System Identification of Constructed Facilities: Challenges and Opportunities Across Hazards

The motivation, success and prevalence of full-scale monitoring of constructed buildings vary considerably across the hazard of concern (earthquakes, strong winds, etc.), due in part to various fiscal and life safety motivators. Yet while the challenges of successful deployment and operation of large-scale monitoring initiatives are significant, they are perhaps dwarfed by the challenges of data management, interrogation and ultimately system identification. Practical constraints on everything from sensor density to the availability of measured input has driven the development of a wide array of system identification and damage detection techniques, which in many cases become hazard-specific. In this study, the authors share their experiences in fullscale monitoring of buildings across hazards and the associated challenges of system identification. The study will conclude with a brief agenda for next generation research in the area of system identification of constructed facilities

Long term monitoring and field testing of an innovative multi-storey timber building

Peer reviewedPostprin

Health monitoring of web plastifying dampers subjected to cyclic loading through vibration tests

This article investigates experimentally the application of health monitoring techniques to assess the damage on a particular kind of hysteretic (metallic) damper called web plastifying dampers, which are subjected to cyclic loading. In general terms, hysteretic dampers are increasingly used as passive control systems in advanced earthquake-resistant structures. Nonparametric statistical processing of the signals obtained from simple vibration tests of the web plastifying damper is used here to propose an area index damage. This area index damage is compared with an alternative energy-based index of damage proposed in past research that is based on the decomposition of the load?displacement curve experienced by the damper. Index of damage has been proven to accurately predict the level of damage and the proximity to failure of web plastifying damper, but obtaining the load?displacement curve for its direct calculation requires the use of costly instrumentation. For this reason, the aim of this study is to estimate index of damage indirectly from simple vibration tests, calling for much simpler and cheaper instrumentation, through an auxiliary index called area index damage. Web plastifying damper is a particular type of hysteretic damper that uses the out-of-plane plastic deformation of the web of I-section steel segments as a source of energy dissipation. Four I-section steel segments with similar geometry were subjected to the same pattern of cyclic loading, and the damage was evaluated with the index of damage and area index damage indexes at several stages of the loading process. A good correlation was found between area index damage and index of damage. Based on this correlation, simple formulae are proposed to estimate index of damage from the area index damage

Assessment of dynamic and long-term performance of an innovative multi-story timber building via structural monitoring and dynamic testing

Peer reviewedPostprin

Studies on nonlinear mechanical wave behavior to characterize cement based materials and its durability

