Article
To read the full-text of this research, you can request a copy directly from the authors.

Abstract

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.

No full-text available

Request Full-text Paper PDF

To read the full-text of this research,
you can request a copy directly from the authors.

... The long-term monitoring of monuments confirmed the influence of environmental conditions for this type of structures as well, and various examples have been reported from several countries [11,[22][23][24][25][26][27][28][29][30][31]. Although the majority of them consist of stone/brick masonry buildings, earthen structures are not exempt from these effects either [32,33]. ...
... As for the latter, it has been shown that increasing wind actions can induce large tensile stresses in tall masonry buildings, which are likely to reduce their stiffness, thus their frequencies [46]. In some cases the environmental effects present a time lag as compared to the monitored quantity, that varies based on the physics of the phenomenon [32,33]. ...
... Finally, for the sa completeness, the two factors with the largest correlation (e.g., air temperature T and ative humidity RH) are combined into a single parameter, namely the absolute hum AH, according to the following formula: (g/m 3 ), and its correlation with the frequency values is also investigated. This parameter has used to analyse monitoring data from adobe historical buildings (e.g., [32,33]), whos namic response demonstrated to be strongly affected by humidity. However, for the sent case study, the T-AH combination does not produce a better correlation ( Figure l). ...
Article
Full-text available
Data-driven methodologies are among the most effective tools for damage detection of complex existing buildings, such as heritage structures. Indeed, the historical evolution and actual behaviour of these assets are often unknown, no physical models are available, and the assessment must be performed only based on the tracking of a set of damage-sensitive features. Selecting the most representative state indicators to monitor and sampling them with an adequate number of records are therefore essential tasks to guarantee the successful performance of the damage detection strategy. Despite their relevance, these aspects have been frequently taken for granted and little attention has been paid to them by the scientific community working in the field of Structural Health Monitoring. The present paper aims to fill this gap by proposing a multistep strategy to drive the selection of meaningful pairs of correlated features in order to support the damage detection as a one-class classification problem. Numerical methods to reduce the number of necessary acquisitions and estimate the performance of approximation techniques are also provided. The analyses carried out to test and validate the proposed strategy exploit a dense dataset collected during the long-term monitoring of an outstanding heritage structure, i.e., the Church of ‘Santa Maria de Belém’ in Lisbon.
... Since the Neolithic period (10,000-3,000 BC), adobe has been extensively used as an economical, flexible, readily available, and local construction material in various regions throughout the world (Brown and Clifton 1978;Houben and Avrami 2000;Blondet et al. 2011). Many historical monuments and buildings in Africa (e.g., Egypt), Europe (e.g., Spain, Italy, England, and Romania), Asia (e.g., China, Yemen, and Iran), North America (e.g., New Mexico in the US), and Latin America (e.g., Peru and Mexico) are built with adobe bricks (Rael 2009;Quagliarini et al. 2010;Blondet et al. 2011;Silveira et al. 2012;Zonno et al. 2019). Earthen buildings made of adobe bricks are still widely used, particularly in rural areas with a hot and arid climate. ...
... The main concerns associated with the structural integrity of historical and contemporary adobe buildings lay in their vulnerability to weathering, erosion, and loss of strength due to infiltration, seasonal drying-wetting cycles, and the capillary rise of groundwater (Zonno et al. 2019;Weldon et al. 2019). Among them, the durability of adobe walls against weathering depends on the shear strength. ...
... Email: m.monghasem@sutech.ac.ir degree of saturation. Adobe buildings are commonly popular in areas with hot and arid climates (Rael 2009;Quagliarini et al. 2010;Blondet et al. 2011;Silveira et al. 2012;Zonno et al. 2019), in which clayey materials, such as adobe, can experience large amounts of suction. The aforementioned factors signify the need for considering the role of matric suction and changes in the degree of saturation when assessing the mechanical behavior (e.g., shear strength) of adobe. ...
Article
Full-text available
Adobe has been extensively used as a viable construction material in various hot and arid climatic regions throughout the world for several centuries. Adobe bricks, primarily made out of clay, remain in an unsaturated state for the majority of their life span. These unsaturated bricks are vulnerable to weathering, erosion, cracking, and strength degradation due to changes in moisture and drying-wetting cycles imposed by climatic events and seasonal changes. However, limited information exists in the literature regarding the effect of suction and degree of saturation on the mechanical response of unsaturated adobe. The main objective of this study was to experimentally examine the effect of suction on the shear strength and dilatancy of the adobe used for the repair of a 1,500-year-old adobe castle, the Izad Khast Castle, in Central Iran. We tested the index, physical, mineralogical, and microstructural characteristics of the adobe. After determining the drying and wetting paths of the soil water retention curve (SWRC), we built and employed an osmotic direct shear device to evaluate the shear strength extensively and dilatancy of the adobe under various matric suctions (0, 200, 400, and 800 kPa) and vertical stresses (39, 66, and 122 kPa) without and with the application of drying-wetting cycles. The tested adobe exhibited a significant suction hardening with a brittle behavior along with the shear-induced dilation. Increasing suction prompted a notable rise in the effective angle of friction and a linear increase in dilatancy of the adobe. Applying drying-wetting cycles led to a less brittle response accompanied by a decrease in the peak shear strength. The findings offer new insight into the mechanical behavior of unsaturated adobe, which can contribute toward the preservation and maintenance of historical and contemporary adobe structures.
... 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. ...
... The influence of the environmental conditions in the dynamic structural responses of the churches was verified through the calculation of the coefficients of determination (R 2 ) for each of the measured variables when calculated without consideration of time lag between environmental variable and frequency. Detailed study about the time lag between dynamic properties of adobe structures and environmental parameters are reported in (Zonno et al. 2019a(Zonno et al. , 2019b. As shown in Table 3, the results indicate that, even if similitudes were visible in the previous analysis, there are no correlation between the environmental variables and the structural response (R 2 below 0.10 in the majority of the cases). ...
... The absolute humidity was next calculated aiming at exploring the relationship of a single environmental variable that integrates the information of ambient temperature and relative humidity with the long-term variations of natural frequencies. As reported in (Zonno et al. 2019a), the absolute humidity is defined as the mass of the water vapor in a certain volume, and may be calculated as a function of the ambient temperature and relative humidity according to Equation (1) (Bolton, 1980), where MM, V, R, T, and RH are the molecular mass of water, the analyzed volume (in this case V = 1 m 3 ), the gas constant, the temperature of gas in°C, and the relative humidity, respectively. ...
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.
... Since the Neolithic period (10,000-3,000 BC), adobe has been extensively used as an economical, flexible, readily available, and local construction material in various regions throughout the world (Brown and Clifton 1978;Houben and Avrami 2000;Blondet et al. 2011). Many historical monuments and buildings in Africa (e.g., Egypt), Europe (e.g., Spain, Italy, England, and Romania), Asia (e.g., China, Yemen, and Iran), North America (e.g., New Mexico in the US), and Latin America (e.g., Peru and Mexico) are built with adobe bricks (Rael 2009;Quagliarini et al. 2010;Blondet et al. 2011;Silveira et al. 2012;Zonno et al. 2019). Earthen buildings made of adobe bricks are still widely used, particularly in rural areas with a hot and arid climate. ...
... The main concerns associated with the structural integrity of historical and contemporary adobe buildings lay in their vulnerability to weathering, erosion, and loss of strength due to infiltration, seasonal drying-wetting cycles, and the capillary rise of groundwater (Zonno et al. 2019;Weldon et al. 2019). Among them, the durability of adobe walls against weathering depends on the shear strength. ...
