Papers by oscar curadelli
Structural Health Monitoring (SHM) is an increasingly important field in civil engineering, as it... more Structural Health Monitoring (SHM) is an increasingly important field in civil engineering, as it plays a crucial role in detecting changes in the condition of structures and identifying potential damage. To achieve this, SHM strategies often employ Artificial Intelligence (AI) techniques, which involve analyzing raw dynamic data obtained from structures to perform classifications or extract relevant features. Among the various AI algorithms used in SHM, autoencoders and convolutional neural networks (CNNs) have emerged as promising solutions, and this article focuses on discussing their application.
Expert Systems With Applications, Feb 1, 2017
Output-only system identification under non-white-noise excitation is addressed.The classical app... more Output-only system identification under non-white-noise excitation is addressed.The classical approach consists in using long records.The white-noise excitation assumption is trivially validated during free-vibration.An algorithm is developed to automatically find free-vibration record segments.The proposed approach requires short records, leading to hardware simplifications. Output-only system identification is a very attractive technique for its implementation simplicity. However, it requires long records to validate the white-noise assumption of the excitation, mainly under transient forced vibration. Alternatively, free-vibration record segments can be selected before the identification process. This improves the accuracy, even using less data, but it requires human intervention or input recording. In the present paper, an approach is proposed for accurate system identification from short output-only records of vibration induced by transient excitation, without human intervention. The approach is based on a novel heuristic search algorithm to find free-vibration record segments, which is fully automatic and it handles the possibility of free-vibration absence. Tests with real-life data from Structural Health Monitoring (SHM) of a bridge showed that the free-vibration finding improves the accuracy of the modal parameter estimates up to ten times, as compared to using record segments starting at the response peak. The proposed approach drastically reduces the need to transmit large amounts of data, which impacts on hardware requirements of SHM implementations.
Mecánica Computacional, Nov 28, 2018
Resumen. Las formas modales obtenidas experimentalmente contienen importante información acerca d... more Resumen. Las formas modales obtenidas experimentalmente contienen importante información acerca de la salud estructural. En particular, la curvatura modal estimada numéricamente a partir de dichas formas modales ha sido útil para detectar y localizar daño muy concentrado; pero no para cuantificarlo físicamente, porque en la práctica el error numérico es grande y dependiente del tamaño del paso. En vista de esto, el presente trabajo propone una reinterpretación de las fórmulas clásicas de diferencias finitas, demostrando que son también aproximaciones de los valores medios de las derivadas a lo largo de un intervalo asociado a la disposición de los puntos de muestreo. Esta reinterpretación permite determinar una relación explícita entre la curvatura modal, estimada con una disposición de puntos de muestreo, y la rigidez flexional del tramo asociado a dicha disposición. A partir de este dato físicamente representativo de un tramo, podrían hacerse estimaciones más certeras del grado de daño real, con cierta independencia del paso. La metodología propuesta se puso a prueba mediante el análisis modal de un modelo de elementos finitos de una viga simplemente apoyada con distintas reducciones de sección.
International Journal of Civil Engineering, Apr 5, 2017
To improve the structural seismic response of liquid storage tanks, in the last 50 years, many re... more To improve the structural seismic response of liquid storage tanks, in the last 50 years, many researchers have developed different mathematical models, ranging from those based on discrete elements such as simplified two-mass models to those involving fluid–structure interactions by complex formulations. To provide a broad overview on the scope and accuracy of different numerical linear models, in this paper, a comparative study based on the dynamic response assessment of cylindrical ground-supported containers under seismic excitation is conducted. The dynamic response in terms of liquid sloshing height, base shear force and overturning moment is analysed by means of: (a) a simplified mechanical model in which the behaviour of the liquid is represented by a discrete mass-spring system; (b) a complex model based on a Lagrangian fluid finite element approximation and (c) an experimental scaled model whose measured response is considered as benchmark. To obtain robust estimators of the structural response, three different types of cylindrical tanks, including broad and slender tanks, subjected to real ground acceleration time-histories are studied. The results indicate that the finite element model gives good approximation for all response parameters and the simplified mechanical model underestimate the sloshing height and overestimate base shear force and overturning moment.
Journal of Sound and Vibration, Jul 1, 2017
In the last two decades, great efforts were carried out to reduce the seismic demand on structure... more In the last two decades, great efforts were carried out to reduce the seismic demand on structures through the concept of energy dissipation instead of increasing the stiffness and strength. Several devices based on different energy dissipation principles have been developed and implemented worldwide, however, most of the dissipation devices are usually installed using diagonal braces, which entail certain drawbacks on apertures for circulation, lighting or ventilation and architectural or functional requirements often preclude this type of installations. In this work, a conceptual development of a novel energy dissipation device, called Multiple Friction Damper (MFD), is proposed and examined. To verify its characteristics and performance, the MFD was implemented on a single storey steel frame experimental model and tested under different conditions of normal force and real time acceleration records. Experimental results demonstrated that the new MFD constitutes an effective and reliable alternative to control the structural response in terms of displacement and acceleration. A mathematical formulation based on the Wen's model reflecting the nonlinear behaviour of the device is also presented.