[EN] The test for determining the resonance frequencies has traditionally been used to investigate the mechanical integrity of concrete cores, to assess the conformity of concrete constituents in different accelerated durability tests, and to ascertain constitutive properties such as the elastic modulus and the damping factor. This nondestructive technique has been quite appealed for evaluation of mechanical properties in all kinds of durability tests. The damage evolution is commonly assessed from the reduction of dynamic modulus which is produced as a result of any cracking process. However, the mechanical behavior of concrete is intrinsically nonlinear and hysteretic. As a result of a hysteretic stress-strain behavior, the elastic modulus is a function of the strain. In dynamic tests, the nonlinearity of the material is manifested by a decrease of the resonance frequencies, which is inversely proportional to the excitation amplitude. This phenomenon is commonly referred as fast dynamic effect. Once the dynamic excitation ceases, the material undergoes a relaxation process whereby the elastic modulus is restored to that at rest. This phenomenon is termed as slow dynamics. These phenomena (fast and slow dynamics) find their origin in the internal friction of the material. Therefore, in cement-based materials, the presence of microcracks and interfaces between its constituents plays an important role in the material nonlinearity. In the context of the assessment of concrete durability, the damage evolution is based on the increase of hysteresis, as a result of any cracking process. In this thesis three different nondestructive techniques are investigated, which use impacts for exciting the resonant frequencies. The first technique consists in determining the resonance frequencies over a range of impact forces. The technique is termed Nonlinear Impact Resonant Acoustic Spectroscopy (NIRAS). It consists in ascertaining the downward resonant frequency shift that the material undergoes upon increasing excitation amplitude. The second technique consists in investigating the nonlinear behavior by analyzing the signal corresponding to a single impact. This is, to determine the instantaneous frequency, amplitude and attenuation variations corresponding to a single impact event. This technique is termed as Nonlinear Resonant Acoustic Single Impact Spectroscopy (NSIRAS). Two techniques are proposed to extract the nonlinear behavior by analyzing the instantaneous frequency variations and attenuation over the signal ring down. The first technique consists in discretizing the frequency variation with time through a Short-Time Fourier Transform (STFT) based analysis. The second technique consists of a least-squares fit of the vibration signals to a model that considers the frequency and attenuation variations over time. The third technique used in this thesis can be used for on-site evaluation of structures. The technique is based on the Dynamic Acousto- Elastic Test (DAET). The variations of elastic modulus as derived through NIRAS and NSIRAS techniques provide an average behavior and do not allow derivation of the elastic modulus variations over one vibration cycle. Currently, DAET technique is the only one capable to investigate the entire range of nonlinear phenomena in the material. Moreover, unlike other DAET approaches, this study uses a continuous wave source as probe. The use of a continuous wave allows investigation of the relative variations of the elastic modulus, as produced by an impact. Moreover, the experimental configuration allows one-sided inspection.[ES] El ensayo de determinación de las frecuencias de resonancia ha sido tradicionalmente empleado para determinar la integridad mecánica de testigos de hormigón, en la evaluación de la conformidad de mezclas de hormigón en diversos ensayos de durabilidad, y en la terminación de propiedades constitutivas como son el módulo elástico y el factor de amortiguamiento. Esta técnica no destructiva ha sido ampliamente apelada para la evaluación de las propiedades mecánicas en todo tipo de ensayos de durabilidad. La evolución del daño es comúnmente evaluada a partir de la reducción del módulo dinámico, producido como resultado de cualquier proceso de fisuración. Sin embargo, el comportamiento mecánico del hormigón es intrínsecamente no lineal y presenta histéresis. Como resultado de un comportamiento tensión-deformación con histéresis, el módulo elástico depende de la deformación. En ensayos dinámicos, la no linealidad del material se manifiesta por una disminución de las frecuencias de resonancia, la cual es inversamente proporcional a la amplitud de excitación. Este fenómeno es normalmente denominado como dinámica rápida. Una vez la excitación cesa, el material experimenta un proceso de relajación por el cual, el módulo elástico es restaurado a aquel en situación de reposo. Este fenómeno es denominado como dinámica lenta. Estos fenómenos ¿dinámicas rápida y lenta¿ encuentran su origen en la fricción interna del material. Por tanto, en materiales basados en cemento, la presencia de microfisuras y las interfaces entre sus constituyentes juegan un rol importante en la no linealidad mecánica del material. En el contexto de evaluación de la durabilidad del hormigón, la evolución del daño está basada en el incremento de histéresis, como resultado de cualquier proceso de fisuración. En esta tesis se investigan tres técnicas diferentes las cuales utilizan el impacto como medio de excitación de las frecuencias de resonancia. La primera técnica consiste en determinar las frecuencias de resonancia a diferentes energías de impacto. La técnica es denominada en inglés: Nonlinear Impact Resonant Acoustic Spectroscopy (NIRAS). Ésta consiste en relacionar el detrimento que el