... Email: m.monghasem@sutech.ac.ir degree of saturation. Adobe buildings are commonly popular in areas with hot and arid climates (Rael 2009;Quagliarini et al. 2010;Blondet et al. 2011;Silveira et al. 2012;Zonno et al. 2019), in which clayey materials, such as adobe, can experience large amounts of suction. The aforementioned factors signify the need for considering the role of matric suction and changes in the degree of saturation when assessing the mechanical behavior (e.g., shear strength) of adobe. ...
... The studies made by Ramos, et al. (Ramos 2007;Ramos et al. 2006), Oyarzovera, et al. (Oyarzo-vera, Ingham, andChouw 2014) and Masciotta, et al. (Masciotta et al. 2014) in stone masonry historical structures show that vibration-based damage detection is possible since their modal parameters are sensitive to damage. Recent studies regarding the long-term structural response of historical adobe constructions indicate that the modal parameters are much affected by environmental conditions, which makes more difficult the possibility of accurate detection of changes associated to structural damage (Zonno et al. 2018(Zonno et al. , 2019a. ...
... In this case, variations of almost 60% were registered (varying from 27% to 90%). An attenuation of variations is again registered for the last 5 days of monitoring period (Zonno et al. 2019a). ...
Article
Structural Health Monitoring (SHM) has demonstrated to be a fundamental tool for detecting damage in early stages in existent civil engineering structures. This paper explores the accuracy of vibration-based SHM for identifying the existence of damage in adobe constructions, a widespread structural system but on which limited experimental and numerical applications of the technique are available. Two damage detection methodologies are investigated: (i) Autoregressive Models to predict the structural dynamic response taking into account the environmental parameters as input; and (ii) Principal Component Analysis to detect patterns and anomalies in this response without the need of information about environmental conditions. The results of the laboratory tests on a real scale adobe wall positively indicate the capabilities of these two methodologies to accurately identify damage. They also evidence the importance of monitoring several modes as their sensitivity to damage depends on damage location itself. Furthermore, the application of these two damage detection methodologies in a real case study related to the long-term monitoring of a 16th Century adobe church allowed confirming the building safe condition during almost two years of monitoring period, as well as the absence of damage after a 5.2Mw earthquake.
... Among the environmental factors that have the greatest impact on modal frequency, there is a consensus that temperature is the main explanatory variable in medium and tall concrete buildings [9][10][11][12][13][14][15][16][17][18][19][20]. The relationship between modal frequency and both internal and external temperature is complex, due to the internal gradient and the exposure of the structural elements that control the modal parameters [21,22]. This highly non-linear interaction demands robust nonlinear models in order to predict the system's state within a low error threshold. ...
Article
For Civil Engineering System Structural Health Monitoring (SHM), damage identification is typically based on the observation of appropriate response features. A commonly selected feature is the variation of modal frequency due to its high sensitivity to global damage. However, this parameter also has a high sensitivity to variables unrelated to damage, such as the weather and the structure’s usage. This article focuses on the application of Recurrent Neural Networks (RNN) with Long-Short Term Memory (LSTM) blocks to modal tracking in medium-rise buildings, a case study for which there is very little literature despite being one of the most common building types in urban areas. RNN with LSTM blocks are trained to characterize the environmental trend in the modal frequency to identify the most critical variables and to develop models than can be used to detect changes of state or damage. The models are fed with the recent history of the external temperature, sun position and the modal frequency itself. The performance of these models is evaluated in two different ways: for a variable size of the training set of real data and for scenarios with segments in which the modal response is not known at all instants, a typical situation in real structures. A practical application of this approach in a real medium-rise building is presented, showing that these models are capable of capturing with high precision the annual evolution of the modal frequency and performing well even on a daily scale, making it suitable for damage detection. For the cases in which the modal response is regularly identified and tracked, the characterization has a high performance when tracking single modal frequency or several frequencies with a single model. The models are robust for periods where data is not available but quickly deteriorate if this period extends for several days.
... 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. In the case of earthen existing buildings, the authors show in [11][12] how thermohygrometric variations can produce significative changes in natural frequencies at long and short scales because the environmental parameters are time-dependent and non-uniform quantities. ...
... The frequency-temperature model is developed using the previously classified training period data. To improve the fit, the periodical variations associated with the winter-summer cycle and the day-night cycle are treated separately, as used in other works [33][34][35]. In this work, the frequency average of the last week is considered as the seasonal component and the difference between this average and its instantaneous value as the daily component. ...
Article
In Structural Health Monitoring (SHM), the instrumentation policies for buildings usually require large numbers of high-resolution sensors. The relatively high economic cost for the sensors and their interconnecting cables has discouraged the widespread application of SHM. For modal analysis, small number of sensors means low spatial resolution of mode shapes, which limits the possibility of differentiating between close frequency modes in a single measurement and between consecutive measurements on a continuous monitoring system. In this study, we try to overcome this limitation, particularly on the tracking component of SHM, with the aid of a predictive numerical model based on the effect of the ambient temperature on the modal frequency. To validate this hypothesis, we test it on a real building, monitored with a small number of low-resolution sensors. The methodology’s performance is evaluated during normal conditions, rainfall and also after the damaging Chile Maule earthquake (Mw of 8.8), proving to be effective for tracking purposes. For this building, the sensitivity of the mode shape and damping to the environment is also studied, showing a very low sensitivity as compared to the frequency. This validates the simpler temperature – frequency model.
... The use of dynamic-based monitoring of architectural heritage is widespread in the last few years (Azzara et al. 2018;Elyamani et al. 2018;Gentile, Ruccolo, and Saisi 2019;Masciotta et al. 2016;Ubertini et al. 2017;Zonno et al. 2019). Most of the activity regards dynamic identification under operational conditions. ...
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.
... In this context, vibration-based continuous dynamic monitoring systems are becoming popular tools for automatically identifying anomalies in the structural dynamic behavior following small earthquake-induced damages, thus triggering preventive conservation measures with the purpose of avoiding damage accumulation during a seismic sequence. During the last decades, several contributions can be found in the literature regarding the effectiveness of continuous dynamic monitoring both in detecting earthquake-induced damages and for investigating the effects of changing environmental conditions on the modal parameters of historical constructions [6,7,8,9,10,11,12]. Unfortunately, the localization of damages by means of output-only information provided by dynamic monitoring systems often requires the continuous tuning of numerical models based on identified modal parameters, which in most of the cases results in excessive computational efforts. ...
... Preventive conservation against material degradation and natural hazards is a societal priority, as well as a scientific and technical challenge, especially with reference to Cultural Heritage (CH) structures. In this context, diagnostic and monitoring activities are crucial for structural health assessment (Pierdicca et al., 2016;Clementi et al. 2017Clementi et al. , 2018Ceravolo et al., 2017;Liu et al., 2017;Masciotta et al., 2017;Saisi et al., 2018;Ubertini et al., 2018;Zonno et al. 2019aZonno et al. , 2019b) and a highly multidisciplinary approach considering different methods and technologies is often mandatory (Costanzo et al., 2015;Masciotta et al., 2016;Dall'Asta et al., 2019;Ludeno et al., 2019;Pierdicca et al., 2019). In the last decade, new challenges in structural monitoring are involving remote sensing techniques, such as satellite synthetic aperture radar (SAR) interferometry (InSAR), which is a powerful technique able to measure slow ground deformations, due to subsidence, landslides, earthquakes and volcanic phenomena, from images acquired by SAR satellites orbiting at more than 500 km above the ground. ...
Article
The paper presents an overview of the results of diagnostic and monitoring activities carried out in the last years through satellite radar interferometry (2011-2016) and in situ measurements (2017-2019) in the historical city of Gubbio, Italy. The study is aimed at contributing to understanding the potential of remote sensing technologies in measuring complex deformation phenomena in historic buildings, such as those caused by soil-structural interaction and earthquakes, considering the monumental Consoli Palace and the Town Walls as case studies. The research activities have been carried out within the European HERACLES project, funded in the framework of Horizon 2020 and aimed at proposing novel diagnostic monitoring solutions for enhancing heritage resilience against various types of hazards. Particular attention is focused on the cross-correlation of the outputs of satellite radar interferometry and in-situ structural monitoring data aimed at achieving engineering meaningful results supporting decision making and proactive interventions.
