Elsa De Sa Caetano

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• Doctor of Engineering
• Professor (Full) at University of Porto

The paper discusses Structural Health Monitoring (SHM) techniques for evaluating the integrity of cable-stayed bridges. Specifically, it explores the application of numerical model updating to detect and quantify structural damage. The method involves modifying system properties to match numerical-experimental responses. Notable researchers have st...

Evolutionary game theory allows determining directly the solution of the maximum likelihood finite element model updating problem via the transformation of a bi-objective optimization problem into a game theory problem. The formulation of the updating problem as a game avoids the computation of the Pareto front and the solution of the subsequent de...

Evolutionary game theory allows determining directly the solution of the maximum likelihood finite element model updating problem via the transformation of a bi-objective optimization problem into a game theory problem. The formulation of the updating problem as a game avoids the computation of the Pareto front and the solution of the subsequent de...

This paper presents a study to evaluate the damping effectiveness of Stockbridge dampers on an overhead high-voltage transmission line conductor and their effects on estimating the corresponding fatigue lifetime. To increase the understanding of the dynamic behaviour of Stockbridge dampers, a test setup was designed and constructed to accommodate a...

Long-span cable-supported bridges, as critical civil infrastructure, underpin our transportation network. With the changing climate and escalating traffic volume, these bridges face functional and structural safety threats during their service life. Premature damages, such as cracks and corrosion, have the potential to lead to complete structural f...

The assessment of structural degradation from modal characteristics has a long tradition in engineering practice. For the specific case of bridge cables, such features (most notably, natural frequencies) are often employed in the identification of the installed axial force. However, low-order modal properties may be relatively insensitive to small,...

This article presents an experimental work developed in the context of the study of conductors’ fatigue due to the turbulent effect of wind on an overhead high-voltage transmission line. The research is centred on the laboratory study of a conductor segment with a 17 m length. The cable model, fitted with typical anchorages adopted in transmission...

This paper describes the use of the evolutionary game theory model to improve the finite-element model updating of civil engineering structures. For real-world applications, the finite element model updating problem is usually formulated via the maximum likelihood method. This method may transform the updating problem into two sub-problems: a bi-ob...

Stress-ribbon footbridges are often prone to excessive vibrations induced by environmental phenomena (e.g., wind) and human actions (e.g., walking). This paper studies a stress-ribbon footbridge at the Faculty of Engineering of the University of Porto (FEUP) in Portugal, where different degrees of vertical vibrations are perceptible in response to...

This report summarizes the discussion and the outcomes of a workshop held at the JRC in Ispra (Italy) on 6-7 June 2022, as part of the MITICA (Monitoring Transport Infrastructures with Connected and Automated vehicles) project. Considering the EU priority “A Europe fit for the digital age”, the workshop was dedicated to SHM and its application to c...

Fatigue is an important issue in the durability of long-span cable-supported bridges. These structures are submitted repetitively to loads such as strong winds, varying temperatures, and increasing roadway or railway traffic. The trainload accounts for a relatively significant portion of the fatigue of critical members. Usually, trains consist of d...

p>Trainloads play an essential role in the fatigue life of railway bridges as they cause important repetitive stress cycles at critical locations. Therefore, estimating such loads is relevant for preventive maintenance plans. This paper investigates an approach to detect trainloads using responses of the bridge, such as displacement and stress. Fir...

In long-span suspension bridges, premature failure of bearings or expansion joints has been a concern during the bridge service life. To implement a reasonable inspection strategy of these critical components, cumulative displacement must be considered for assessing their life consumption and health state. As suspension bridges are subjected to sim...

Slender footbridges are prone to excessive vibrations due to pedestrian effects, and comfort criteria often govern their design. In this sense, composite materials that combine high damping capacity with relatively high stiffness and low mass can provide functional benefits. This paper presents a study of the dynamic behaviour of an 11 m long hybri...