Journal of Loss Prevention in The Process Industries, Sep 1, 2018
It is known that, earthquakes have caused severe damages to a large number of industrial faciliti... more It is known that, earthquakes have caused severe damages to a large number of industrial facilities, mainly storage tanks with extremely serious economic and environmental implications. Thus, it is extremely importance to use techniques for reducing the seismic vulnerability of such structures. Seismic base isolation as seismic protection technology is already known and its development continues to grow. The present paper focuses on the seismic performance of broad and slender atmospheric storage steel tanks base isolated by Sliding Concave Bearings (SCB). The performance study carried out through shaking table tests on a vertical cylindrical steel tank model allowed to determine quantitatively the efficiency of the SCB by analyzing two structural parameters: (a) sloshing height and (b) base shear force. Six real ground motions with different characteristics were considered. Results show the effectiveness of SCB in reducing the base shear force values for all studied cases without significantly affecting the sloshing displacements when compared with fixed-base support.
Procedia Engineering, 2017
For controlling vibrations, a Semi-Active Friction Tendon (SAFT), which consists of a semi-active... more For controlling vibrations, a Semi-Active Friction Tendon (SAFT), which consists of a semi-active friction damper and an auxiliary spring that are linked to the structure by a cable, is studied experimentally, numerically and analytically. Two semiactive control laws are implemented, one is based on velocity feedback (denoted as SQDCL) and the other is based on force feedback (denoted as SPCL); the passive control case is also studied for comparison. Based on the structural displacement reduction and the hysteretic behavior assessment, it is clearly demonstrated that (for SAFTs with a given pre-tension force): (1) the effectiveness of the optimized passive-control case can always be improved by using semi-active control with any of the two control laws; and (2) the SPCL is more effective for large displacements, while the SQDCL is more advantageous for very small displacements. Moreover, closed-form expressions for the dissipated energy are presented for the three cases under consideration, which can be used in preliminary design of SAFTs to decide between passive and semi-active control and to choose the more suitable control law.
Structural control & health monitoring, Aug 22, 2019
Semiactive control systems are based on formerly passive mechanical devices whose characteristics... more Semiactive control systems are based on formerly passive mechanical devices whose characteristics are adjusted in real time by active means. They can be classified into variable-damping dampers, variable-stiffness springs, and variable-inertance inerters. Similarly to the case of "variable-stiffness," two possibilities are devised for inerters: "independently-variable inertance," where inertance can increase or decrease continuously at any instant of time, and "resettable-inertance," where it can increase only at instants where relative velocity is zero. By duality with resettable-stiffness springs, a resettable-inertance inerter (RII) is composed of an inerter that can suddenly be disconnected from the vibrating system and blocked in order to eliminate kinetic energy. Studies on "independently-variable inertance" have been carried out recently, but there are still no studies on "resettable inertance." This paper presents an analytical numerical study on RII, for an energy-based control law, through the mathematical model of a mechanical implementation. By simulation of a numerical example that considers a SDOF system with three different devices, the performance is demonstrated for energy absorption and vibration reduction. Moreover, closed-form expressions for the equivalent-linear inertance, stiffness, and damping are found for the resettable devices and validated through the numerical example. Main conclusion is that RII adds equivalent damping without dynamically stiffening the structure. Besides, the absorbed energy can be dissipated and/or harvested in time intervals in which the RII is uncoupled from the structure.
Smart Structures and Systems, Oct 1, 2019
Structure and Infrastructure Engineering, May 11, 2023
Journal of Sound and Vibration, Feb 1, 2014
Lyapunov-based control is an attractive strategy for semi-active vibration control as it has a ma... more Lyapunov-based control is an attractive strategy for semi-active vibration control as it has a mathematical basis ensuring stability in the sense of Lyapunov and great flexibility in the design. Unfortunately, that flexibility complicates the controller tuning since it involves the construction of a weighting matrix, which is usually done by trial-and-error. In this work, a straightforward (closed form) method to construct such a matrix is proposed. The proposed method is based on penalizing vibrational modes according to their contributions to the response in the uncontrolled case. For this purpose, a new concept of Generalized Modal Contribution Factor is developed. This takes into account the following: spatial distribution of the excitation, knowledge of the frequency content of the excitation, and control objective. The capability of the proposed tuning method is demonstrated through a numerical example.