... The disadvantage of adobe is its deterioration in the face of weathering factors such as rain and wind. There are, however, a few innovations that provide greater resistance in adobe stabilization, such as a cover of latex, lime or fermented fertilizer mixtures [15][16][17]. ...
Article
Full-text available
The scope of this work covers a proposal for the implementation of sustainable, low-cost, environmentally friendly, and affordable housing for low-income people. This paper aims to address the current housing issues, namely that many people lack decent housing and that the built houses are usually of a poorly sustainable nature. The work consists of three main parts: an evaluation of housing sustainability, measurement of parameters related to their internal comfort and a simulation of thermal enclosure with the COMSOL Multiphysics® software. An important objective is to propose a sustainability assessment format, which, besides being explained in detail, is presented in a percentage scale for ease of understanding. This work seeks a methodology for evaluating the level or degree of sustainability for the construction and inhabitation stages of housing. Using a prototype constructed with polyethylene terephthalate (PET) bottles, temperature and humidity were measured. There was a contrasting behavior of these two parameters, which tended towards an inverse behavior, except on cloudy or rainy days. The roof of the prototype contained some waste materials that provided thermal insulation: galvanized steel, polyethylene bags for upcycling as waterproofing, PET bottles, soil and endemic plants (green roof). The results obtained in the simulation are in accordance with the real internal behavior of the prototype.
... Thus, the implementation of a shorter period evaluation (mainly at a daily level) is relevant to fully understand the influence of environmental conditions changes. In the present study, the results indicate that the temperature seems to have a stronger influence on the daily variations of the modal parameters than the relative humidity, which is also reported in [32,33,57]. For this reason, the additional short-term and daily analyses were performed using only the temperature as the main environmental variable. ...
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.
Chapter
Adobe constructions are widely used worldwide as low-cost vernacular buildings and also as monuments and historical constructions. Beside low cost these materials have excellent thermal and acoustic properties. Some challenges of this material involves durability and high vulnerability to seismic motions due to its relatively high weight and brittleness. To improve safety levels of existing adobe structures it is often necessary to strengthen or retrofit them based on a structural characterization. The structural characterization requires assessment of the in situ condition, geometry, engineering properties of existing adobe construction and buildings using minimal to no intrusion. In this chapter we present a general overview of commonly used NDT and MDT methods for the assessment of existing adobe construction to obtain information such as: detailed geometry information, damage mapping, and multi-scale mechanical and physical characterization. Additional to literature review summarizing different applications of NDT and MDT, this chapter presents four case studies related to projects in Peru recently performed by the research group led by the first author. The descriptions and results of NDT and MDT tests carried out at these case studies highlight how the use of several NDT and MDT methodologies complement each other and allow a suitable multi-scale characterization of existing adobe structural systems, that can successfully be used for the diagnosis, and design of intervention and retrofit measures as needed.
Article
Considering the challenges imposed by the current movement towards green development, earth construction appears to offer promising possibilities for improving thermal comfort, energy consumption and indoor humidity regulation. However, the difficulties in predicting the behaviour of earth as a construction material is an obstacle to the development of this technique. The principal objective of this study is to establish the scientific bases needed to predict its hygroscopic and mechanical behaviour as a function of the relative humidity that is one of the main factors controlling the home confort. For this purpose, it is necessary to find correlations between the variability of the soils (density, pore size distribution, chemical and mineralogical composition) and the hygromechanical behaviour of the earth bricks (adsorption, hydric buffering and compressive strength). The results, in terms of hydric and mechanical behaviour specific to each brick, show that the behaviour of this material depends on several factors, namely, the SiO2/Al2O3 ratio, the porosity rate, the pore size distribution, the nature of the clay minerals, and their content.
Article
Full-text available
This paper presents the results of a numerical study using the finite element method to assess the effect of wall thickness and a moist region along the wall base on the out-of-plane lateral stability of adobe walls. The models consisted of cantilever unreinforced adobe walls with a thickness of 25 cm, 30 cm, and 40 cm. Numerical analyses were performed for four lengths (L) of the moist region and for dry walls. The moist region was modelled with material characteristics corresponding to partially saturated and nearly saturated adobe. The results showed the detrimental effect of moisture along the lower portion of the wall on the out-of-plane lateral strength. The out-of-plane lateral strength reduction ratio dropped significantly as L increased. A high slenderness ratio was found to be critical for cantilever adobe walls when L extended beyond half of the wall length. The results provided insights concerning the role of wall thickness in the stability against overturning.
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.
Article
Full-text available
Temperature variation has been widely demonstrated to produce significant effect on modal frequencies that even exceed the effect of actual damage. In order to eliminate the temperature effect on modal frequency, an effective method is to construct quantitative models which accurately predict the modal frequency corresponding to temperature variation. In this paper, principal component analysis (PCA) is conducted on the temperatures taken from all embedded thermocouples for extracting input parameters of regression models. Three regression-based numerical models using multiple linear regression (MLR), back-propagation neural network (BPNN), and support vector regression (SVR) techniques are constructed to capture the relationships between modal frequencies and temperature distributions from measurements of a concrete beam during a period of forty days of monitoring. A comparison with respect to the performance of various optimally configured regression models has been performed on measurement data. Results indicate that the SVR exhibits a better reproduction and prediction capability than BPNN and MLR models for predicting the modal frequencies with respect to nonuniformly distributed temperatures. It is succeeded that temperature effects on modal frequencies can be effectively eliminated based on the optimally formulated SVR model.
Article
Full-text available
The present paper shows the vibrational characterization tests of a clay brick heritage construction from XIX century, the Nossa Senhora das Dores Church, placed in Sobral, Brazil. In this study the calibration of the 3D finite element numerical model of the church was performed through ambient vibrational testing using the first three natural frequencies identified. The obtained results, namely the natural frequencies identified, and the calibrated model intends to give a contribute for understanding of the structural behavior of the Brazilian heritage constructions, and introduces relevant information for be used for safety assessment of the church along the time.
Article
Full-text available
Earth has been a traditional building material to construct structures in many different continents. In particular, adobe buildings are widely diffused in South America, and in Peru where form part of the cultural identity of the nation. Nowadays, the knowledge of existing adobe buildings is far from a complete understanding of the constructive system and a structural health monitoring (SHM) can quantify and reduce uncertainties regarding their structural performance without causing damage to the buildings. In this process, the implementation of automatic tools for feature extraction of modal parameters is desirable. In particular, the automation is important because, during a long-term monitoring, a huge amount of data is recorded and the direct check of the data of the user is not possible. The present work is focused on the development of an automated procedure for managing the results obtained from the parametric identification method, in particular from the Data-Driven Stochastic Subspace Identification method, which requires an automatic interpretation of stabilization diagrams. The work presents a fully automated modal identification methodology based on the following steps: (i) digital signal pre-processing of the recorded data; (ii) modal parameter identification using models with varying dimensions; (iii) automatic analysis of the stabilization diagram with the application of soft and hard validation criteria and the use of hierarchical clustering approach to eliminate the spurious modes; and (iv) automatic choice of the most representative values of the estimated parameters of each clustered mode: natural frequency, damping and mode shape. The developed algorithm was firstly tested with an inverted steel pendulum to check the accuracy and sensitivity, and subsequently, an earthen wall built in PUCP Structure Laboratory was analysed to determine its dynamic behaviour. The developed algorithm shows high percentages of detected frequencies and high sensitivity to the environmental and structural changes.