The paper discusses the main characteristics of some relevant cable structures and demonstrates that, generally, damage occurring in cables is best assessed using local measurements, including the installed force and mechanical properties. A review of techniques to evaluate force and mechanical properties is then illustrated with examples from prev...

The Éric Tabarly bridge in Nantes is a 210 m long cable-stayed road bridge crossing the Loire River, that was inaugurated in 2011. It is composed of a 27 m wide steel deck divided into two spans by a 57 m high steel pylon, being the main span 143 m long. In the context of the European Research Project DESDEMONA (DEtection of Steel DEfects by Enhanc...

p>This paper describes the experimental and numerical studies developed to assess the dynamic behaviour of a glass fibre reinforced polymer-concrete hybrid footbridge under pedestrian excitation. The analyses include an experimental assessment of the modal properties and the measurement of the dynamic bridge response to group loads. The numerical m...

In long‐span suspension bridges, fatigue is a significant concern for steel members as they are continuously under multiple effects such as wind, temperature, and traffic loads. Therefore, it is important to quantify the fatigue damage at critical details for effective maintenance countermeasures. This paper proposes an ensemble machine‐learning‐ba...

This paper aims at quantifying the uncertainties and their propagation effects in the numerical modelling of a cable-stayed bridge. To this purpose, the uncertainty quantification approach is implemented in a probabilistic finite element geometrically nonlinear elastic analysis performed in ANSYS®. The objective of this paper is to evaluate the imp...

Trains with a different number of carriages can induce stress responses with varying amplitudes in the long-span steel bridges, which consequently cause different levels of fatigue damage. To better evaluate the fatigue life of bridges, it is important to obtain the volume and types of different trains running on bridges. To overcome errors in iden...

This chapter focuses on the use of cables in cable-stayed and suspension bridges and comprises two major sections, one section containing a description of typical properties and characteristics of cables and associated components and a second section related to the analysis and design of cables and dampers. The two sections incorporate recommendati...

Over the last years, several studies have addressed the time-dependent mechanical behaviour of polymeric composites. When subjected to a constant stress, viscoelastic materials experience a time-dependent increase in strain. This phenomenon is known as viscoelastic creep and manifests as a tendency of a solid material to deform permanently under th...

The Laboratory of Vibrations and Structural Monitoring (ViBest, www.fe.up.pt/vibest) of CONSTRUCT/FEUP has been implementing, since 2007, a significant set of long-term dynamic monitoring systems in large Civil structures with different typologies (e.g. roadway, railway and pedestrian bridges, stadia suspension roofs, wind turbines, concrete dams o...

This work analyzes the difference in stiffness in a steel laboratory structure using clamped joints or bolted joints and analyzes if the stiffness varies in the same way when the frame is subjected to external dynamic loads that bring the joint materials to their yield strength. To make this comparison, the differences between clamp joint and bolte...

The use of glass fibre reinforced polymer (GFRP) composites in civil engineering structures has seen considerable growth in recent years due to their high strength, low self-weight, and corrosion resistance, namely when compared to traditional materials, such as steel and reinforced concrete. To enable the structural use of GFRP composite materials...

The analysis of the dynamic behavior of wind turbines is a complex task. These structures present diverse configurations, dependent on the wind conditions. Consequently, the dynamic behavior is highly dependent on their operating conditions. This paper analyzes the dynamic behavior of a 2.0 MW wind turbine during 1 year of operation. In that sense,...

p>This paper describes the studies conducted to assess damage in a sculpture. These include a numerical model and an ambient vibration test based on a dense mesh of points to identify the fundamental natural frequencies and the corresponding modal shapes. From the comparison between identified and calculated modal parameters, it was possible to ide...

Understanding and modeling the viscoelastic behavior of polymers and polymer-based materials for a wide range of quasistatic and high strain rates is of great interest for applications in which they are subjected to mechanical loads over a long time of operation, such as the self-weight or other static loads. The creep compliance and relaxation fun...