Engineering Structures, Mar 1, 2018
Vibration control systems are usually classified into: passive, active and semi-active. Semi-acti... more Vibration control systems are usually classified into: passive, active and semi-active. Semi-active control systems are based on formerly passive mechanical devices, such as springs and dampers, whose characteristics are adjusted in real-time by active means. The attractiveness of semi-active control systems mainly relies on their assumed "inherent stability", which makes them almost as reliable and fault-tolerant as passive control systems. The present paper shows that these assumptions are only partially true, by applying passivity formalism and bounded-input bounded-output stability definitions. Based on this study, semi-active control devices are rationally classified into three classes with two subclasses each: (1.1) non-negative variable-damping dampers, (1.2) possibly-negative variable-damping dampers, (2.1) independently-variable-stiffness springs, (2.2) resettable-stiffness springs, (3.1) independently-variable-inertance inerters, and (3.2) resettable-inertance inerters. It is found that a control system using any of the semi-active control devices of type (1.2), (2.1) or (3.1) is not inherently stable, as it is assumed in some previous papers; because those devices are "active" from the perspective of the passivity formalism. Interestingly, hybrid combinations of independently-variable-inertance inerters with non-negative variable-damping dampers can be designed to produce inherently-stable control systems. Following this framework, several published works on semi-active control systems are reviewed and classified. The presented methodology is useful when developing new devices. This is demonstrated by proposing a novel control device, which is classified and assessed in terms of inherent passivity. Moreover, this passivity assessment is conveniently used to propose a control law for the device. Finally, a frame structure controlled by the device is numerically simulated through a number of scenarios including instability and a countermeasure for its mitigation.
Mecánica Computacional, 2013
Mecánica Computacional, 2013
Resumen. En los últimos años, grandes esfuerzos se han llevado a cabo para desarrollar el concept... more Resumen. En los últimos años, grandes esfuerzos se han llevado a cabo para desarrollar el concepto de disipación de energía y plasmarlo en una tecnología aplicable, tanto en nuevas edificaciones como en la rehabilitación de estructuras existentes. Varios dispositivos basados en diferentes principios para disipar energía han sido desarrollados en todo el mundo. Una de las tareas más importantes para el diseñador es elegir el o los tipos de dispositivos a implementar y definir una distribución eficiente de los mismos. En el presente trabajo se realiza un análisis paramétrico de sistemas de disipación de energía mixtos, en los cuales se combinan disipadores viscosos (lineales) e histeréticos (no-lineales) diseñados a través de una metodología que permite determinar la distribución óptima de los mismos para lograr un desempeño deseado en estructuras bajo excitación sísmica. Para obtener resultados robustos, el análisis se realiza en el dominio de la frecuencia y la excitación se modela como un proceso estocástico estacionario caracterizado por una función de densidad espectral de potencia, compatible con el espectro de respuesta del lugar. En el problema de optimización, se considera como función objetivo a minimizar el costo total del sistema de disipación, tomando como parámetro el costo relativo entre el sistema viscoso y el histerético. El procedimiento es demostrado a través de ejemplos numéricos.
Journal of Vibration and Control, Jul 5, 2023
The tuned mass damper (TMD) is a classical device interesting for reducing deformations between D... more The tuned mass damper (TMD) is a classical device interesting for reducing deformations between DOFs without physically connecting them. However, it has a practical limit due to the increase in mass required for improving its performance. A building mass damper (BMD) uses mode coupling to make the upper substructure of a chain-like structure behave as a TMD for the lower substructure, which avoids adding mass to the structure. Unfortunately, near-uniform chain-like structures require isolation of the upper substructure for tuning the BMD, making it impractical for retrofitting existing structures since it is an in-series intervention. This paper proposes and evaluates using an inerter, instead of isolating the upper substructure, to control vibrations through mode coupling in a chain-like structure. From an analytical and numerical study, it was found a significant reduction of lower substructure deformations by implementing solely an inerter and a damper in the upper substructure. The inerter-based approach showed similar performance to the classical BMD with the advantage of being an in-parallel intervention. Therefore, this approach constitutes a practical retrofit to improve the dynamic behavior of existing structures with excessive deformations in a lower substructure whose functionality or esthetics would be compromised if control devices were installed in it.
Structural Health Monitoring-an International Journal, May 24, 2022
Structural Health Monitoring faces several challenges. Among them, especially for the quantificat... more Structural Health Monitoring faces several challenges. Among them, especially for the quantification of damage, are (1) the uncertainty in the boundary conditions, (2) the need for a calibrated numerical model, or measurements, of the structure in its healthy state, (3) the variability in the structure properties and boundary conditions due to environmental and operational conditions and (4) the possibility of damage in the virgin structure due to construction defects. Based on the sparsity condition of structural damage, this work presents a method that tackles these challenges simultaneously. The method consists in synthesising the response of a healthy-structure model, which is valid in the current environmental and operational conditions, only inside a region of interest (ROI) that excludes the boundaries and the rest of the full structure. This is accomplished by means of a robust regression of the solution of an analytical model of the healthy structure, and its loading, only using testing data of the (possibly) damaged structure in that ROI. Under ideal conditions, the method showed to be exact in detecting, locating and quantifying damage, in some cases much better than using measurements of the virgin structure. Finally, the method was tested by numerical simulations and using experimental data, under realistic conditions, which evidences its practical applicability.