Article
Full-text available
The response of the San Pietro monumental bell-tower located in Perugia, Italy, to the 2016 Central Italy seismic sequence is investigated, taking advantage of the availability of field data recorded by a vibration-based SHM system installed in December 2014 to detect earthquake-induced damages. The tower is located about 85 km in the NW direction from the epicenter of the first major shock of the sequence, the Accumoli Mw6.0 earthquake of August 24th, resulting in a small local PGA of about 30 cm/s², whereby near-field PGA was measured as 915.97 cm/s² (E–W component) and 445.59 cm/s² (N–S component). Similar PGA values also characterized the two other major shocks of the sequence (Ussita Mw5.9 and Norcia Mw6.5 earthquakes of October 26th and 30th, respectively). Despite the relatively low intensity of such earthquakes in Perugia, the analysis of long-term monitoring data clearly highlights that small permanent changes in the structural behavior of the bell-tower have occurred after the earthquakes, with decreases in all identified natural frequencies. Such natural frequency decays are fully consistent with what predicted by non-linear finite element simulations and, in particular, with the development of microcracks at the base of the columns of the belfry. Microcracks in these regions, and in the rest of tower, are however hardly distinguishable from pre-existing ones and from the physiological cracking of a masonry structure, what validates the effectiveness of the SHM system in detecting earthquake-induced damage at a stage where this is not yet detectable by visual inspections.
Article
Full-text available
Long-term dynamic monitoring of the masonry façade of Palazzo Ducale known as Doge’s palace in Venice, Italy was performed from September 2010 to October 2012. This article demonstrates the results of preliminary analysis on the data set of the first 12-month long monitoring campaign for out-of-plumb dynamic responses of the medieval façade of the monument. The aim of the analysis of the dynamic signals is to validate the data set and investigate dynamic characteristics of the vibration signature of the historical masonry wall in the long-term. Palazzo Ducale is a heavily visited heritage due to its high cultural importance and architectural value. Nevertheless, little is known about the dynamic behaviour of the double-leaf masonry façade. In this study, the dynamic properties of the structure are presented by dynamic identification carried out with the effect of the ambient vibration measured at four different locations on the façade and portico level. The trend and intensity of the vibration at each measurement locations are identified over the year. In addition, the issue on eliminating the noise blended in the signals for reliable analysis are also discussed.
Article
Full-text available
The paper discusses the monitoring-based approach unfolded to evaluate the health condition of a heritage structure in Portugal. An extensive experimental campaign, including geometric survey, visual inspections, damage diagnosis, monitoring and control, is carried out to support and evaluate the actions undertaken to re-establish the structural strength. The paper focuses on the analysis of case-specific static and dynamic parameters deemed representative of the structural behaviour and highlights the benefits associated with the implementation of a monitoring-weighed methodology in terms of diagnostics of the system’s vulnerabilities as well as control of the effectiveness of the adopted consolidation measures. The results demonstrate the feasibility and suitability of this systematic experimental approach for the non-invasive assessment of the structural fitness of built cultural heritage.
Article
Full-text available
Changes of modal frequencies induced by temperature variation can be more obvious than those caused by structural damage, which will lead to the false damage identification results. Therefore, quantifying the temperature effect on modal frequencies is a critical step to eliminate its interference in damage detection. Due to the nonuniform and time-dependent characteristics of temperature distribution, it is insufficient to obtain the reliable relationships between temperatures and modal frequencies using temperatures in air or at surface. In this paper, correlations between measured temperatures (air temperature, surface temperature, mean temperature, etc.) and modal frequencies for the slab and beam are comparatively analyzed. And the quantitative models are constructed considering nonuniform temperature distribution. Firstly, the reinforced concrete slab and beam were constructed and placed outside the laboratory to be monitored. Secondly, the correlation coefficients between modal frequencies and three kinds of temperatures are calculated, respectively. Thirdly, simple linear regression models between mean temperature and modal frequencies are established for the slab and beam. Finally, five temperature variables are selected to construct the multiple linear regression models. Prediction results reveal that the proposed multiple linear regression models possess favorable accuracy to quantify the temperature effect on modal frequencies considering nonuniform temperature distribution.
Article
Full-text available
The paper reports a wide overview of the scientific activities on Structural Health Monitoring (SHM) in Italy. They are classified on three different conceptual scales: national territory (macro); regional area (medium); single structure (small). In the latter case differences have been pointed out between permanent installation and short-term experimental campaigns. A particular focus has been dedicated to the applications devoted to cultural heritage which have an important historic, strategic and economic value for Italy. Two specific cases, the first related to the permanent monitoring of an historical Basilica and the second regarding the dynamic testing of a modern structure, have been presented as a basis for a general discussion.
Article
Full-text available
The architectural heritage in the world represents a fundamental resource and a sign of the national cultural background. Its maintenance and preservation require a balance between the structural safety needs and the respect for their architectural and cultural value. Structural health monitoring (SHM) is increasingly emerging as a unique tool to achieve such a balance, through a proper combination of traditional and innovative techniques. This paper presents some recent experiences of SHM applied to the historical heritage in Italy, discussing relevant tools and reporting some of the most significant case studies.
Article
Full-text available
The work presents the inter-disciplinary multi-year project focused on the permanent seismic monitoring of a historical structure, the Basilica S. Maria di Collemaggio, by means of an advanced wireless sensor network. Considered among the architectural masterpieces of the Italian Romanesque, the structural behaviour of the monumental masonry church is strongly debated after the heavy damages and the partial collapse that occurred during the 2009 L’Aquila earthquake. From the perspective of information technology, critical issues in the wireless data acquisition and communication are analysed. The sensor network design, deployment and performance are discussed with respect to the high-demanding service requirements—as well as the non-negligible management costs—specifically related to the long-term monitoring of a monumental masonry structure in a seismic area. From the perspective of experimental signal analysis, the acceleration data collected during a 3-year period of seismic monitoring are analysed in the frequency and time domains. The results allow the clear detection of complex interactions between the masonry structures and some of the temporary protective installations. Stochastic subspace identification procedures are applied, with critical analysis of their effectiveness in the assessment of reliable modal models from the building response to real seismic events. Finally, the robustness of the modal identification obtained from the structural responses to different near- and far-field micro-earthquakes is discussed, with the aid of numerical models of the damaged and protected church configuration.
Article
Full-text available
The shift of modal parameters induced by temperature fluctuation may mask the changes of vibration properties caused by structural damage and result in false structural condition identification. Thoroughly understanding the temperature effects on vibration properties of long-span bridges becomes an especially important issue before vibration-based damage detection methodologies are applied in real bridges. This paper presents an overview of current research activities and developments in the field of correlations between temperatures and vibration properties of long-span bridges. The theoretical derivation methods using classical structural dynamics and closed-form formulations are first briefly introduced. Then the trend analysis methods that are intended to extract the degree of variability in vibration property under temperature variation for different bridges by numerical analysis, laboratory test, or field monitoring are reviewed in detail. Following that, the development of quantitative models to quantify the temperature influence on vibration properties is discussed including the linear model, nonlinear model, and learning model. Finally, some promising research efforts for promoting the study of correlations between temperatures and vibration properties of long-span bridges are suggested.
