advanced diagnostic and monitoring methods [32][33][34][35][36][37][38], but often missed the contribution of climate forcing, or at most considered the environmental effects only for their removal from the monitoring data [39,40]. On the contrary, a structural damage affecting masonry, typically in the form of cracks passing through mortar layers and stone or brick elements, locally results in a less protected material that is more exposed to awkward environmental conditions and, therefore, to degradation phenomena. ...
Article
Resilience of new and existing buildings to climate change is a key research issue. Climate change-related phenomena can considerably affect buildings mechanical and thermal-energy response by contributing to materials degradation and structural safety. Such an impact is even further exacerbated in historical constructions, more vulnerable to such events due to their ancient structure if compared to recent designs. The purpose of this paper is to propose an innovative, integrated, multidisciplinary methodology for assessing construction materials’ degradation in historic masonry buildings and its potential future evolution, providing a risk mapping accounting for interactions between climate change effects and structural damage. Such a replicable approach consists in (i) preliminary site inspections, (ii) damage and degradation surveys, (iii) development and calibration of numerical models predicting structural-thermal response and (iv) prediction of materials degradation accounting for future climate conditions and potential worsening of structural damage. The final output of the procedure is a hierarchical mapping of regions with different degradation severities, by identifying those where a specific type of degradation or damage insists but are likely stable and those where they are expected to get worse due to changes in future climate conditions or to a negative interaction between degradation and damage. The presented approach is applied to an iconic Italian monumental building, the Consoli Palace in Gubbio, where future climate scenarios up to 2080 are simulated according to the IPCC climate change predictions. Results highlight that thermal-energy and structural aspects need to be jointly considered in the preservation of surface materials of historic buildings exposed to climate change severity.
... There are many successful cases in the literature in which structural analysis have been used as an efficient tool in the study of historical structures. The structural safety of the cathedral of Mallorca, one of the largest built cathedrals worldwide, was successfully assessed under seismic loads using a FE model (Elyamani et al., 2017a, Elyamani et al., 2017b, , Elyamani, 2015. Elyamani (2009Elyamani ( , 2016 studied the structural behavior of the spire of Barcelona cathedral under wind and earthquake loads using a FE model for the spire. ...
Article
Full-text available
The Palace of Baron Empain in Cairo is a unique architectural masterpiece of its kind. Edward Empain, a rich Belgian, built it in 1911 influenced by the architecture of the famous Cambodian temple of Angkor Wat. The palace is composed of three floors (basement, ground and first) and a roof, it is surrounded by a garden from all sides. It suffered from neglect for decades, and recently appeared initiatives for its restoration and re-use. This paper aims to provide a proposal for the re-use of the palace. For this purpose, the palace was visually inspected and the signs of damage were documentated and explained. A re-use proposal was developed in which the ground floor is re-used as a small museum after being furnished on the historical style. The first floor is re-used as a museum and/or a motel. The roof is re-used in holding cultural seminars, and as a place for distinctive imaging types. The palace garden is to be re-used similar to its historical usage as an open space for celebrations and parties. The basement is re-used as a service floor for the visitors. To support this re-use proposal, a 3D numerical model of the palace was created and the new expected loads were applied on it. It was found that the palace's walls and foundations can sustain the new loads. The slabs were found to be unable to sustain the new loads at certain places and further investigation and analysis is needed to judge its actual capacity.
... The authors believe that their research presents a number of optimum regions suitable for sensor placement for similar Gothic cathedrals, and the use of these recommended locations is anticipated to reduce the neces- In addition to the previously discussed case studies of dynamic testing of historic structures, some additional cases can be mentioned. These include the AVT carried on a historical basilica in Rome (Pau and Vestroni, 2013); a fortress in L'Aquila damaged by Abruzzo 2009 earthquake (Lorenzoni, 2013); a church in Portugal (Alaboz, 2009); a large cathedral in Spain (Caselles et al., 2012;Elyamani et al., 2017a and2017b); and many historic buildings in Cyprus including a Gothic cathedral, a Byzantine church, ruins of a church and some schools (Votsis et al., 2013;Votsis et al., 2012;Lourenço et al., 2012;Chrysostomou et al., 2013). Finally, it is worthy to comment that the dynamic tests (also the identification process and the numerical model updating) are easier to carry out on some types of masonry historic structures. ...
Article
Full-text available
Assessment of seismic safety of historical structures is a challenging task because the information available about the assessed structure is usually limited. Therefore, it is often necessary to exploit a number of integrated investigation activities to increase the level of knowledge about the historical structure under consideration. Thus, in the case of any need for providing the structure with strengthening intervention, this intervention will be a minimal and any unnecessary strengthening operations will be avoided. This paper presents a literature review carried out to cover the current state-of-the-art of a number of investigation activities carried out integrally for the seismic safety assessment of historical structures. It is presented in two parts. In this first part, the covered topic is the dynamic investigation of historical structures which includes the dynamic identification tests, the dynamic monitoring, and the modal parameters identification methods with the classical and the advanced techniques like the peak picking and the stochastic subspace identification.
... [18] These effects have been eliminated by a drainage system put in place recently. [19] Of course, more examples could be cited, [20][21][22] but those mentioned before are sufficient to emphasize the importance of having an adequate monitoring strategy that allows to successfully investigate the long-term behavior and the correlation between such behavior and the environmental changes induced by anthropogenic causes or natural events. ...
Article
This paper focuses on the integration of geodetic monitoring and geotechnical modeling for the analyses of subsidence induced settlements in historic structures. The aim is the assessment of the behavior over time of the monuments, with particular attention to differential settlements, in order to evaluate the potential risk scenarios in a preventive strategy. The methodology is applied to the UNESCO site of Modena where the Cathedral and the Ghirlandina Tower are characterized by strong visible deformations due to a complex construction history, the peculiar subsoil conditions and the effects of both natural and man induced subsidence. A 3D finite element numerical model has been developed taking into account the soil characteristics gained by laboratory and in situ tests. The model takes into account the influence of previously existing structures, as well as the subsidence phenomena and provides a settlements profile in agreement with the real dataset collected by high-precision leveling. The geodetic monitoring, carried out since 1984, allows to optimize and then to validate the numerical model giving the Conservation Authority a useful tool to manage the safety of the heritage.
... More recently, several SHM applications in which excellent results have been achieved by using a limited number of sensors have been proposed. A non-exhaustive list of these applications includes: the monitoring of the stress-ribbon footbridge in the Faculty of Engineering of the University of Porto (Portugal) [3] in which structural changes are automatically detected by an efficient statistical treatment of the acquired data; the system implemented in the Gabbia tower in Mantua (Italy) where a vibration-based strategy for dynamic monitoring of historic towers has been applied [4]; and the case study of the Mallorca cathedral (Spain), one of the world's largest masonry structure, in which four identification methods of dynamic properties have been used [5]. ...
Article
The term Structural Health Monitoring (SHM) usually refers to the process of implementing a damage detection strategy for aerospace, civil or mechanical engineering infrastructures. Under an extreme event, such as an earthquake or unanticipated blast loading, SHM could be used for rapid condition screening, to provide, in near real time, reliable information about the performance of a structural system during the event and about the subsequent integrity of the system itself. On the other hand, owners of buildings and civil infrastructures need information on the actual state of the structures in order to realize effective life-cycle management plans and reduce the economic and social impact of maintenance. In fact, inspections and repairs entail huge direct and social costs due to the interruption or reduction of the structure serviceability. Such information can be collected and elaborated by means of adequate monitoring systems but their diffusion is still limited by the high cost of sensors and devices needed. In this work, the realization of a monitoring system on some bridge piers of the " Himera " viaduct, located in Italian A19 Palermo-Catania highway and recently damaged by a landslide, is presented. The proposed monitoring system aims to observe the global stability of the un-collapsed side of the viaduct during the demolition works of the other side and it is intended as a quasi-real-time alert tool able to send data and warning messages to an operations center. In order to contain costs, low-cost Micro Electronic Mechanical System (MEMS) sensors have been used for the monitoring. The architecture and main features of the developed monitoring system are described in detail and the preliminary results, recorded during the first months of the campaign, are reported and discussed. Since the proposed monitoring system is still a prototype, it has been necessary to provide a metrological characterization campaign in laboratory conditions in order to define a calibration law to correct the acquired data and to estimate the sensitivity and the accuracy of the measurements. The results proved that the proposed system can be used for the monitoring of civil structures and infrastructures.