The accurate analysis of the behaviour of a polymeric composite structure, including the determination of its deformation over time and also the evaluation of its dynamic behaviour under service conditions, demands the characterisation of the viscoelastic properties of the constituent materials. Linear viscoelastic materials should be experimentall...

Artificial accelerograms are a very useful tool for designing structures against seismic hazards; in particular, when structures exhibit nonlinear behavior. This paper presents a Matlab code for generating artificial accelerograms to match code‐defined spectra based on the modification of actual earthquake ground motions. In this case, while the co...

The study of the human‐structure interaction (HSI) using biodynamics models has gained attention lately. Several studies have demonstrated that the passive (standing still) and active (bobbing/bouncing or walking) persons can act for the benefit of the structural system by considering their body dynamic properties. Nevertheless, little concern has...

In this paper, a biomechanical crowd‐structure interaction model is proposed and calibrated in order to take into account the change of the modal properties of footbridges in lateral direction induced by the pedestrian walking action. The model involves two submodels, namely, (a) the pedestrian‐structure interaction and (b) the crowd submodels. In...

In the current state of development, it is very hard to remotely evaluate the actual condition of wind turbines structures. This makes it impossible for a wind farm owner to correctly deliberate about the need of retrofitting the current wind turbine structure, as well as to decide about the possible extension of its operating lifetime. Taking into...

Historical old buildings bring together a whole set of unique characteristics with substantial influence on the acoustic behaviour, especially concerning the junctions between light and heavy elements, as is the case with wooden floors and stone masonry walls. The lack of information about the acoustic characteristics of wooden structures leads to...

In the context of fatigue evaluation of riveted railway bridges, cross-girder to main beam connections are frequently critical details. Secondary effects, such as out-of-plane bending and dynamic amplifications due to the proximity to loading paths which in the case of old bridges were not taken into account in the original design, may lead to seve...

This paper describes the work involving the implementation of a control system aimed at reducing vibrations in a slender footbridge located at FEUP campus. This structure was extensively studied in the past, mainly due to the clear exhibition of very perceptible vibrations induced by pedestrian loads. For that reason, a passive tuned mass damper (T...

This paper aims to characterise the properties of the atmospheric wind acting on a girder bridge crossing an abrupt volcanic breach at the Reunion Island, a zone frequently affected by cyclones. For that purpose, an aerodynamic monitoring system, comprising various anemometers, pressure and temperature sensors and accelerometers, is installed on th...

Tuned mass dampers (TMDs) are a well-established technology for passive structural vibration control involving harmonic vibrations. Some design issues are critical to guarantee the proper functioning of the device, in particular, the adequate tuning and the adequate space to accommodate the TMD stroke. With regard to the first aspect, semiactive TM...

With the goal of reducing the investment in monitoring equipment and simultaneously keep an adequate accuracy in structural condition assessment, this paper studies the results that can be obtained with different strategies of instrumentation of a 2.0 MW onshore wind turbine. The data processing strategy is based on the continuous tracking of the w...

Excessive vibration problems related to building floors concerning the human comfort have been reported by several researchers in the past two decades. The reason for those vibrations is mainly related with the current trend for the design of slender and flexible structural systems, with the inherent low damping. Consequently, such floors are prone...

This paper aims at stressing the major role that Dynamic Identification and Continuous Dynamic Monitoring can play in the observation and understanding of the structural behaviour of bridges along the different phases of their life cycle, based on the authors’ experience got at the Laboratory of Vibrations and Structural Monitoring (ViBest) of the...

In this paper a simplified biomechanical crowd-structure interaction model is proposed and validated in order to analyse the lateral lock-in phenomenon on real footbridges. The proposed crowd-structure interaction model is organized in three levels: (i) pedestrian-structure interaction; (ii) interaction among pedestrians in the crowd; and (iii) int...

Nowadays, the estimation of tensile forces in stay-cables or external tendons of Civil Engineering structures is required during periodic inspections. Among the available procedures, the ambient vibration testing (AVT) is recognized, in the scientific community, as an expedited technique. However, its accuracy is closely related to precise estimati...