Article
Full-text available
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
Article
Full-text available
Rammed earth construction is attracting a renewed interest throughout the world thanks to its “green” characteristics in the context of sustainable development. Several studies have been carried out to investigate this material and evaluate its durability along with its mechanical, thermal and earthquake capacities. This paper presents a study on the parameters needed for the seismic design of rammed earth buildings in accordance with current earthquake standards. First, the dynamic parameters of buildings such as natural frequencies and damping ratios–which were necessary to determine the equivalent static seismic force–were identified using in-situ dynamic measurements. Then, these experimental values were compared with the values calculated by empirical formulas suggested in Eurocode 8 to demonstrate that these formulas were applicable for the cases of rammed earth structures. Then, modeling was done to find a simple suitable model for rammed earth structures. Laboratory experiments were developed to measure the Poisson’s ratio which was necessary for the models. The results provided by the shear-beam model were close to that of in-situ experiments, which showed a shearing behavior of rammed earth structures. Elements which influenced the dynamic behavior of this structural type were also discussed. Understanding the dynamic characteristics of rammed earth structures will help engineers in their design of new rammed earth buildings but also in earthquake analyses of existing rammed earth buildings.
Article
Full-text available
It is a normal practice to consider the reduction of modal frequencies as an indicator for structural damage but some long-term monitoring studies revealed that the structural modal frequencies exhibited substantial seasonal variation without evidence of structural damage. Therefore, in order to perform reliable and consistent assessment on the health condition of civil engineering infrastructures, it is an indispensable task to quantify the modal frequency fluctuation induced by change of ambient conditions, such as temperature and humidity. In other words, it is necessary to distinguish the inevitable ambient interference from the abnormal changes due to structural damage and deterioration. In this paper, one-year daily measurement of a 22-storey reinforced concrete building is utilized to trace the variation of its modal frequencies, which are identified using the Bayesian spectral density approach with the ambient vibration data. Then, the Timoshenko beam model is considered to construct the mathematical model for the modal frequency–ambient condition relationship. Since the Timoshenko beam model incorporates both the shear and flexural deformation, it is appropriate for the behavior of buildings with different aspect ratios and configurations. Finally, Bayesian analysis is conducted to quantify the uncertain parameters in the modal frequency–ambient condition model. Results show that explicit consideration of the ambient temperature and relative humidity is essential for long-term structural health monitoring.
Article
Full-text available
Continuous monitoring of structural vibrations is becoming increasingly common as sensors and data acquisition systems become more affordable, and as system and damage identification methods develop. In vibration-based structural health monitoring, the dynamic modal parameters of a structure are usually used as damage-sensitive features. The modal parameters are often sensitive to changing environmental conditions such as temperature, humidity, or excitation amplitude. Environmental conditions can have as large an effect on the modal parameters as significant structural damage, so these effects should be accounted for before applying damage identification methods. This paper presents results from a continuous monitoring system installed on the Dowling Hall Footbridge on the campus of Tufts University. Significant variability in the identified natural frequencies is observed; these changes in natural frequency are strongly correlated with temperature. Several nonlinear models are proposed to represent the relationship between the identified natural frequencies and measured temperatures. The final model is then validated using independent sets of measured data. Finally, confidence intervals are estimated for the identified natural frequencies as a function of temperature. The ratio of observed outliers to the expected rate of outliers based on the confidence level can be used as a damage detection index.
Article
Full-text available
The paper addresses two complex case studies of modal and structural identification of monuments in Portugal: the Clock Tower of Mogadouro and the Church of Jerónimos Monastery, in Lisbon. These are being monitored by University of Minho with vibration, temperature and relative air humidity sensors. Operational modal analysis is being used to estimate the modal parameters, followed by statistical analysis to evaluate the environmental effects on the dynamic response. The aim is to explore damage assessment in masonry structures at an early stage by vibration signatures, as a part of a health monitoring process that helps in the preservation of historical constructions. The paper presents the necessary preliminary dynamic analysis steps before the monitoring task, which includes installation of the monitoring system, system identification and subsequent FE model updating analysis, automatic modal identification and investigation of the influence of the environment on the identified modal parameters.
Article
The estimation of modal parameters is a critical requirement in structural health monitoring, damage detection, design validation, among other topics. The most prevalent methodology for manual identification is via an interpretation of a stabilization diagram. A density-based algorithm for automatically interpreting this type of diagram is proposed. The method employs three stages of interpretation. First, hard criteria are used to discard distinct spurious modes. Second, a density-based algorithm, Ordering Points to Identify the Clustering Structure (OPTICS), is used to cluster data. Finally, the modal parameters are selected taking into account the density distribution of the clustered values. Automation on the procedure is proposed, tested and applied to the vibration measurements of a building structure that has been continuously monitored since 2009. The results indicate a satisfactory interpretation, despite the low signal-to-noise ratios, the effect of induced electric noise, the low density of the sensors, different ambient conditions, and the occurrence of earthquake events.
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.
Article
The paper presents a damage assessment strategy suitable to historic masonry towers. The methodology is exemplified using the data collected in the continuous dynamic monitoring of the San Vittore bell-tower (Arcisate, Northern Italy). The proposed damage assessment procedure aims not only at detecting the occurrence of structural anomalies, but also at localising the damage in the investigated structure. After a brief description of the tower and past diagnostic survey (including ambient vibration tests and Finite Element modelling), the results of the continuous dynamic monitoring are highlighted and the effect of temperature on automatically identified resonant frequencies is discussed. Subsequently, regression models based on Principal Component Analysis are applied in order to filter out the fluctuations caused by the environmental effects on the identified resonant frequencies. The damage detection and damage localisation issues are then addressed by using novelty analysis tools. The effectiveness of the proposed strategy is demonstrated through the detection and localisation of realistic damage scenarios simulated with the baseline Finite Element model. Specifically, the damage localisation has been tackled by using the “cleaned” modal properties within a continuous Finite Element model updating scheme.
Article
Health assessment of historical buildings by means of monitoring systems is for sure a fundamental step to preserve architectural heritage, especially for countries as Italy, rich in ancient monuments. Events such as earthquakes or severe weather phenomena constitute a major risk for these buildings because of their age and the related weakness to sustain exceptional excitations. The availability of a continuous, real time and automatic structural health monitoring system is considered a useful tool for early detection of a potentially dangerous situation for the structure and its occupants. The choice of the best measurement strategy provided by the monitoring system is crucial: a compromise must be found between the need of information, complexity of the measuring system and the related costs. Due to the difficulty in modelling most historical structures, it is a hard task to fix proper and safe limits relying on model-generated predictions only. The availability of long-term records of the structural response can help get this goal, not just relying on models, but also detecting changes in some parameters obtained from time records. This paper presents a challenging example: the structural health monitoring of the Duomo di Milano main spire during and after restoration.
Article
The paper summarizes the conceptual development of a vibration-based strategy suitable to the structural health monitoring of ancient masonry towers and exemplifies its application in the continuous dynamic monitoring of the tallest historic tower in Mantua, Italy. The presented approach is based on the installation of low-cost monitoring systems (consisting of few accelerometers and temperature sensors) and on the combined use of automated operational modal analysis, regression models to mitigate the environmental effects on identified natural frequencies and multivariate statistical tools to detect the occurrence of abnormal structural changes. The application of the adopted strategy to 15 months of continuously collected experimental data: (1) highlighted the effect of temperature on the automatically identified natural frequencies; (2) demonstrated the practical feasibility of damage detection methods based on natural frequency shifts; (3) provided a clear evidence of the possible key role of continuous dynamic monitoring in the preventive conservation of historic towers.
Article
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.
Article
Continuously identified natural frequencies of vibration can provide unique information for low-cost automated condition assessment of civil constructions and infrastructures. However, the effects of changes in environmental parameters, such as temperature and humidity, need to be effectively investigated and accurately removed from identified frequency data for an effective performance assessment. This task is particularly challenging in the case of historical constructions that are typically massive and heterogeneous masonry structures characterized by complex variations of materials' properties with varying environmental parameters and by a differential heat conduction process where thermal capacity plays a major role.