... The modal parameters thus obtained can then be used to calibrate numerical models by adjusting their mechanical properties [5]. Among the non-invasive methods the Operational Modal Analysis (OMA) is the most commonly used [4,15,42]. By measuring the response to ambient vibrations and assuming that the input is white noise, the modal properties can be defined based on the system identification process. ...
Article
Heritage buildings in Latin American countries possess high architectural value. Studying these constructions under extreme loads, particularly earthquakes, requires representative models for simulating expected response. At present, the non-invasive Operational Modal Analysis (OMA) tests offer interesting possibilities for obtaining modal parameters to update and validate a structural model for this type of structure. In this context, this article focuses on the calibration and adjustment process for a finite element model of the Metropolitan Cathedral of Santiago Chile, based on experimentally identified modal and mechanical material properties. Accordingly, an in situ experimental campaign, aimed at obtaining the response of the structure due to ambient vibrations is presented and discussed. Six high-sensitivity synchronous triaxial accelerometers were employed in this campaign. Enhanced Frequency Domain Decomposition (EFDD) and Stochastic Subspace Identification (SSI), system identification methods, were applied. Mechanical tests were performed on the Cathedral’s stone blocks. The experimental data and derived modal properties were used to generate and update a finite element model. Several considerations were made in the model updating process: the most relevant was the homogeneous treatment of the stone masonry with their mortar interface, and the boundary elements restraining effect caused by adjacent structures. A preliminary model updating process was applied to define the boundary conditions and initial material properties. This optimization was based on minimizing an error function given by the difference between the experimental and analytical frequencies. A second step was then applied, in which models with different material properties were evaluated within a physically possible range. The final model selection was based on the distance between the experimental and analytical frequencies, and the mode shapes. The updated model allows an assessment to be made of the structure behavior in its current condition and models to be prepared for a wide range of possible future research scenarios.
... Therefore, it is difficult to predicate type and location of deformations of this type of buildings that made some researchers recommend, for an effective structural health monitoring, distributing redundant sensors (De Stefano, 2007). Other researchers have proposed a numerical modal analysis using finite elements (FE) to choose the appropriate locations for monitoring sensors (Bilello et al., 2016, Elyamani et al., 2016, or employing digital photogrammetry and terrestrial laser scanning to obtain the finite element model (FEM) (Yardım and Mustafaraj, 2015). Consequently, the required technique should have the ability to detect unpredictable deformations. ...
Article
Full-text available
One of the most vital duties for engineers is to preserve life and nature by utilising safe designs that take into account environmental standards and monitoring the performance of structures against design criteria. Furthermore, monitoring can be used to determine any required maintenance of an important structure following a catastrophic event. Numerous different techniques and instruments can be employed for such a purpose with different requirements producing different results. For instance, some techniques need to embed sensors inside the building, such as Geotechnical Sensors. Others can offer high quality, but with a low point density and require fixed stations and targets, like Total Stations (TS). In such cases, the location of deformation tends to be known, such as in dams, bridges, and high-rise buildings. However, this is not always the case where it might be hard to expect deformation location as in the case of historic ruins where each part of the structure could be subject to deformation. The challenge in such case is to detect the deformation without any previous knowledge. Remote Sensing (RS) techniques, such as Digital Photogrammetry, Synthetic Aperture Radar (SAR), Interferometric Synthetic Aperture Radar (InSAR), and Terrestrial Laser Scanner (TLS) can be solutions for such an issue. Interestingly, many researchers are focusing on using TLS for monitoring owing to the great spatial resolution system can offer. However, there are three challenges in using TLS in monitoring: the first one is a huge amount of data and the difficulty of handling it; the second one is the difficulty of comparing between two epochs because observations of TLS are not repeatable; and the third issue is the noise which is attached to the data. The first problem is solved by segmentation and point structure while the second and the third ones still need more investigation, although some interesting researches have been done in this area. The aim of this research is to develop a new approach to detect and localise unpredictable deformation. It is based on TLS measurements and Generalised Procrustes Analysis (GPA) techniques to determine deformation vectors, while boxing structure and F-test are used to detect and localise deformation. In summary, after applying this approach, the whole concerned building is represented as parts, for each of which the displacement vector and the deformation probability are estimated. Ultimately, it is possible to monitor any part through different epochs. In addition, through this technique, it is possible to determine deformations - not just between two epochs, but for sequences of them. This can give more reliable results. Four validation experiments have been conducted. The first test was designed to assess the performance of the developed software and to fix some variables. Therefore, it was based on simulated data with controlled white noise, distributed according to the normal distribution, and simulated deformations. The results of this test revealed the success of the proposed algorithm to detect and to localise deformations. In addition, it showed the success when no deformations exist. Furthermore, optimistically, it could observe deformations with magnitude less than the noise level; however, the probability was only 40%. Correspondingly, real scan data with simulated deformations was used in the second test. The purpose of this test is to examine the performance of the proposed method in case of real errors budget. However, the short range of the test (about 10m), a featureless scanned area (wall only), and scanning from one position for all epochs (no need for registration) can reduce errors to a minimum. Results of this test showed the success of the proposed method to detect and localise deformations. Potentially, it can give indications for areas with deformations less than the noise level. Furthermore, results of the proposed method can be considered better than that of CloudCompare software. The third test was conducted to examine the performance of the proposed technique regarding different materials and textures. For this purpose, the Nottingham Geospatial Building (NGB) was selected with more extensive ranges (between 20-25 m). Similar to the second test, all measurements were taken from the same scanner position. To some extent, the proposed technique succeeded to detect and to localise deformations. However, the researcher does not recommend it for monitoring modern and complicated buildings, instead it has been developed for monitoring historic ruins. Finally, the proposed method was applied on the Bellmanpark Limekiln, Clitheroe, Lancashire monitoring project. This is a live project for Historic England and addresses a historic building that currently has some structural issues. The outcome of the proposed method revealed deformations in the faces South East (SE) and North East (NE). From examining these faces, three deformed areas were found: two in the face SE and one in the face NE, which might cause some cracks appeared in these faces. Alternatively, the CloudCompare software has been employed to detect deformation. Although results coincide with the proposed method for detected deformations, it cannot locate these deformations very well because it diffused over a wide area. In addition, it cannot determine actual directions of the deformations unlike the proposed method.
... Dynamic tests supply information about the whole-body response, and allow to extend to the whole structure the outcomes of the local inspections and measures. In the past, relevant examples of dynamic monitoring included, among others, towers and minarets [7][8][9][10][11][12][13][14][15][16][17][18], arched structures [19,20], churches [4,[21][22][23][24][25][26][27], or domes and other monumental structures [28][29][30][31][32]. These techniques are particularly appreciated in CH fields because of their usual non-invasiveness and non-destructiveness, and because provide indirect information about structural integrity. ...
Chapter
In the case of heritage buildings, non-invasive techniques are of paramount interest, especially those that can exploit the natural vibration of the structure. Structural Health Monitoring (SHM) can play an important role in the preservation of architectural heritage, especially when it can support a rapid and reliable assessment of structural damage and degradation. More specifically, vibration-based monitoring may help to predict the dynamic response of a structure during seismic events, as well as the damage mechanisms activated by ground motions. This information will in turn allow the selection and development of effective protection strategies. This chapter reports a discussion about the methodological multi-disciplinary approach to SHM, with emphasis on vibration-based SHM techniques, as applied to architectural heritage buildings and structures, along with the description of selected case studies. These examples were chosen in order to cover the various issues connected to design, aims and scopes of the dynamic and seismic SHM, and interpretation of the recorded data.