material experimenta en sus frecuencias de resonancia, con el aumento de la amplitud de la excitación. La segunda técnica consiste en investigar el comportamiento no lineal mediante el análisis de la señal correspondiente a un solo impacto. Ésta consiste en determinar las propiedades instantáneas de frecuencia, atenuación y amplitud. Esta técnica se denomina, en inglés, Nonlinear Single Impact Resonant Acoustic Spectroscopy (NSIRAS). Se proponen dos técnicas de extracción del comportamiento no lineal mediante el análisis de las variaciones instantáneas de frecuencia y atenuación. La primera técnica consiste en la discretización de la variación de la frecuencia con el tiempo, mediante un análisis basado en Short-Time Fourier Transform (STFT). La segunda técnica consiste en un ajuste por mínimos cuadrados de las señales de vibración a un modelo que considera las variaciones de frecuencia y atenuación con el tiempo. La tercera técnica empleada en esta tesis puede ser empleada para la evaluación de estructuras in situ. La técnica se trata de un ensayo acusto-elástico en régimen dinámico. En inglés Dynamic Acousto-Elastic Test (DAET). Las variaciones del módulo elástico obtenidas mediante los métodos NIRAS y NSIRAS proporcionan un comportamiento promedio y no permiten derivar las variaciones del módulo elástico en un solo ciclo de vibración. Actualmente, la técnica DAET es la única que permite investigar todo el rango de fenómenos no lineales en el material. Por otra parte, a diferencia de otras técnicas DAET, en este estudio se emplea como contraste una onda continua. El uso de una onda continua permite investigar las variaciones relativas del módulo elástico, para una señal transito[CA] L'assaig de determinació de les freqüències de ressonància ha sigut tradicionalment empleat per a determinar la integritat mecànica de testimonis de formigó, en l'avaluació de la conformitat de mescles de formigó en diversos assajos de durabilitat, i en la terminació de propietats constitutives com són el mòdul elàstic i el factor d'amortiment. Esta tècnica no destructiva ha sigut àmpliament apel·lada per a l'avaluació de les propietats mecàniques en tot tipus d'assajos de durabilitat. L'evolució del dany és comunament avaluada a partir de la reducció del mòdul dinàmic, produït com resultat de qualsevol procés de fisuración. No obstant això, el comportament mecànic del formigó és intrínsecament no lineal i presenta histèresi. Com resultat d'un comportament tensió-deformació amb histèresi, el mòdul elàstic depén de la deformació. En assajos dinàmics, la no linealitat del material es manifesta per una disminució de les freqüències de ressonància, la qual és inversament proporcional a l'amplitud d'excitació. Este fenomen és normalment denominat com a dinàmica ràpida. Una vegada l'excitació cessa, el material experimenta un procés de relaxació pel qual, el mòdul elàstic és restaurat a aquell en situació de repòs. Este fenomen és denominat com a dinàmica lenta. Estos fenòmens --dinámicas ràpida i lenta troben el seu origen en la fricció interna del material. Per tant, en materials basats en ciment, la presència de microfissures i les interfícies entre els seus constituents juguen un rol important en la no linealitat mecànica del material. En el context d'avaluació de la durabilitat del formigó, l'evolució del dany està basada en l'increment d'histèresi, com resultat de qualsevol procés de fisuración. En esta tesi s'investiguen tres tècniques diferents les quals utilitzen l'impacte com a mitjà d'excitació de les freqüències de ressonància. La primera tècnica consistix a determinar les freqüències de ressonància a diferents energies d'impacte. La tècnica és denominada en anglés: Nonlinear Impact Resonant Acoustic Spectroscopy (NIRAS). Esta consistix a relacionar el detriment que el material experimenta en les seues freqüències de ressonància, amb l'augment de l'amplitud de l'excitació. La segona tècnica consistix a investigar el comportament no lineal per mitjà de l'anàlisi del senyal corresponent a un sol impacte. Esta consistix a determinar les propietats instantànies de freqüència, atenuació i amplitud. Esta tècnica es denomina, en anglés, Nonlinear Single Impact Resonant Acoustic Spectroscopy (NSIRAS). Es proposen dos tècniques d'extracció del comportament no lineal per mitjà de l'anàlisi de les variacions instantànies de freqüència i atenuació. La primera tècnica consistix en la discretización de la variació de la freqüència amb el temps, per mitjà d'una anàlisi basat en Short-Time Fourier Transform (STFT). La segona tècnica consistix en un ajust per mínims quadrats dels senyals de vibració a un model que considera les variacions de freqüència i atenuació amb el temps. La tercera tècnica empleada en esta tesi pot ser empleada per a l'avaluació d'estructures in situ. La tècnica es tracta d'un assaig acusto-elástico en règim dinàmic. En anglés Dynamic Acousto-Elastic Test (DAET). Les variacions del mòdul elàstic obtingudes per mitjà dels mètodes NIRAS i NSIRAS proporcionen un comportament mitjà i no permeten derivar les variacions del mòdul elàstic en un sol cicle de vibració. Actualment, la tècnica DAET és l'única que permet investigar tot el rang de fenòmens no lineals en el material. D'altra banda, a diferència d'altres tècniques DAET, en este estudi s'empra com contrast una ona contínua. L'ús d'una ona contínua permet investigar les variacions relatives del mòdul elàstic, per a un senyal transitori. A més, permet la inspecció d'elements per mitjà de l'accés per una sola cara.Eiras Fernández, JN. (2016). Studies on nonlinear mechanical wave behavior to characterize cement based materials and its durability [Tesis doctoral]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/71439TESISPremios Extraordinarios de tesis doctorale