Article
The preservation and risk mitigation of built cultural heritage require the use of reliable tools which enable to give a better insight into the complex behaviour of these structures, by providing a correct diagnosis of their health conditions, and to identify potential vulnerabilities in order to prevent the risk of damage and to design in advance adequate retrofit solutions. The present paper describes an extensive experimental/numerical investigation campaign carried out on the Church of Monastery of Jerónimos in Lisbon in accordance with an iterative multidisciplinary approach and with the purpose of assessing the health state of one of the most prominent Portuguese monument, in light of future prevention actions. Special stress is given to the diagnostic procedure which includes and details in situ and laboratory testing, dynamic identification, continuous structural health monitoring and analysis of environmental effects on the static and dynamic behaviour of the church. The structural performance of the temple under conditions of gravity loading is analysed as well and potential collapse mechanisms are identified. The results are compared with the actual response of the temple allowing to evaluate its safety level.
Article
In the last decades the need for an effective seismic protection and vulnerability reduction of cultural heritage buildings and sites determined a growing interest in structural health monitoring (SHM) as a knowledge-based assessment tool to quantify and reduce uncertainties regarding their structural performance. Monitoring can be successfully implemented in some cases as an alternative to interventions or to control the medium- and long-term effectiveness of already applied strengthening solutions. The research group at the University of Padua, in collaboration with public administrations, has recently installed several SHM systems on heritage structures. The paper reports the application of monitoring strategies implemented to avoid (or at least minimize) the execution of strengthening interventions/repairs and control the response as long as a clear worsening or damaging process is detected. Two emblematic case studies are presented and discussed: the Roman Amphitheatre (Arena) of Verona and the Conegliano Cathedral. Both are excellent examples of on-going monitoring activities, performed through static and dynamic approaches in combination with automated procedures to extract meaningful structural features from collected data. In parallel to the application of innovative monitoring techniques, statistical models and data processing algorithms have been developed and applied in order to reduce uncertainties and exploit monitoring results for an effective assessment and protection of historical constructions. Processing software for SHM was implemented to perform the continuous real time treatment of static data and the identification of modal parameters based on the structural response to ambient vibrations. Statistical models were also developed to filter out the environmental effects and thermal cycles from the extracted features.
Article
SUMMARYA practical view is provided on the integration of electronic instrumentation, data acquisition, and software development systems applied to the analysis of pathological structural processes. This system will enable researchers to remotely monitor constructions; compile a register of historical data, creating files for postprocessing; and establish computer-based protocols for evaluation of information, defining automatic alarms when the monitored data exceed preset limit values. This integration is based on the implementation of a remote terminal unit architecture in an industrial PC along with some other elements, namely, the following: suitable data acquisition cards for the type of sensors used, which continuously collect the data the sensors gather; the installation of an application server that periodically communicates with the system, extracting data while guaranteeing persistence; and finally, a web server, which provides remote access to both the data themselves and the system configuration, using a client application developed in JavaFX, a platform for developing rich Internet applications. As an example of the integration, the architecture of a system deployed in a Church in Comillas, Spain, is shown. The work carried out related to the register of existing damage is reported in order to explain the choice of the zones for deployment of the monitoring devices as well as the tasks involved in the installation of the sensors and other devices. Finally, the evolution is presented of the measurements taken during more than 1.5 years of monitoring, as well as their validation through comparison with those obtained by discrete in situ measurement. Copyright © 2015 John Wiley & Sons, Ltd.
Article
A structural health monitoring (SHM) network was installed during the construction of a 56-story frame-wall concrete building with a height of 196 m. The SHM network recorded the vibrations produced by ambient, construction, and earthquake excitations. The vibrations were used to identify the natural periods, mode shapes, and damping ratios of the structure every 10 min for 6 consecutive months and at five specific stages of the construction process over a two-year period. The identified modal parameters were used to validate the construction process and the computer design model by comparing different adaptive computer models that correspond to the progress in construction. Maximum differences of 14% between measured and analytical model natural period were obtained, and correlation to modal shapes were close to 95%, which indicates a good approximation of the predictive design computer model. The experimental techniques also allowed for the direct measurement of the energy dissipation properties of the building. For the low amplitude vibrations, the modal damping ratio ranges from 0.7 to 1.6% for the largest natural periods. The occurrence of the 2010 Central-South Chile earthquake (magnitude Mw=8.8) also allowed for the comparison of the dynamic properties before and after an extreme loading event. A visual inspection of the building indicates an acceptable correlation between the minor damage observed and changes in the modal parameter values. The continuous monitoring of the dynamic properties of this permanently changing building proves to be an excellent tool for the verification of design models and quality assurance in construction control.
Article
This study focuses on how to exploit long-term monitoring data of structural strain for analytical modeling of multimodal rainflow-counted stress spectra by use of the method of finite mixture distributions in conjunction with a hybrid mixture parameter estimation algorithm. The long-term strain data acquired from an instrumented bridge carrying both highway and railway traffic is used to verify the procedure. A wavelet-based filtering technique is first applied to eliminate the temperature effect inherent in the measured strain data. The stress spectrum is obtained by extracting the stress range and mean stress from the stress time histories with the aid of a rainflow counting algorithm. By synthesizing the features captured from daily stress spectra, a representative sample of stress spectrum accounting for multiple loading effects is derived. Then, the modeling of the multimodal stress range is performed by use of finite mixed normal, lognormal, and Weibull distributions, with the best mixed distribution being determined by the Akaike's information criterion (AIC). The joint probability density function (PDF) of the stress range and the mean stress is also estimated by means of a mixture of multivariate distributions. It turns out that the obtained PDFs favorably fit the measurement data and reflect the multimodal property fairly well. The analytical expressions of PDFs resulting from this study would greatly facilitate the monitoring-based fatigue reliability assessment of steel bridges instrumented with structural health monitoring (SHM) system. DOI: 10.1061/(ASCE)EM.1943-7889.0000313. (C) 2012 American Society of Civil Engineers.
Article
The Gabbia Tower, about 54.0 m high and dating back to the XIII century, is the tallest tower in Mantua, overlooking the historic centre listed within the UNESCO Heritage. After the seismic sequence of May 2012 in Italy, an extensive research program was carried out to assess the structural condition of the tower. The post-earthquake investigation (including direct survey, historic and documentary research, testing of materials and ambient vibration tests) highlighted the poor state of preservation of the upper part of the building and suggested the installation of a dynamic monitoring system to evaluate the response of the tower to the expected sequence of far-field earthquakes and check the possible evolution of the structural behavior. After a brief description of the tower and the post-earthquake survey, the paper presents the results of the continuous dynamic monitoring for a period of 8 months, highlighting the effect of temperature on automatically identified natural frequencies, the practical feasibility of damage detection methods based on natural frequencies shifts and the key role of permanent dynamic monitoring in the diagnosis of the investigated historic building.
Article
Two examples of monitoring systems of great Venetian Cathedrals, are presented. The first, concerning the Basilica of San Marco, is an example of a long-term monitoring system for a structure that has not undergone any strengthening intervention. The criteria for interpreting this monitoring system data are illustrated. The second example, concerning the Basilica of S. Maria Gloriosa dei Frari, is a clear example of the use of monitoring during the execution of strengthening intervention. This study illustrates the interventions that were carried out on the supporting structures: consolidation of the soil foundation of the bell tower by using the soil-fracturing technique and creation of a structural joint between the bell tower and the Basilica. Through the observational method, this monitoring system was able to check the structural behavior during all the phases of the interventions, thus becoming a precious design tool able to guarantee the safety of the structure and to modify the design solutions during the strengthening intervention, according to the real deformation behavior observed through the monitoring system.