... Vibration-based Structural Health Monitoring (vSHM) is being increasingly used for the structural evaluation of historical buildings, such as bell towers [5][6][7][8][9], and stone masonry churches [10][11][12][13], because it allows to collect automatic real-time data which provide insights regarding structural vulnerability [14], strengthening needs [15] or the occurrence of damage [16]. The most common developed procedures to obtain automatic and accurate estimations of the modal parameters from dynamic data are based on Data-driven or Covariancedriven Stochastic Subspace Identification methods (SSI-Data o SSI-Cov) [17,18], because these methods are able to identify closely spaced modes [19]. ...
Article
The analysis of the evolution of modal properties and its relationship with changes in environmental properties (i.e. ambient temperature and relative humidity) is of high importance since their effects along time can mask the influence of structural damage. While structural monitoring studies to assess the relationship between modal parameters and environmental conditions are abundantly available for modern materials constructions (i.e. concrete or steel), very few studies are reported for adobe buildings. The present paper focuses on the study of the short and long-term structural behavior of existing adobe buildings through the long-term monitoring of ambient vibration and environmental conditions. With this purpose, the paper describes in detail the case study of the San Pedro Apostol Church of Andahuaylillas located in Cusco, inside the Andean region of Peru, a 16th-century church considered as a masterpiece of South American baroque architecture. The paper starts with a historical, architectural, and structural description of the case study. Then, it describes the implementation of a long-term monitoring system of ambient vibration and environmental variables, as well as the results of almost one year of continuous monitoring process. Finally, the obtained results of natural frequencies are correlated with ambient parameters, demonstrating different timescale influences in the modal properties due to daily and seasonal variations of the environmental conditions.
... Among the SHM approaches, one of the most popular is based on Operational Modal Analysis (OMA) techniques and the use of modal parameters as damage-sensitive features [1][2][3]. Moreover, the technological advances and the consequent easier installation of dynamic monitoring systems on both large infrastructures [1][2], [3][4][5][6] and Cultural Heritage structures [3], [6][7][8][9][10] have favored the studies on vibration-based SHM. ...
Conference Paper
Within the contest of vibration-based monitoring, the paper summarizes the conceptual development of automated procedures of modal parameter estimation (MPE) and modal tracking (MT). The performance of the proposed algorithms is demonstrated using data collected both in single data-sets and over a period of continuous monitoring. The MPE process, based on the automated interpretation of the stabilization diagram associated to any parametric identification methods, is exemplified by using the SSI-Cov technique and consists of three key steps: (1) filtering a high number of spurious poles in the stabilization diagram (2) clustering process and (3) improving the accuracy of the estimates. Eventually, the mean modal parameters are computed for each clustered mode. The MT task is based on the definition of: (a) a pre-selected list of baseline modes with adaptive thresholds and (b) a dynamic reference list of modes associated to fixed thresholds.
... Concerning the masonry churches, Ramos et al. [4] and Masciotta et al. [9,10] monitored the Church of Monastery of Jeronimos. Elyamani et al. [11] monitored the Mallorca cathedral (Mallorca Island, Spain) under ambient sources of vibration and seismic events. A few months ago, Gentile et al. [12] reported on the long-term monitoring of the Milan cathedral, which hosts the most extensive monitoring system ever installed in a cultural heritage monument. ...
Article
The Santa Maria di Collemaggio basilica is a 13th-century masonry masterpiece. The restoration works following the 2009 earthquake in L'Aquila included the installation of a permanent monitoring system. Crack gauges monitor a few significant cracks that appeared during the 2009 earthquake. Force-Balance accelerometers record the dynamic response of the entire structure. The dynamic response to ambient excitation leads to the estimation of the modal parameters. The current paper reports the outcomes of two years of static and dynamic monitoring from 1/1/2018 to 31/12/2019. The authors correlated the outdoor temperature and relative humidity to both the amplitude of the cracks and the modal parameters. The temperature deeply affects the static and dynamic response of the basilica. However, the linear correlations between the temperature and the structural response are diverse. There are cracks which stretch when the temperature rises and cracks which act oppositely. Natural frequencies lower when the temperature rises, while the same modes exhibit modal interaction phenomena. Furthermore, the natural frequencies of the basilica are not stationary but are moderately declining across the years. The basilica is a complex structure, where the different constitutive behaviour of three different materials, masonry, steel and timber may yield a varied structural response. The authors attempt to provide a qualitative interpretation of the observed behaviour, namely the detected correlations to the outdoor temperature, the lowering of the natural frequencies across the years and mode interaction phenomena.
... About the masonry churches, L.F. Ramos et al. (Ramos et al. 2010), and Masciotta et al. (Masciotta, Ramos, and Lourenço 2017;Masciotta et al. 2016) monitored the Church of Monastery of Jeronimos. Elyamani et al. (Elyamani et al. 2017) monitored the Mallorca cathedral (Mallorca Island, Spain) under ambient sources of vibration and seismic events. Gentile et al. (Gentile, Ruccolo, and Canali 2019) reported on the long-term monitoring of the Milan cathedral, which hosts an extensive monitoring system. ...
Article
The long term dynamic monitoring of the Santa Maria di Collemaggio basilica revealed an unexpected trend of the first natural frequencies decreasing from their initial values estimated in 2018. The decrement of the natural frequency could originate from several factors. The structural system derives from the arrangement of four building materials: masonry (predominant), reinforced concrete (RC), timber and steel. Masonry is unlikely to suffer rapid decaying of its mechanical properties. Reinforced concrete (RC) and embedded steel should not present decaying phenomena in the first years after built. Likewise, the steel plates which connect the Cross-Laminated Timber (CLT) panels should not manifest a significant progression of corrosion in an indoor environment. Conversely, timber's physical and mechanical properties, such as swelling and shrinkage, density, modulus of elasticity, strength have a time-dependent response, even in the long term. Likely, the decaying of the natural frequencies depends on the CLT roof's time-dependent behaviour due to the potential modification of its mechanical properties and boundary conditions (interaction with the steel plates, e.g.). This paper presents selected results from the basilica's three-year continuous dynamic monitoring and discusses an elementary mechanical model representative of the dynamics transverse to the nave walls. The mechanical model described by a limited set of parameters drives the assessment of the CLT roof's possible role in causing the detected decrement of the natural frequencies.
... Modern tools were developed to assess existing buildings and reduce their vulnerability. Within the available tools, vibrationbased structural health monitoring (vSHM) is finding an increasing use in the preservation and conservation of historical constructions such as bell towers [5], stone masonry churches [6] and buildings [7] due to its low invasiveness, the possibility to increase of the level of knowledge of structural system with high accuracy and the possibility of check the health state of the structures [8]. The structural health assessment of existing buildings by vibration-based monitoring systems is a challenge task because the influence of the environmental parameters (mainly temperature and humidity) can lead a variation of the boundary conditions [9], in the system stiffness [10] and others, masking variations due to structural damages. ...
... They found that the lighthouses have fundamental natural frequencies in the horizontal direction in the range of 4 − 6 and they are stiff enough. Elyamani et al. [70] investigated the dynamic properties of a large historical cathedral in Spain using ambient vibration tests. Ambient vibrations mainly come from wind from seaside and people or traffic movements. ...