Wind turbines are designed to last about 20 years. However, information regarding the actual structural condition of the wind turbine throughout this period is very limited or even null. This situation prevents the exploitation of the full potential of the support structure of the turbine, including the extension of its period of life. This paper p...

p>This paper investigates the effect of crowd walking in the dynamic response of a footbridge. For this purpose, the modal parameters of a single walking pedestrian are identified on the basis of the measurement of the applied load and body acceleration. These parameters are then extended to the characterization of a crowd. Noticing that the mass r...

In the context of the characterization of the shape of flying sails whilst racing, a novel method for real-time form-finding of flexural beams based on strain measurements has been developed and implemented. The very large displacements and deformations occurred on the beam pose specific demands both to the algorithm for shape detection and to the...

Este artigo apresenta um sistema de monitorização baseado em redes de sensores de deformação de fibra ótica utilizado para reconstruir a forma da vela de um barco em tempo real. O método desenvolvido é validado através de ensaios experimentais utilizando uma barra instrumentada com sensores de Bragg deformada em configurações correntes da forma da...

In the context of the characterization of the shape of flying sails whilst racing, a novel method for real-time shape reconstruction of flexural beams based on strain measurements has been developed and implemented. The very large displacements and deformations occurred on the beam pose specific demands both to the algorithm for shape detection and...

In Operational Modal Analysis (OMA) engineers are usually confronted with the challenge of extracting as much information as possible from the data collected in ambient vibration tests in order to characterize the modal behaviour of the tested structures under environmental and operational conditions. There exist several tools for this purpose that...

Considerable efforts have been made towards the development of robust and fully automated vibration-based monitoring systems with the goal of extracting relevant information regarding the dynamic behaviour and health condition of the monitored structure. Satisfactory results have been obtained in this scientific domain by combining accurate measure...

The flying shape detection of boat sails whilst racing may offer valuable insight into the sail design and performance. This paper describes a monitoring system based on fiber optic strain gauge sensors used to reconstruct in real time the form of a sail. For this purpose, a developed and implemented algorithm converts strain measurements into curv...

This chapter focuses on the use of cables in cable stayed and suspension bridges and comprehends two major sections, one containing a description of typical properties and characteristics of cables and associated components, and a second section related with the analysis and design of cables and dampers. The two sections incorporate recommendations...

Laboratory demonstration of a shape sensing monitoring system based on fiber-optic strain measurements.

Este artigo apresenta um sistema de monitorização baseado em redes de sensores de deformação de fibra ótica utilizado para reconstruir a forma da vela de um barco em tempo real. O método desenvolvido é validado através de ensaios experimentais utilizando uma barra instrumentada com sensores de Bragg deformada em configurações correntes da forma da...

The implementation of continuous dynamic monitoring systems in two bridges, in Portugal, is enabled to detect the occurrence of very significant environmental and operational effects on the modal properties of these bridges, based on automated processing of massive amounts of monitoring data collected by a set of accelerometers and thermal sensors...

Wind turbines are highly dynamic structural systems, prone to degradation along their expected lifetime of operation. In this context, dynamic monitoring systems represent a good option to continuously assess the condition of these structures. This paper presents the works performed to prepare the implementation of a dynamic monitoring system at a...

The paper describes two dynamic monitoring systems installed in lively footbridges with the purpose of characterizing the dynamic behavior and response of these structures and possibly detecting damage at early stages. Some monitoring results illustrate the capabilities of the presently existing technology.

This research aims at contributing to a better knowledge of the effects of wind on the structural behaviour of tension membrane structures. Considering the geometric nonlinearity of these structures, the form-finding procedure becomes important. Wind effects are then assessed considering the generation of stochastic wind loads and the numerical eva...

In this paper, a biomechanical crowd-structure interaction model is proposed and further implemented to adequately estimate the energy exchange between pedestrians and a footbridge. The proposed model focuses on the vibrations in the vertical direction, and it allows for taking into account the change of the modal properties of the structure due to...