Article
The paper describes the methodology applied to assess the state of preservation of the tallest historic tower in Mantua, the Gabbia Tower, after the Italian earthquakes of May 2012. An extensive experimental programme − including geometric survey, visual inspections, ambient vibration tests, sonic and flat-jack tests − has been planned and carried out to support the future preservation actions of the tower. The paper focuses especially on the outcomes of on-site survey and dynamic tests and highlights the effectiveness of integrating the information obtained from these tests to assess the structural condition and seismic vulnerability of the tower. The adopted experimental methodology, generally suitable as a prompt diagnostic procedure, successfully detected the local vulnerabilities as well as the overall state of preservation of the tower and addressed the subsequent monitoring phase.
Article
Changing environmental conditions, especially temperature, have been observed to be a complicated factor affecting vibration properties, such as frequencies, mode shapes, and damping, of civil structures. This paper reviews technical literature concerning variations in vibration properties of civil structures under changing temperature conditions. Most of these studies focus on variations in frequencies of bridge structures, with some studies on variations in mode shapes and damping and other types of structures. Statistical approaches to correlation between temperature and frequencies are also reviewed. A quantitative analysis shows that variations in material modulus under different temperatures are the major cause of the variations in vibration properties. A comparative study on different structures made of different materials is carried out in laboratory. Two real structures, the 1,377-m main span Tsing Ma Suspension Bridge and the 600-m-tall Guangzhou New Television Tower, are examined. Both laboratory experiments and field testing, regardless of different construction materials used and structural types, verify the quantitative analysis. Variations in frequencies of reinforced concrete structures are much more significant than those of steel structures.
Article
System identification is a fundamental step towards the application of structural health monitoring and damage detection techniques. On this respect, the development of evolved identification strategies is a priority for obtaining reliable and repeatable baseline modal parameters of an undamaged structure to be adopted as references for future structural health assessments. The paper presents the identification of the modal parameters of the Guangzhou New Television Tower, China, using a data-driven stochastic subspace identification (SSI-data) approach complemented with an appropriate automatic mode selection strategy which proved to be successful in previous literature studies. This well-known approach is based on a clustering technique which is adopted to discriminate structural modes from spurious noise ones. The method is applied to the acceleration measurements made available within the task I of the ANCRiSST benchmark problem, which cover 24 hours of continuous monitoring of the structural response under ambient excitation. These records are then subdivided into a convenient number of data sets and the variability of modal parameter estimates with ambient temperature and mean wind velocity are pointed out. Both 10 minutes and 1 hour long records are considered for this purpose. A comparison with finite element model predictions is finally carried out, using the structural matrices provided within the benchmark, in order to check that all the structural modes contained in the considered frequency interval are effectively identified via SSI-data.
Article
Latent variable models can be used to eliminate the environmental or operational effects from the data without measuring the underlying variables and resulting in an increased reliability of damage detection. A method is proposed, which also utilizes the available environmental or operational variables. The method is based on the missing data analysis, in which each feature is estimated in turn using the other features and also the available environmental or operational variables. As damage detection is solely based on the measuremets, training data from the undamaged structure under different environmental or operational conditions are needed. Compared to many other latent variable models, the main advantage of the proposed method is that there are no parameters to be adjusted. The main disadvantage is a higher run time. The method is verified in a numerical study of a vehicle crane with a varying configuration and in an experimental study of a bridge structure under environmental variations. All damage cases were detected using the proposed approach, whereas no indications of damage resulted using the features directly. The importance of the measured environmental or operational variables for damage detection was found to be low, because the features typically consisted all the relevant information.
Article
A fatigue reliability model which integrates the probability distribution of hot spot stress range with a continuous probabilistic formulation of Miner's damage cumulative rule is developed for fatigue life and reliability evaluation of steel bridges with long-term monitoring data. By considering both the nominal stress obtained by measurements and the corresponding stress concentration factor (SCF) as random variables, a probabilistic model of the hot spot stress is formulated with the use of the S-N curve and the Miner's rule, which is then used to evaluate the fatigue life and failure probability with the aid of structural reliability theory. The proposed method is illustrated using the long-term strain monitoring data from the instrumented Tsing Ma Bridge. A standard daily stress spectrum accounting for highway traffic, railway traffic, and typhoon effects is derived by use of the monitoring data. Then global and local finite element models (FEMs) of the bridge are developed for numerically calculating the SCFs at fatigue-susceptible locations, while the stochastic characteristics of SCF for a typical welded T-joint are obtained by full-scale model experiments of a railway beam section of the bridge. A multimodal probability density function (PDF) of the stress range is derived from the monitoring data using the finite mixed Weibull distributions in conjunction with a hybrid parameter estimation algorithm. The failure probability and reliability index versus fatigue life are achieved from the obtained joint PDF of the hot spot stress in terms of the nominal stress and SCF random variables.
Article
When using the analysis of vibration measurements as a tool for health monitoring of bridges, the problem arises of separating abnormal changes from normal changes in the dynamic behaviour. Normal changes are caused by varying environmental conditions such as humidity, wind and most important, temperature. The temperature may have an impact on the boundary conditions and the material properties. Abnormal changes on the other hand are caused by a loss of stiffness somewhere along the bridge. It is clear that the normal changes should not raise an alarm in the monitoring system (i.e. a false positive), whereas the abnormal changes may be critical for the structure's safety. In the frame of the European SIMCES-project, the Z24-Bridge in Switzerland was monitored during almost one year before it was artificially damaged. Black-box models are determined from the healthy-bridge data. These models describe the variations of eigenfrequencies as a function of temperature. New data are compared with the models. If an eigenfrequency exceeds certain confidence intervals of the model, there is probably another cause than the temperature that drives the eigenfrequency variations, for instance damage. Copyright © 2001 John Wiley & Sons, Ltd.
Article
A simplified procedure is described for computation of equivalent potential temperature which remains valid in situations such as in the tropics where a term which is omitted in the derivation of the conventional formula can lead to an error of several degrees absolute. -from Author
Article
Over the past 30 years detecting damage in a structure from changes in global dynamic parameters has received considerable attention from the civil, aerospace and mechanical engineering communities. The basis for this approach to damage detection is that changes in the structure's physical properties (i.e., boundary conditions, stiffness, mass and/or damping) will, in turn, alter the dynamic characteristics (i.e., resonant frequencies, modal damping and mode shapes) of the structure. Changes in properties such as the flexibility or stiffness matrices derived from measured modal properties and changes in mode shape curvature have shown promise for locating structural damage. However, to date there has not been a study reported in the technical literature that directly compares these various methods. The experimental results reported in this paper and the results of a numerical study reported in an accompanying paper attempt to fill this void in the study of damage detection methods. Five methods for damage assessment that have been reported in the technical literature are summarized and compared using experimental modal data from an undamaged and damaged bridge. For the most severe damage case investigated, all methods can accurately locate the damage. The methods show varying levels of success when applied to less severe damage cases. This paper concludes by summarizing some areas of the damage identification process that require further study.
Article
Numerous investigations have indicated that structural modal parameters are significantly impacted by varying environmental and operational conditions. This phenomenon will cause confusion when conducting modal-based damage detection and model updating. This paper investigates the dependency of modal frequencies, modal shapes and the associated damping ratios on temperature and wind velocity. The nonlinear principal component analysis (NLPCA) is first employed as a signal pre-processing tool to distinguish temperature and wind effects on structural modal parameters from other environmental factors. The pre-processed dataset by NLPCA implies the relationship between modal parameters and temperature as well as wind velocity. Consequently, the artificial neural network (ANN) technique is employed to model the relationship between the pre-processed modal parameters and environmental factors. Numerical results indicate that pre-processed modal parameters by NLPCA can retain the most features of original signals. Furthermore, the pre-processed modal frequency and damping ratios are dramatically affected by temperature and wind velocity. The ANN regression models have good capacities for mapping relationship of environmental factors and modal frequency, damping ratios. However, environmental effects on the entire modal shapes are insignificant. Copyright © 2009 John Wiley & Sons, Ltd.