Thesis
Historic Cairo is a UNESCO World Heritage Site since 1979. It has more than 600 of historic structures which require many studies and research to keep their cultural, religious, and economic values. To contribute to this research scheme, the current thesis provides an updated numerical model for the dome of Fatima Khatun, a historic mausoleum in Historic Cairo dating back to the 13th c. consisted mainly of bricks and stones. A preliminary numerical finite element model was created based on a recent conservation study which includes detailed architectural documentation of the structure and material survey. Physical and mechanical properties of different materials employed into the model have been estimated based on literature review and laboratory testing of samples taken out of the structure. The boundary conditions of the numerical model have been defined based on the available soil profile and visual inspection. The modal analysis of the numerical model has identified the dynamic properties of the structure under the estimated material properties and boundary conditions. System identification has been carried out using in-situ dynamic investigation tests to calibrate the preliminary model to the actual state of the structure during the time of testing. This process managed to capture three experimental natural frequencies of the structure with their shapes and damping ratios. To easily update the model, a Neural Network was created as a new numerical representation of the structure. A database of 8000 different models have been created using this neural network. By searching this database for the experimental frequencies, it was easy to determine the numerical model with the natural frequencies that match the experimental ones. The obtained updated model could be employed in further studies for the structural safety assessment.
... A historical timber and masonry building in Izmir, Turkey from 19th century was investigated with AVTs to evaluate the retrofitting of the building followed by FE dynamic analysis with recorded earthquakes [10]. The dynamic behavior of Mallorca cathedral at Mallorca Island, Spain was monitored under ambient vibration as well as earthquake events of small seismic events of Mallorca Island [11]. The Metropolitan Cathedral of Santiago, Chile that its construction spanned more than 150 years (1748 to 1906) and during this period had experienced two earthquakes of 1851 and 1874, was investigated by ambient vibration tests and FE analysis for identification of the fundamental frequencies and calibration of mechanical properties of the numerical model of the building [12]. ...
Article
Full-text available
Eight historical mosques of Kermanshah constructed in 18th or 19th century CE are investigated with ambient vibration tests on their sites and buildings. Conventional peak picking technique is used for determination of structures’ fundamental frequencies and spectral ratio of horizontal to vertical components along with ellipticity inversion of Rayleigh waves are considered to identify the natural frequency of ground and shear wave velocity profile to define the site conditions according to the national codes of Iran and Italy. The recorded motions on the buildings are used to calculate the fundamental frequencies of the structure. Afterward, buildings are modeled by macro-element method and material properties are tuned in the way that the fundamental frequencies from the modal analyses match with the measured values from AVTs. Finally, more modal analyses are performed by the calibrated models to present an empirical relation between the natural period of the mosques, the geometrical characteristics of the buildings, and the mechanical properties of the construction materials. The results show that the natural periods of the masonry buildings of the mosques are different from the values of empirical relations in the national codes. Meanwhile, the proposed empirical relation presents the natural periods of the buildings of this study reasonably well and can be used for other masonry buildings of similar architecture and materials.
... It is known that environmental actions, especially temperature, have an influence on the behaviour of masonry heritage buildings, such as towers (Cabboi et al. 2017;Azzara et al. 2018;Tronci et al. 2020), cathedrals (Elyamani et al. 2017;Gentile et al. 2019) and palaces (Kita et al. 2019). Roje-Bonacci et al. (2014) demonstrated that, in the case of Saint Lawrence Cathedral, there is a strong correlation between crack openings and air temperature. ...
Article
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Continuous monitoring was carried out on the Ile Vierge lighthouse, the tallest stone lighthouse in Europe (82 m), built in 1902, where the upper part of the tower presents a crack pattern. The monitoring was implemented over 2.5 years to characterize the actions of temperature and wind and to determine their links with crack opening. The variation of each factor measured was analysed and possible correlations between the variables were sought. In addition, the temperatures measured on site were compared with the actions required by Eurocode 1. The quantity of data extracted made it necessary to develop a data analysis method combining Principal Component Analysis, Multiple Regression Analysis, and Artificial Neural Network Analysis. Thus, the long- and short-term behaviour of the instrumented cracks could be identified. The relative influences of the wind and the temperature on crack opening were given by a percentage assessment.
... The outcomes of continuous dynamic monitoring reveal the time evolution of modal parameters and the related environmental effects on the dynamic response. Accurately, several scholars estimated both positive and negative correlations between the natural frequency and the measured temperature Azzara et al. 2018;Elyamani et al. 2017;Gentile, Ruccolo, and Canali 2019;Kita, Cavalagli, and Ubertini 2019). On the contrary, dynamic identification takes a sort of photographic shot of the dynamic response in a limited time interval in terms of modal parameters. ...
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The paper delivers a short report about the modal identification carried out on a historical masonry palace in the city centre of L'Aquila, Palazzo Pica Alfieri, retrofitted after the 2009 earthquake. A concise description of the damage pattern and the retrofitting interventions heads the presentation of the results of the dynamic identification using Operational Modal Analysis. The identified mode shapes and natural frequencies drive a discussion about the detectability and the assessment of the modifications induced by the structural interventions using low-vibration measurements. Differently from more uncomplicated structures, the production of a Finite Element model representative of an existing masonry complex requires considerable efforts: the masonry structure may not behave like a continuum, due to the presence of cracks and unknown structural discontinuities. Still, the results of the dynamic identification bestow valuable information about the structural behaviour from a qualitative viewpoint, even if not backed by a faithful FE model. The paper addresses the aspects possibly related to the dynamic identification of a monumental masonry building, based on the shreds of evidence arisen from the presented case study.
... Despite the minimum impact of vibration-based SHM, that makes this methodology especially suitable to the context of Cultural Heritage (CH) preservation, the practical applications in this field are still not frequent [3][4][5][6][7][8][9][10] and generally based on the use of a limited number of sensors. The installation of a few sensors to assist the preservation and perform the SHM of CH structures has recently revealed very promising for ancient towers [4,9]. ...
Conference Paper
Continuous monitoring of the structural response under ambient excitation is especially suitable to Cultural Heritage structures because of the fully non-destructive and sustainable way of testing, that is performed by just measuring the dynamic response under ambient excitation and does not involve additional loads rather than those associated to normal operational conditions. Within the context of vibration-based monitoring of historic masonry structures, the paper presents the development of an automated procedure of modal parameters estimation and tracking, as well as its application in the continuous dynamic monitoring of a masonry bell-tower. The proposed algorithm of modal parameters estimation is based on the interpretation of the stabilization diagram associated to parametric identification methods and consists of three key steps aimed at: (1) filtering a high number of spurious poles in the stabilization diagram; (2) clustering the stabilization diagram; (3) improving the accuracy of the estimates. The developed procedure is exemplified using the data collected on the bell-tower of the church of San Gottardo in Corte in Milan. Following the practice adopted by the authors for masonry towers, a simple dynamic monitoring system is installed in the tower: the monitoring system includes two bi-axial seismometers (electro-dynamic velocity transducers), one 24-bit digitizer (6 channels, A/D converter, 8 Gb Ram on board for data storage) and one UMTS modem for data transfer. After a concise presentation of the developed automated algorithm, the paper focuses on the results obtained in several months of continuous monitoring of the tower.
... Structural Health Monitoring (SHM) approaches have been in constant evolution for decades thanks to advances in sensing technology and computational capabilities [1][2][3]. Recent structural collapses around the world stressed out the necessity of having monitoring systems able to identify the health state of structures, particularly the ones that have strategic importance or historic value [4], located in highly seismic areas [5][6][7]. Therefore an efficient monitoring system, combined with an optimized vibration-based identification approach, allows engineers tracking the dynamic response of the structure, offering the possibility to check its integrity level continuously over time. The vulnerability of structures has been taken into account also in terms of innovative design or renovation strategies and several vibration control techniques have been introduced in new as well as old buildings, like active, passive and semi-active vibration control systems (e.g., Viscous Dampers, Tuned Mass Dampers, Tuned Liquid Column Dampers, Tuned Liquid Dampers, etc.). ...
Article
This article presents the development and the results of three years of implementation of an automated vibration-based structural health monitoring system for modal tracking the dynamic characteristics of a concrete masonry Civic Tower in Rieti (Italy) equipped with a passive vibration control system, a Non-Conventional Tuned Mass Damper. The system is based on the data recorded by a small number of high-sensitivity accelerometers set on remote automated modal parameters tracking. The analysis of monitoring data highlights the main characteristics of the response of the tower to operational vibrations and low-return period earthquakes. Despite the low levels of vibration in operational conditions, the system can track the evolution of the structural frequencies along time and successfully capture their dependence from temperature, both daily and seasonally. Moreover, the robustness of the modal identification procedure allowed the detection of anomalous variation from the validated reference dynamics of the structure.