The present application intends to provide real-time feedback about mechanical shapes in a boat with at least one sail. Disclosed are a method and system for acquiring sensor data about mechanical shapes using at least one pair of parallel optical fibers with shape sensors (1), a data processing system comprising an optical fiber interrogator devic...

Present traffic loads on bridges often exceed the actions anticipated at the time of construction. In Germany several prestressed concrete bridges with deficits in their load bearing capacity had been identified. An established retrofitting method is the installation of external tendons with deviation and anchorage blocks. Since the later proved to...

This paper characterizes the extensive research activity developed by the Laboratory ofVibrations and Structural Monitoring (ViBest) of FEUP in the fields of dynamic testing and continuous dynamic monitoring of long span bridges, briefly presenting results of some relevant applications as, for instance, the dynamic tests ofVasco da Gama Bridge, in...

In this work the modal parameters of a cable-stayed bridge with multiple measurement setups have been estimated using the Expectation-Maximization algorithm. First, the results of the proposed method have been compared to the results of the well-known Frequency Domain Decomposition method. In a second step, the method has been used to estimate the...

The paper describes two dynamic monitoring systems installed in civil engineering structures, a footbridge and a suspended stadium roof. These systems are used for characterization of environmental and operational effects and, in the limit, for the early detection of damage. Some examples of collected data and results are presented.

The demo will focus on two dynamic monitoring systems installed in footbridges with the purpose of characterizing the dynamic behavior and response of these structures and possibly detecting damage at early stages.

The paper describes the implementation of a dynamic monitoring system at a 2.0 MW onshore wind turbine. The system is composed by two components aiming at the structural integrity and fatigue assessment. The first component enables the continuous tracking of modal characteristics of the wind turbine (natural frequency values, modal damping ratios a...

The paper discusses the role of dynamic testing in the study of cable structures. In this context, the identification of cable force based on vibration measurements is discussed. Vibration and damping assessment are then introduced as the focus of dynamic monitoring systems, and particular aspects of the structural behaviour under environmental loa...

This paper presents the strategy adopted to automatically track the variation of the modal parameters of an onshore wind turbine equipped with a dynamic monitoring system in operation for more than one year. The processing is based on state-of-the art parametric operational modal analysis algorithms, such as SSI-COV, SSI-DATA and p-LSCF, that are c...

This paper aims at presenting and discussing the strategies for updating the finite element numerical modelling of stone masonry arch bridges using operational modal analysis. The study comprehended three bridges: two old ones, the St. Lázaro and the Lagoncinha bridges, and a recently constructed bridge in Vila Fria, Portugal. Updating of the bridg...

The fatigue behaviour of steel railway bridges is a complex phenomenon. On the one side, the Engineer must face the problem of dynamic amplification of the loads and their randomness, on the other side, the fatigue resistance is highly dependent on the load itself, since for different stress levels the material can sustain different number of cycle...

This paper describes a monitoring system installed at the Grande Ravine viaduct, in Reunion Island, and presents results of the analysis of the data recorded during a 2-year period. These include a characterisation of the wind based on the identification of predominant wind directions, incidence and mean velocity, as well as on local wind turbulenc...

This paper describes the numerical and experimental dynamic studies developed during structural design and after construction of the new footbridge over the Ave River in Santo Tirso, Portugal, as well as the results obtained over a year with the installed permanent monitoring system. The bridge is composed by a steel arch, with a 60m central span a...

A new moveable footbridge was recently built at the entrance of Marina Atlantico in the city of Viana do Castelo, Portugal. This paper presents a brief description of the global solution, with a special focus on the characterisation of the construction methods adopted. Particular consideration is given to the construction of the pivot pylon and the...

The London 2012 Olympic Stadium roof was constructed as a cable net covered by a flat PVC-coated polyester fabric membrane supported by an oval compression truss and an inner tension ring. As part of the geometric and mechanical control of the constructed structure, the forces installed in the most relevant cables were assessed using the vibration...