Damage detection of rubber-bearing isolated building based on AEKF approach

In order to detect the damages in rubber-bearing isolated structures, a rubber-bearing isolated building model was established and tested on shake table experimentally in the laboratory. Different earthquakes were used to drive the shake table and the stiffness element device (SED) was adopted herein to reduce the stiffness of the upper story of the model abruptly to simulate structural damages during the test. The adaptive extended Kalman filter (AEKF) approach is proposed to identify the parameters and track the parametric variation of rubber-bearing isolated structure online and to identify the displacements of every story using the measured acceleration responses. The identification results of the experiments demonstrate that the AEKF approach is capable of identifying the parameters of rubber-bearing isolated structure accurately and tracking the parametric variations of the structure effectively, leading to the detection of structural damages, including the damage locations and severity. And the predicted displacements also match well with the experimental data, indicating the effectiveness and accuracy of the proposed AEKF approach in detecting the damages in rubber-bearing isolated structures with practical application value

Monitoring and Self-diagnosis of Civil Engineering Structures: Classical and Innovative Applications

Eventi estremi come esplosioni o terremoti possono avere un profondo impatto nella sicurezza degli edifici. Le zone sismiche devono convivere con questi tragici eventi, per questo monitorare in maniera continua le condizioni di salute di una struttura è necessario e auspicabile in molti casi. Il monitoraggio strutturale (Structural Health Monitoring – SHM) rappresenta un potente strumento per la valutazione del comportamento dinamico della struttura monitorata. Fino a pochi anni fa queste tecniche erano impiegate prevalentemente in ambito meccanico, aeronautico e nell’ingegneria aerospaziale. Al giorno d’oggi, la riduzione dei costi della strumentazione, sistemi di acquisizione dati di nuova generazione e l’incremento continuo dell’efficienta nelle analisi numeriche hanno reso possibile l’applicazione di queste tecniche anche a strutture civili ordinarie. Le tecniche di monitoraggio strutturale vengono applicate non solo in grandi infrastrutture come ponti, dighe o grattacieli, ma anche in strutture storiche o edifici residenziali. In questo contesto questa tesi tenta di esaminare differenti aspetti del monitoraggio strutturale, in particolar modo riferite a edifici ordinari. Attraverso tecniche Output-Only (Operational Modal Analysis – OMA) sono state monitorate diverse strutture civili con reti di sensori cablate, al fine di ottenere il comportamento dinamico strutturale nelle reali condizioni opertive. Particolare attenzione è stata focalizzata in un altra importante tematica dell’ingegneria strutturale: il danneggiamento strutturale. Attraverso un approccio numerico viene presentato un nuovo metodo per la localizzazione e quantificazione del danno a seguito di un evento sismico. In alternativa alla classica rete cablata, è stato sviluppato un sistema di acquisizione con sensori wireless (Wireless Sensor Network – WSN). I principali risultati ottenuti con questa applicazione vengono riportati nella presente tesi, unitamente al design dei sensori low-cost. Con l’ausilio della sensoristica sviluppata è stato monitorato un edificio storico in muratura, mostrando i risultati positivi ottenuti a seguito della campagna di acquisizione di rumore ambientale (Ambient Vibration Survey -AVS).Extreme events like explosions and earthquakes may have a deep impact on building safety. Seismic regions must live with these tragic events, so that continuous monitoring of structure health conditions is necessary in many cases. Structural Health Monitoring (SHM) represents a powerful tool for the evaluation of dynamic behavior of monitored structures. Until a few years ago these techniques were widely employed especially in mechanical, aeronautical and aerospace engineering. Nowadays, the reduction of equipment costs, the new generation of data acquisition systems, together with the continuous improvement of computational analysis have made it possible to apply SHM also to civil structures without strategic importance. SHM has moved from large infrastructures like bridges, dams and skyscrapers to historical heritage and residential buildings. In this background, the present work tries to examine different aspects of SHM applications, especially referred to ordinary buildings. Using Operational Modal Analysis (OMA) techniques, several civil structures have been monitored through a wired network sensor, in order to obtain the dynamic behavior in operating conditions. The relevant data collection provides a useful tool for calibrating the accuracy and sensitivity of similar SHM case studies. Specific attention is focused in another important issue in civil and in mechanical engineering: detection of structural damages. Through a numerical approach, a new method for damage localization and quantification is proposed. Besides the traditional wired acquisition system a Wireless Sensor Network (WSN) has been developed. The issues related to the usage of low-cost sensors and new generation data acquisition tools for non-destructive structural testing are discussed. Using the WSN an historical masonry building has been monitored, showing the positive results obtained following the Ambient Vibration Survey (AVS)