Article
In vibration-based condition assessment exercises, it is necessary to discriminate the variation of structural properties due to environmental changes from those caused by structural damages. Some efforts have been made to correlate the structural vibration characteristics and the air temperature or temperatures at the structural surface. As the temperature of an entire structure is generally non-uniformly distributed, using the air temperature or surface temperatures alone may not sufficiently capture the relation between the structural responses and temperatures. The present paper aims to investigate the variation of the structural vibration characteristics versus the non-uniform temperature field of the structure. Thermodynamic models are employed to estimate the temperature at different components of the structure at different times. As the material mechanical properties are temperature dependent, the structure can be regarded as a composite structure consisting of elements with different Young’s moduli. Consequently, the natural frequencies of the structure can be calculated with the finite element method. The procedures are repeated for different times and thus variation of the frequencies with respect to time is obtained. A simply supported RC slab was constructed and used as a proof-of-concept example. The temperatures at different points of the slab were recorded continuously in one day, together with a series of forced modal testing to extract its modal properties. On the other hand, a finite element model was established to conduct a transient thermal analysis and estimate the temperature distribution of the slab, which shows a good agreement with the measurement counterpart. The temperature data at all components and thermal properties of the material were then inputted to the model to calculate the frequencies, which also matched the measured frequencies very well. Moreover, a good linear correlation between the natural frequencies measured and the structural temperatures other than the air temperature or surface temperatures is observed. The present study provides a new approach to quantifying the environmental effect on the structural vibration characteristics.
Article
Interest in the ability to monitor a structure and detect damage at the earliest possible stage is pervasive throughout the civil, mechanical and aerospace engineering communities. Significant work has been done in the formulation of vibration-bas ed damage detection algorithms, but unfortunately, investigations studying the variability of dynamic properties caused by changing environmental and operational conditions have been lacking. A thorough understanding of this variability is necessary so that changes in vibration response resulting from damage can be discriminated from changes resulting from such variability. In this paper the variability in modal properties of the Alamosa Canyon Bridge in southern New Mexico will be discussed.
Article
This paper focuses on developing an online structural condition assessment technique using long-term monitoring data measured by a structural health monitoring system. The seasonal correlations of frequency-temperature and beam-end displacement-temperature for the Runyang Suspension Bridge are performed, first. Then, a statistical modeling technique using a six-order polynomial is further applied to formulate the correlations of frequency-temperature and displacement-temperature, from which abnormal changes of measured frequencies and displacements are detected using the mean value control chart. Analysis results show that modal frequencies of higher vibration modes and displacements have remarkable seasonal correlations with the environmental temperature and the proposed method exhibits a good capability for detecting the micro damage-induced changes of modal frequencies and displacements. The results demonstrate that the proposed method can effectively eliminate temperature complications from frequency and displacement time series and is well suited for online condition monitoring of long-span suspension bridges. Keywordsstructural health monitoring-modal frequency-beam-end displacement-temperature-seasonal correlation-suspension bridge
Article
Changes in environmental conditions such as temperature and humidity affect structural vibration properties. Other researchers have reported that modal frequencies varied significantly in a single day due to temperature change. Therefore, it is necessary to discriminate the variation of modal properties due to environmental change from those caused by structural damage, and quantify the environmental effect in vibration-based structural health monitoring and damage identification. Environmental conditions affect structural vibration properties in a complicated manner; this paper only investigates the variation of frequencies, mode shapes and damping with respect to temperature and humidity changes. A reinforced concrete slab, which was constructed and placed outside the laboratory, has been periodically vibration tested for nearly two years. This paper reports results obtained over that time for the first four modes. It is found that the frequencies have a strong negative correlation with temperature and humidity, damping ratios have a positive correlation, but no clear correlation of mode shapes with temperature and humidity change can be observed. Linear regression models between modal properties and environmental factors are built. A quantification analysis shows that variation of the elastic modulus of the material is the primary cause of the variation of modal properties.
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.
Article
The establishment of a baseline is essential for long-term structural health monitoring and performance evaluation. Usually, field testing data and finite element (FE) model are two critical tools used to develop the baseline. In this paper, the establishment of the baseline field database for a curved post-tensioned concrete bridge with expansion bearings is first introduced to include the effect of varying temperature conditions on the field testing data. This database uses data collected from a full year and is based on an undamaged status. The development of a baseline FE model for the bridge is then discussed. Model updating for the FE model are detailed in this paper which includes calibration of material properties, utilization of spring bearing elements, and replacement of Mindlin plate elements (MP4) on box–girder by recently developed cracked Mindlin plate elements (MP4C) to represent the bridge service conditions. A good agreement in modal results has been observed between the baseline FE model and the baseline field data. The proposed structural health baseline can be used for near real-time damage detection, development of monitoring techniques, and condition assessment. Finally, as an application of the baseline, this FE model is used for an earthquake simulation with a selected ground motion on the bridge. The seismic analysis demonstrates the beneficial effect of the guided expansion bearings on the bridge deck in the longitudinal direction.
Article
The significance of implementing long-term structural health monitoring systems for large-scale bridges, in order to secure structural and operational safety and issue early warnings on damage or deterioration prior to costly repair or even catastrophic collapse, has been recognized by bridge administrative authorities. Developing a long-term monitoring system for a large-scale bridge—one that is really able to provide information for evaluating structural integrity, durability and reliability throughout the bridge life cycle and ensuring optimal maintenance planning and safe bridge operation—poses technological challenges at different levels, from the selection of proper sensors to the design of a structural health evaluation system. This paper explores recent technology developments in the field of structural health monitoring and their application to large-scale bridge projects. The need for technological fusion from different disciplines, and for a structural health evaluation paradigm that is really able to help prioritize bridge rehabilitation, maintenance and emergency repair, is highlighted.
Article
A damage detection method is proposed for structural health monitoring under varying environmental and operational conditions. The method is based on principal component analysis (PCA) applied to vibration features identified during the monitoring of the structure. The advantage of the method is that it does not require to measure environmental parameters because they are taken into account as embedded variables. The number of principal components of the vibration features is implicitly assumed to correspond to the number of independent environmental factors. Since the environmental effects may be effectively eliminated by the proposed procedure, the residual error of the PCA prediction model remains small if the structure is healthy, and it increases significantly when structural damage occurs. Novelty analysis on the residual errors provides a statistical indication of damage. In the present paper, the environmental conditions are assumed to have a linear (or weakly non-linear) effect on the vibration features, and the PCA-based damage detection method is illustrated using computer-simulated and laboratory testing data. The extension of the proposed method to non-linear cases is addressed in a companion paper where the efficiency of the method is verified using data obtained from a 1-year in situ monitoring of a bridge.
Article
The “Infante D. Henrique” bridge is a concrete arch bridge, with a span of 280 m that crosses the Douro River, linking the cities of Porto and Gaia located in the North of Portugal. This structure is being monitored by a recently installed dynamic monitoring system that comprises 12 acceleration channels. This paper describes the bridge structure, its dynamic parameters identified with a previously developed ambient vibration test, the installed monitoring equipment and the software that continuously processes the data received from the bridge through an Internet connection. Special emphasis is given to the algorithms that have been developed and implemented to perform the online automatic identification of the structure modal parameters from its measured responses during normal operation. The proposed methodology uses the covariance driven stochastic subspace identification method (SSI-COV), which is then complemented by a new algorithm developed for the automatic analysis of stabilization diagrams. This new tool, based on a hierarchical clustering algorithm, proved to be very efficient on the identification of the bridge first 12 modes. The results achieved during 2 months of observation, which involved the analysis of more than 2500 datasets, are presented in detail. It is demonstrated that with the combination of high-quality equipment and powerful identification algorithms, it is possible to estimate, in an automatic manner, accurate modal parameters for several modes. These can then be used as inputs for damage detection algorithms.