... The first step of the calibration (Elyamani et al. 2017) consisted in removing the conical cover of the tower. During the AVT, that part of the tower was not instrumented due to access difficulties, thus it was considered a dead load in order to eliminate its influence on the first modes. ...
Article
Central Italy Earthquakes occurred in 2016 pointed out once more the vulnerability of Cultural Heritage (CH), especially for what concerns bell-towers since they tend to get dramatically damaged due to their considerable slenderness and deterioration, endangering their surroundings and making their preservation fundamental. This work presents the results of the study carried out on four different isolated masonry bell towers, located in Ferrara province (Italy); the parameters of the materials were deduced by calibrating Finite Element Models (FEMs) using the data collected during an investigation campaign conducted with a wired accelerometric sensor system, since it was not possible to apply destructive methodologies. Dynamic data were extracted through the application of two Operational Modal Analysis (OMA) identification techniques: the Enhanced Frequency Domain Decomposition (EFDD) and the Stochastic Subspace Identification (SSI) methodology. Particular attention was devoted to the use of MAC matrix in the validation of the mode shapes results.
... In the case of historic buildings both sources of data are often restricted either because of the lack and incompleteness of documents in archives or because of the impossibility to perform invasive tests that may compromise the integrity of the constructions (Bartoli et al., 2012). In this context, structural health monitoring (SHM) techniques appear to be particularly attractive De Stefano et al., 2016;Gattulli et al., 2016;Lorenzoni et al., 2016;Elyamani et al., 2017;Clementi et al., 2017;Masciotta et al., 2017a). They are based on the continuous observation -by means of sensors -of a physical phenomenon which is related to the health of the structure (Peeters et al., 2001;Worden et al., 2002;Magalhães et al., 2012). ...
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This paper addresses the structural health monitoring (SHM) of the bell tower of the Basilica of San Pietro in Perugia, Italy, which is located in a seismic area. Known as one of the landmarks of the Umbrian capital, the tower belongs to a monumental complex of exceptional historical and cultural value. Therefore, its protection with respect to earthquakes is an important issue. To this purpose, a vibration-based SHM system able to detect anomalies in the structural behaviour by means of statistical process control tools has been installed in the tower and is under continuous operation since December 2014. The effects of the 2016–2017 Central Italy seismic sequence were clearly detected by this system, even if earthquakes took place at relatively large distance from the bell tower. The large amount of SHM data collected over four years allowed to assess the modifications in the structural behaviour of the bell tower in post-earthquake conditions.
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Recent ground-breaking advances in sensing technologies, data processing, and structural identification have made Structural Health Monitoring (SHM) occupy a central place in Structural Engineering. Although the technological transfer to the industry is still in the early development stages, there is clear evidence that SHM-enabled condition-based maintenance of structures will soon supersede traditional periodic maintenance strategies. Among the existing solutions, ambient vibration-based SHM has become particularly popular owing to its minimum intrusiveness and global damage assessment capabilities. Nevertheless, it is well documented that local pathologies with limited impact over the stiffness of structures can be hardly detected by such techniques. As a solution, recent studies advocate the use of integrated monitoring systems, where data from heterogeneous sensor networks are simultaneously processed to achieve a comprehensive structural assessment. Despite the great advances of these systems reported by researchers, practitioners still find many difficulties to bring them to practice. In this light, this paper reports the development of two novel software solutions for long-term SHM of structures, MOVA and MOSS, that are intended to bridge this gap while also introducing new methodological and scientific advances. The developed software enables the online system identification and damage detection of structures, including vibration-based SHM and data fusion of heterogeneous sensing systems with an innovative automated anomaly detection algorithm. A case study of a permanent static/dynamic/environmental monitoring system installed in a monumental masonry palace, the Consoli Palace in Gubbio (Italy), is presented to illustrate the capabilities of MOVA/MOSS.
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Combined non‐destructive techniques are applied in the study of a historical building in Barcelona. Santa Maria del Mar is a magnificent Mediterranean gothic church built between 1329 and 1383. Two of the most important characteristics of this building are the slender columns and the almost flat rooftop. This structure, used to create a visual impression of a unique space, transmits high loads to the tall columns. Previous to restoration, vaults, roofs, and columns were extensively assessed with non‐destructive tests, in order to improve the knowledge of those structures. This information will be used in further simulations to analyse load distributions at each part of the structure. Ground and floor were also studied. The analysis of the columns was based on ground‐penetrating radar (GPR) surveys and on seismic tomography. Finally, the dynamic behaviour of the structure was determined by seismic monitoring of the main nave and the bell tower. Results obtained at the radar survey highlight the existence of unexpected anomalies in homogeneous materials, supporting the hypothesis of an inner structure between arches and roof composed by hollow elements. Seismic tomography defined the inner geometry of the columns and detected some damage or lower quality stone in various zones. Seismic monitoring established the perfect junction between the bell tower and the main nave. GPR survey on the floor allowed detecting a large number of graves, and some images suggest the existence of large underground walls and some of the foundations of the main façade.
Article
Detection of structural damage is an important issue. Some techniques require knowledge of the undamaged state or in-depth knowledge of the construction materials used. The application of principal component analysis to the temporal variation in natural frequencies is a promising technique. With an undamaged structure a single principal component will suffice to explain the change in modal frequencies with weather variables, whereas more components are needed in the case of damaged structures. Like all other detection techniques, it has advantages and drawbacks. The main advantages are the ability to work without knowledge of the previous state of the structure, the relatively short monitoring time required (about 10 days), low cost, and low number of instrumentations. The main drawback is the need for more studies to correlate degree of damage with the number of principal components. This paper presents the results obtained for six structures: Mallorca Cathedral, four university buildings in Barcelona, and a reduced model structure in a laboratory. We also propose a semiautomatic algorithm to track modal frequencies over time and add a discussion of operational modal analysis in real buildings.
Chapter
This work reports the development of two novel software solutions, named MOVA and MOSS, for the autonomous management of integrated monitoring systems. MOVA and MOSS, Italian acronyms of “MOnitoraggio delle Vibrazioni Ambientali’’ and “MOnitoraggio dello Stato di Salute’’, respectively, offer online operational modal analysis (OMA), pattern recognition, feature extraction through data fusion, and automated novelty detection capabilities. The functionalities of the developed codes are illustrated through the application case study of the monumental Consoli Palace in Gubbio, Italy. The palace was uninterruptedly monitored since July 2017 until August 2019 with a mixed static/dynamic/environmental monitoring system, and the SHM system has been recently upgraded in July 2020 with a considerable increase of the number of sensors deployed in the palace.
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This paper presents a vibration-based model updating procedure for historical masonry structures which have suffered severe damage due to seismic events. This allows gathering in-depth insights on the current condition of damaged buildings, which can be beneficial for the knowledge of their actual structural behaviour and, consequently, for the design of repairing and strengthening interventions. The methodology, based on the experimentally identified modal parameters, is tested on the San Felice sul Panaro medieval fortress, which was heavily damaged by the 2012 Emilia earthquake. The finite element mesh of the structure in its post-quake condition is generated by means of a nonstandard semi-automatic mesh generation procedure based on a laser scanner points cloud. Ambient vibration testing is performed on the main tower of the fortress. Mechanical properties of the tower and the level of connections with the rest of the fortress in its current damaged state are investigated. To fully characterize the actual behaviour of the tower in operational condition, mesh elements corresponding to the damaged masonry are identified and different material properties are assigned to them. This allows to account for the effect of damage and cracks, which appeared essential in the calibration process. The updating procedure is carried out by means of an advanced surrogate-assisted evolutionary algorithm designed for reducing the computational effort.