An intelligent parameter varying (IPV) approach for non-linear system identification of base excited structures

Health monitoring and damage detection strategies for base-excited structures typically rely on accurate models of the system dynamics. Restoring forces in these structures can exhibit highly non-linear characteristics, thus accurate non-linear system identification is critical. Parametric system identification approaches are commonly used, but require a priori knowledge of restoring force characteristics. Non-parametric approaches do not require this a priori information, but they typically lack direct associations between the model and the system dynamics, providing limited utility for health monitoring and damage detection. In this paper a novel system identification approach, the intelligent parameter varying (IPV) method, is used to identify constitutive non-linearities in structures subject to seismic excitations. IPV overcomes the limitations of traditional parametric and non-parametric approaches, while preserving the unique benefits of each. It uses embedded radial basis function networks to estimate the constitutive characteristics of inelastic and hysteretic restoring forces in a multi-degree-of-freedom structure. Simulation results are compared to those of a traditional parametric approach, the prediction error method. These results demonstrate the effectiveness of IPV in identifying highly non-linear restoring forces, without a priori information, while preserving a direct association with the structural dynamics

Experimental study on parameter identification of rubber-bearings based on quadratic sum-squares error

In this paper, the QSSE method has been used for experimental study on parameter identification of rubber-bearings, the experimental model of rubber-bearings has been built and the widely used Bouc-Wen model has been investigated to represent the hysteretic behavior of rubber-bearing isolators. Further, experimental tests using a particular type of rubber-bearing (GZN110) have been conducted to measure base accelerations and model accelerations. Based on experimental vibration data measured from sensors, the QSSE method is used to identify the model parameters and displacements. Experimental results demonstrate that the estimated parameters are identical, and the identified displacements match the experimental ones well based on different excitation scenarios, i.e., different kinds of earthquakes with different peak ground accelerations. The influence on the estimated parameters based on the changes of initial parameters is little. It demonstrates that the Bouc-Wen model is capable of describing the nonlinear behavior of rubber-bearings. Compared with the EKF method, the QSSE method calculates faster, which demonstrates that the QSSE approach has better robustness and calculation efficiency and is quite effective and accurate for parameter identification of nonlinear hysteretic rubber-bearings