Annals of Nuclear Energy, Oct 1, 2017
In this paper, a numerical study about the structural response of the Argentine nuclear power pla... more In this paper, a numerical study about the structural response of the Argentine nuclear power plant CAREM-25 subjected to the design basis accident (DBA) and seismic loads is presented. Taking into account the hardware capabilities available, a full 3D finite element model was adopted. A significant part of the building was modeled using more than 2 M solid elements. In order to take into account the foundation flexibility, linear springs were used. The springs and the model were calibrated against a greater model used to study the soil-structure interaction. The structure was subjected to the DBA and seismic loads as combinations defined by ASME international code. First, a transient thermal analysis was performed with the conditions defined by DBA and evaluating the time history of the temperature of the model, each 1 h until 36 h. The final results of this stage were considered as initial conditions of a static structural analysis including the pressure defined by DBA. Finally, an equivalent static analysis was performed to analyze the seismic response considering the design basis spectra for the site. The different loads were combined and the abnormal/extreme environmental combination was the most unfavorable for the structure, defining the design.
La seguridad de los tanques de almacenamiento de liquidos durante un terremoto es de vital import... more La seguridad de los tanques de almacenamiento de liquidos durante un terremoto es de vital importancia. Una de las tareas mas importantes para los ingenieros es determinar la respuesta dinamica de los contenedores en la forma mas precisa posible, de manera de lograr disenos eficientes y seguros. En este trabajo se evaluan diferentes modelos de tanques rectangulares contenedores de liquido bajo excitacion sismica. Un estudio comparativo se lleva a cabo considerando excitaciones con diferentes caracteristicas sobre tanques con distintas relaciones de esbeltez. La respuesta estructural se obtiene mediante: a) modelos simplificados en los cuales el comportamiento del liquido se representa por sistemas masa-resorte (modelo de Housner), b) modelos mas complejos basados en una aproximacion lagrangiana implementados en un codigo de elementos finitos y c) modelos experimentales que permiten validar y calibrar los modelos numericos. Si bien los resultados muestran una aceptable aproximacion d...
Con el objetivo de controlar el efecto de la accion sismica sobre las estructuras civiles se han ... more Con el objetivo de controlar el efecto de la accion sismica sobre las estructuras civiles se han desarrollado en los ultimos 40 anos diversas estrategias de control. Una de ellas consiste en el uso de amortiguadores de masa sintonizados (AMS). Las primeras aplicaciones de estos amortiguadores datan de principios del siglo XX, y han demostrado ser eficientes en mecanismos que funcionan bajo cargas armonicas de larga duracion, y en estructuras civiles sometidas a la accion del viento y sismo. El objetivo del presente trabajo es evaluar la efectividad en el uso de AMS sobre una estructura de un grado de libertad sometida a la accion de sismos de falla cercana. Este tipo de sismos se caracteriza por tener unos pocos pulsos de baja frecuencia y gran amplitud, con una duracion significativa reducida. Para evaluar el desempeno de los AMS se realizaron una serie de analisis experimentales sobre una estructura aporticada de un vano. La estructura fue ensayada, por medio de una mesa vibratori...
Engineering Structures, 2008
Vibration measurements in structures under ambient or controlled excitation open a way to damage ... more Vibration measurements in structures under ambient or controlled excitation open a way to damage assessment by correlating changes in the dynamic system parameters-natural frequencies, modal shapes or damping-with damage. Most methods proposed in the literature are based on the measurement of natural frequencies or modal shapes, associating damage to local reduction of the structural stiffness while completely ignoring damping, both in the identification procedure as well as in the correlation of changes in the spectral properties of the structure with damage. In numerous applications these methods, however, present some practical limitations on account of the low sensitivity of natural frequencies or modal shapes to damage. The main objective of this paper is to present a novel scheme to detect structural damage by means of the instantaneous damping coefficient identification using a wavelet transform. Laboratory tests as well as numerical simulations showed that in many commonly used structural systems damage causes important changes in damping. Thus, parameters that characterize structural damping can be used as damage-sensitive system properties. It is further shown that the wavelet transform can be conveniently employed in a procedure for instantaneous frequencies and damping identification from free vibration structural response.
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Papers by oscar curadelli