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The cemetery of the royal family, who ruled Egypt from 1805 to 1952, is one of the masterpieces of the UNESCO World Heritage Site of Historic Cairo. It is a complex building from massive stone masonry walls supporting hemispherical domes and is very rich with the marble decorative elements. Unfortunately, it suffers nowadays from serious cracking due to on-going structural damage. Almost all the structural elements are cracked. Besides, the continuous rise in the groundwater table affects both its structural stability and aesthetics. A detailed inspection was carried out to identify and explain all the manifested damage by the structural elements of the cemetery. The differential settlement damage was found to be very noticeable in the form of many diagonal cracks that are active and threaten the overall stability of the cemetery. The construction history was investigated and found to have a clear effect on the noticed damage. Examination of the construction materials and deterioration products was carried out by inspecting representative samples of the stone, the marble, the mortar, the plaster and the salt. They were examined using different analysis techniques including the Polarized Microscope, the Stereo Microscope, the X-Ray Diffraction (XRD), and the Scanning Electron Microscope (SEM) provided with Energy-Dispersive X-ray spectroscopy (EDX) unit. This examination helped in identifying the type of the used stone, the mortar components, the types of salts affecting the structure, and the deterioration manifested by the marble. It seems that the cemetery needs an urgent conservation project to stop the deterioration and keep it safe for the next generations.
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This paper proposes simplified formulations for estimating the main frequencies of ancient masonry churches. The formulations are derived starting from the results of numerical analyses with finite elements models, whose geometric parameters are assigned in accordance with specific relationships established on a set of 50 existing churches. The so-obtained formulations are also compared with the results of a series of experimental dynamic identification tests chosen from literature. Finally, starting from these experimental results, through numerical regressions, formulas for predicting the main frequencies of ancient masonry churches are proposed, too.
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Islamic monumental buildings in Egypt, generally, and in Cairo, specifically, suffer from a number of typical problems such as: lack of maintenance, raising of ground water levels, and spread cracks in structural elements. As well, the surroundings of such buildings suffer from a number of typical problems such as: harmful anthropogenic actions including heavy traffic, pollution resulting from industrial activities, and constructing new buildings beside these buildings. The new buildings affect negatively on the monumental buildings’ visual impact. This research aims at throwing the light on such typical problems in one of the unique mosques in Cairo which is Queen Safiyya mosque. It is an Ottoman mosque built at the beginning of the 17thc (11thc AH). The mosque suffers now from a number of theaforementioned problems. The spread cracks and the big settlement in the mosque floor could be considered one of these major problems. As well, the mosque’s surroundings suffer from pollution and harmful anthropogenic actions. The paper discusses the building history and description and the signs and factors of the observed damage specified based on visual inspection. A number of intervention proposals are given. A number of studies were carried out on the surroundings including the demographics, the buildings and the lands. A number of rehabilitation measures were proposed based on these studies. This paper is a start for more research that should be conducted on the mosque and its surroundings and similar monumental buildings in Egypt. The target is to protect these buildings from continuous deterioration which may result at end to the total loss of such buildings and deprivation next generations from valueless part of the Egyptian architectural heritage.
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In recent years, Structural Health Monitoring (SHM) based on Operational Modal Analysis (OMA) and damage detection tools has become a popular non-destructive solution to assess the real-time integrity of any kind of structure. This technique is especially well-suited for the condition-based conservation of historical structures, where minimal invasiveness must be ensured owing to their high cultural and architectural value. Optimal Sensor Placement (OSP) techniques represent a valuable tool for efficiently designing the sensor layout in a SHM system in order to achieve an effective modal identification with a reduced number of sensors and, consequently, an improved cost efficiency. In this light, this paper proposes a design methodology of sensor networks based on OSP techniques suitable for historical structures. To do so, a preliminary extensive OMA campaign is conducted in order to construct a reliable finite element (FE) model by fitting the identified modal properties. Afterwards, an optimal sensor arrangement with a limited number of sensors is obtained by applying different model-based OSP techniques. In order to improve the robustness of the solution, material uncertainties are included in the model and the optimal sensor placement is conducted within a statistical framework. This methodology is presented and evaluated with a case study of a Spanish secular building: the Monastery of San Jerónimo de Buenavista in Seville (Spain). In particular, this paper presents the results of the preliminary ambient vibration test and the modal identification of the monastery, the updating process of the FE model, as well as a critical review of the different OSP techniques within a framework of material parameter uncertainty. The presented analysis demonstrate that OSP techniques based on the rank optimization of the kinetic energy matrix of the structure yield robust sensor layout.
Chapter
The long term dynamic monitoring of the Santa Maria di Collemaggio basilica revealed an unexpected trend of the first natural frequencies decreasing from their initial values estimated in 2018. The decrement of the natural frequency could originate from several factors. The structural system derives from the arrangement of four building materials: masonry (predominant), reinforced concrete (RC), timber and steel. Masonry is unlikely to suffer rapid decaying of their mechanical properties. Reinforced concrete (RC) and the embedded steel should not present decaying phenomena in the first years after built. Likewise, the steel plates which connect the Cross-Laminated Timber (CLT) panels should not manifest a significant progression of corrosion in an indoor environment. Conversely, timber’s physical and mechanical properties, such as swelling and shrinkage, density, modulus of elasticity, strength have a time-dependent response, even in the long-term. Likely, the decaying of the natural frequencies depends on the CLT roof’s time-dependent behaviour due to the potential modification of its mechanical properties and boundary conditions (interaction with the steel plates, e.g.). This paper presents selected results from the basilica’s three-years continuous dynamic monitoring and discusses an elementary mechanical model representative of the dynamics transverse to the nave walls. The mechanical model described by a limited set of parameters drives the assessment of the CLT roof’s possible role in causing the detected decrement of the natural frequencies.
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Historical structures are vital to the realization of how the technical, artistic, and scientific skills of the human kind have developed over time. These structures are one of the motors of the tourism industry, and therefore, the studies related to their conservation do not only have social benefits but as well economical ones. It is unfortunately that many countries rich with valuable architectural heritage are characterized by high seismic activity, Italy and Turkey are obvious examples. Due to earthquakes, many invaluable historical structures have been lost forever. Consequently, there is an increasing need for more research on the topic of seismic assessment and protection of this class of buildings. This work contributes to the methodological approaches adopted for the seismic assessment of historical structures. In many cases, due to the lack of knowledge about the assessed historical structure, it is essential to combine many investigation activities in such approaches. The aim is to minimize any possibly required seismic strengthening interventions (minimum intervention concept) by increasing the level of knowledge about the structure. In the current research, the employed experimental investigation activities are the dynamic identification tests and the dynamic monitoring. Most approaches for dynamic monitoring are based on the use of a threshold limit which is used to trigger the system when the parameters measured surpass the limit. Here, an alternative is considered that consists of a continuous monitoring system based on the permanent measurement of the ambient vibration. A thermography monitoring is used as a complementary system for the measurement of temperature. The integration between the dynamic investigation and the numerical modeling is essential and it includes two main features. On one hand, tentative structural analyses are carried out to identify important aspects of the dynamic tests and monitoring strategies such as critical points of the structure where to place the sensors. On the other hand, the results of the dynamic investigation are used to perform model updating until obtaining a satisfactory structural model adequately matching the measured dynamic properties of the structure. Once the structural model is validated, it is used to carry out the seismic assessment of the structure. This assessment is performed using different methods, to cross check the results, including the pushover analysis, the kinematic limit analysis and the nonlinear dynamic analysis. It is then possible with these assessments to identify the seismic behavior of the structure. Using the N2 method, the evaluation of the structural performance and its safety are carried out. Hence, the needs for any possible seismic strengthening are revealed, keeping in mind, the respect to the "minimum intervention" concept. As an application, the cathedral of Mallorca (Spain) is taken as a case study. This structure is one of the largest cathedrals built during the Middle Age. For each of the previously mentioned research steps, the followed criteria and the experience gained are transferred into recommended methodological approaches to be applied to other historical structures. Finally, the integration of these partial steps into one integrated methodology is discussed.
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The protection of monuments from aging and natural hazards, such as earthquakes, is very important since such structures are part of the cultural heritage of many countries around the world. In order to protect them from earthquakes, their structural system has to be identified and their capacity to withstand dynamic loads has to be clearly understood. Due to the large size of such structures and the limitations imposed by antiquities departments on the methods that can be used to obtain the properties of the materials of these structures and their dynamic characteristics, the ambient vibration survey method seems to be the most appropriate one to be used. Once the dynamic characteristics are identified, they will form a bench mark and any deviation in these parameters will be used for the identification and localization of damage caused to the structure, either due to environmental factors and aging, or due to an earthquake. In this work the dynamic characteristics of St. Nicholas Cathedral obtained through ambient vibration survey and the subsequent calibrated FE model are presented. Then a numerical sensitivity analysis is performed, in which damage in inflicted at vulnerable sections of the structure and the effects of this damage on the dynamic characteristics of the structure are recorded. Finally, conclusions are drawn on the type of sensors and locations they should be placed, as well as on the effectiveness of a monitoring system in identifying and localizing damage on the structure.
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In this paper, the experimental modal identification analysis of the public building "San Giacomo" in Corfu (Greece) is illustrated. It represents the unique example of a structure built utilising carves stones inside the city of Corfu. The building has a rectangular plan shape with dimensions 24.75 × 14 m, and height 9 m; all the floors are made by wood. The monitoring system consists of several elements properly connected: the units of acquisitions or piezoelectric accelerometers (in total 18 installed on the different walls) with a sensitivity of 1000 mV/g; the data acquisition system or DAQs positioned at each monitored level; the laptop with an acquisition software; the cables that connect all elements to each other. The paper describes the phases of the investigations, the technical details of the performed in-situ tests, the first identified frequencies of the building by means of the classical methods of Operational Modal Analysis (OMA) and the comments about the acquired data.
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The historic bell tower of the San Vittore church in Arcisate (Varese) has been studied by Politecnico di Milano since 2007. After a brief description of past operational modal tests and FE modelling, the paper focuses on the results provided by a simple dynamic monitoring system installed inside the tower for several months. The modal identification was performed using the data-driven Stochastic Subspace Identification technique and the estimated natural frequencies turned out to exhibit clear dependence on temperature. Subsequently, the modal frequencies were used to identify some uncertain structural parameters of the FE model, using the simple method proposed by Douglas and Reid (1982). Originally-identified and temperature-removed modal frequencies were used as experimental references in the identification of structural parameters and the two sets of optimal parameters (with and without the temperature effect) are presented and discussed.
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This paper presents the analysis of the structure of Mallorca Cathedral taking into account the influence on structural behaviour of auxiliary iron ties used during the construction process. Recent studies (Roca et al., 2012, 2013) have presented some hypotheses about the construction process of the cathedral. The present study complements the previous results by considering the use of auxiliary ties as temporary stabilizing device during the construction. Evidence of the use of ties during the construction has been recognized after a comprehensive survey. The study of the role of such ties and the effect of their later removal are studied by a FE analysis carried out on a representative bay of the structure. The study includes a time-dependent FE analysis after the removal of the ties to assess the long-term structural behaviour. The results of the numerical analysis are compared with the deformation trends identified by means of a recent monitoring campaign.
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This paper presents a continuum model for the simulation of the viscous effects and the long-term damage accumulation in masonry structures. The rheological model is based on a generalized Maxwell chain representation with a constitutive law utilizing a limited number of internal variables. Thanks to its computational efficiency, this approach is suitable for the analysis of large and complex structures. In the paper, the viscous and damage models are presented and their coupling is discussed. The FE simulation of the construction process of the representative bay of Mallorca Cathedral is presented, together with the analysis of the long-term effects. The parameters of the model are tentatively calibrated on the basis of the time-dependent viscous deformations detected during the cathedral monitoring.
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Recently the superior performance of the PolyMAX modal parameter estimation method using frequency response functions was demonstrated. The method can be implemented in a very similar way as the industry standard polyreference (time-domain) least-squares complex exponential method: in a first step a stabilisation diagram is constructed containing frequency, damping and participation information. Next, the mode shapes are found in a second least-squares step, based on the user selection of stable poles. One of the specific advantages of the technique lies in the very stable identification of the system poles and participation factors as a function of the specified system order, leading to easy-to-interpret stabilisation diagrams. This implies a potential for automating the method and to apply it to "difficult" estimation cases such as high-order and/or highly damped systems with large modal overlap. Furthermore, PolyMAX is computationally extremely efficient. In this paper the method will be extended to the operational case: only the structural response to some unknown inputs is available for system identification. Attention will be given to the pre-processing of the raw operational time data and the post-processing of the poles and operational reference factors to obtain the mode shapes. The paper also gives an overview of existing Operational Modal Analysis methods and discusses the positioning of PolyMAX herein.
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Ancient structures, especially very old ones, prove their soundness and the correctness of their structural layout by reaching our days in good conditions. This is the case of the Roman Arena in Verona—Italy, built in the first century A.D., and still standing in the historical centre of Verona. It became certainly the symbol of the city and it is open to public use for visits and also for operas, concerts and relevant shows. However, with a closer look, it is possible to appraise damages that the passing of time and the natural or man-induced events such as historical earthquakes and floods or wars and sieges left on the structure. Seismic events (the worst ones recorded in 1116, 1117 and in 1183) induced serious damages on the Arena since they caused the almost complete collapse of the third external ring of the monument, today only remaining in the so-called “wing” of the Arena, a freestanding curved wall composed by huge blocks of stone and characterized by a repetition of arches and massive pillars. With the purpose of evaluating the structural response of the Arena to static, dynamic (e.g. shows, concerts) and seismic loads, a structural health monitoring (SHM) system was installed in 2011, with a state-of-the-art technology to record meaningful data through a sensors’ network installed in relevant positions of the monument. A detailed crack pattern survey was carried out to identify main cracks and damages and select the most suitable positions for static sensors, able to control the reversibility of the seasonal displacements or deformations trends of the monument. Ambient vibration tests were also carried out to extract the fundamental modal parameters and calibrate/update reference finite elements models: global modes were identified and—with a special focus on the wing—acceleration sensors were installed in the areas where significant dynamic amplifications are expected according to the numerical simulation. The paper reports the preliminary activities carried out before the installation of the SHM system and illustrates the results of the first 1.5 year of monitoring analysing both the operational conditions of the structure and its response in case of exceptional events. Specific algorithms were developed and implemented to perform the continuous real-time treatment of static data and the automated identification of modal parameters.
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The paper presents the dynamic structural health monitoring activities on Saint Torcato Church, in Guimarães, Portugal, which has significant structural problems due to soil settlements. Cracks can be observed on the main and the lateral façades, the bell-towers are leaning, and the arches in the nave exhibit a failure mechanism with cracks and vertical deformations. These phenomena are progressing and a structural intervention is planned. A monitoring system has been installed to control the current condition and to assess the success of the future intervention. The paper shows the monitoring results with an emphasis in the dynamic analysis carried out before the structural strengthening, namely with respect to: experimental tests with output-only techniques for frequencies, damping and mode shapes estimation, FE model updating analysis and dynamic monitoring. The automatic system identification process uses ambient vibration signatures in combination with cluster analysis and rule-based approach for the interpretation of the results of the Stochastic Subspace Identification method
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This paper presents a continuum model for the simulation of the viscous effects and the long-term damage ac-cumulation in masonry structures. The rheological model is based on a generalized Maxwell chain representation with a constitutive law utilizing a limited number of internal variables. Thanks to its computational efficiency, this approach is suitable for the analysis of large and complex structures. In the paper, the viscous and damage models are presented and their coupling is discussed. The FE simulation of the construction process of the representative bay of Mallorca Cathedral is presented, together with the analysis of the long-term effects. The parameters of the model are tentatively calibrated on the basis of the time-dependent viscous deformations detected during the cathedral monitoring.
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The current study investigates the dynamic characteristics of two historical monuments in Cyprus, the St. Nicholas Cathedral in Famagusta and the St. Mamas Church in Morphou. The testing was performed using the ambient vibration survey approach and the output-only method for both structures, to obtain the frequencies and mode shapes of the lower modes. These results contributed in the updating of the finite element models and in the planning of the monitoring strategy that was implemented for these structures, as well as the study for their seismic vulnerability. Comparisons are made between the measured and finite element model dynamic characteristics, and conclusions are drawn.
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From the theoretical point of view, systems composed by masonry arches or vaults would require, during construction, the simultaneous activation of all structural elements in order to reach the optimum balance of thrusts. This is not obviously the case of complex ancient masonry constructions, whose long and gradual building process may have contributed to their deformed condition and even to damage.In this paper, the possible influence of the construction process as well as that of later long-term deformation on the final condition of the building is investigated in the case of a complex and large historical structure, namely Mallorca Cathedral. A FE code has been specifically developed for the present study. The code is able to account for construction processes through sequential-evolutionary analyses, with the description of masonry mechanical damage and long-term deformation. The representative bay of the cathedral is analyzed taking into account different construction phases, as emerged from historical research. The response of such substructure to transverse earthquake equivalent forces is then investigated. In this case, the damage model is improved with a local crack-tracking algorithm. This numerical strategy models the tensile damage as distinct cracks, leading to a better prediction of realistic collapsing mechanisms.
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In this paper a new frequency domain technique is introduced for the modal identification of output-only systems, i.e. in the case where the modal parameters must be estimated without knowing the input exciting the system. By its user friendliness the technique is closely related to the classical approach where the modal parameters are estimated by simple peak picking. However, by introducing a decomposition of the spectral density function matrix, the response spectra can be separated into a set of single degree of freedom systems, each corresponding to an individual mode. By using this decomposition technique close modes can be identified with high accuracy even in the case of strong noise contamination of the signals. Also, the technique clearly indicates harmonic components in the response signals.
Chapter
The paper describes the experimental procedures applied to assess the structural condition and the seismic vulnerability of the Gabbia tower in Mantua, after the seismic sequence of Spring 2012. An extensive research program was planned and carried out to support the future preservation actions, including direct survey and historic and documentary research, several experimental and numerical tasks. The paper summarizes the results provided by a wide multi-disciplinary investigation and especially focuses on the key role of direct local inspection and dynamic testing in the seismic assessment of the historic building.
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Determining the behavior of a structure estimated by means of finite elements analysis requires not only an in-depth knowledge of its geometry and dynamic properties but also an experimental validation to corroborate the adequacy of the characteristics of the structure. Most of the current structural identification techniques are based on linear methods that call for many measurement points and/or a relative simple structure. Complex structures are somewhat still an unexplored field due to the difficulties with the finite element method and the experimental corroboration of its results. This study presents the use of particle motion computation applied to each structural vibration mode to improve the identification of its dynamic properties, and its application to the Gothic Cathedral of Palma de Majorca (Spain).
Article
The dynamic identification of a historical masonry palace located in Benevento (Italy) has been carried out. The case study is representative of many buildings located in historic Italian centres. Since the building has been instrumented by the Department of Civil Protection with a permanent dynamic monitoring system, some of the recorded data, acquired in various operating conditions have been analysed with basic instruments of the Operational Modal Analysis in order to identify the main eingenfrequencies and vibration modes of the structure. The experimental results have been compared to the numerical outcomes provided by a detailed three-dimensional Finite Element (FE) model of the building where Soil–Structure Interaction (SSI) has been taken into account. The comparison of experimental vs. numerical frequencies and vibration modes of the palace evidenced the role exerted by the subsoil on the dynamic response of the building.
Article
Knowledge of the dynamic behavior of complex buildings subjected to near-fault earthquakes may be enriched by valuable information obtained through rapid on-site dynamic testing to aid in the design of appropriate retrofitting interventions. Through a case study, the paper demonstrates the enhancement in comprehension of the structural behavior obtained by means of a two-day testing campaign conducted on a complex building of the Engineering Faculty, Edifice A, which was heavily damaged in the 2009 L’Aquila earthquake. The on-site testing was carried out with a network of thirteen accelerometers opportunely located to identify the dynamic characteristics of the structure by means of ambient noise induced vibration. Enhanced Frequency Domain Decomposition (EFDD) and Stochastic Subspace Identification (SSI) output only-procedures were both used to identify the main modal parameters of two substructures of the building. The modal model was used to update a finite element numerical model representing small amplitude vibrations of the damaged structures. The direct comparison of the identified modal models with finite element models, in which damaged member locations are determined by on-site visual observations, has permitted to identify a model representative of the structural behavior of the building in the immediate post-earthquake conditions.
Article
In the process of preservation of ancient masonry structures, damage evaluation and monitoring procedures are particularly attractive, due to the modern context of minimum re- pair and observational methods, with iterative and step-by-step approaches. High-priority re- search issues related to damage assessment and monitoring are global non-contact inspection techniques, sensor technology, data management, diagnostics (decision making and simulation), dynamic (modal) analysis, self-diagnosing / self-healing materials, and prediction of early deg- radation. On these concerns, the present paper aims to assess damage in masonry structures at an early stage. Replicates of historical constructions were built in virgin state. Afterwards, progres- sive damage was applied and modal identification analysis was performed at each damage stage, aiming at finding adequate correspondence between dynamic behavior and internal crack growth. Accelerations and dynamic strains were recorded in many points of the replicates. Comparisons between different techniques based on vibrations measurements are made to evaluate different damage identification methods.
Article
The seismic response of the Mexico City Cathedral built of very soft soil deposits is evaluated by using motions recorded in various parts of the structure during several moderate earthquakes. This unique set of records provides significant insight into the seismic response of this and other similar historic stone masonry structures.Free-field ground motions are carefully compared in time and frequency domains with motions recorded at building basement. The dynamic characteristics of the structure are inferred from the earthquake records by using system identification techniques. Variation of seismic response for different seismic intensities is discussed. It is shown that, due to the soil–structure interaction, due to large differences between dominant frequencies of earthquake ground motions at the site and modal frequencies of vibration of the structure, and due to a particularly high viscous damping, seismic amplifications of ground motion in this and similar historic buildings erected on soft soil deposits are much smaller than that induced in most modern constructions. Nevertheless, earthquake records and analytical results show that several components of the structure such as its central dome and the bell towers may be subjected to local vibrations that significantly amplify ground motions. Overall, results indicate that in its present state the structure has an acceptable level of seismic safety. Copyright © 2008 John Wiley & Sons, Ltd.
Article
When performing vibration tests on civil engineering structures, it is often unpractical and expensive to use artificial excitation (shakers, drop weights). Ambient excitation on the contrary is freely available (traffic, wind), but it causes other challenges. The ambient input remains unknown and the system identification algorithms have to deal with output-only measurements. For instance, realisation algorithms can be used: originally formulated for impulse responses they were easily extended to output covariances. More recently, data-driven stochastic subspace algorithms which avoid the computation of the output covariances were developed. The key element of these algorithms is the projection of the row space of the future outputs into the row space of the past outputs. Also typical for ambient testing of large structures is that not all degrees of freedom can be measured at once but that they are divided into several set-ups with overlapping reference sensors. These reference sensors are needed to obtain global mode shapes. In this paper, a novel approach of stochastic subspace identification is presented that incorporates the idea of the reference sensors already in the identification step: the row space of future outputs is projected into the row space of past reference outputs. The algorithm is validated with real vibration data from a steel mast excited by wind load. The price paid for the important gain concerning computational efficiency in the new approach is that the prediction errors for the non-reference channels are higher. The estimates of the eigenfrequencies and damping ratios do not suffer from this fact.
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