elsa caetano | Universidade do Porto (original) (raw)

Books by elsa caetano

The fifty years of experience of construction of cable-stayed bridges since their establishment a... more The fifty years of experience of construction of cable-stayed bridges since their establishment as a new category among the classical types have brought an immense progress, ranging from design and conception to materials, analysis, construction, observation and retrofitting. The growing construction of cable-stayed bridges has also triggered researchers’ and designers’ attention to the problem of cable vibrations.
Intensive research has been developed all over the world during the last two decades as a consequence of the numerous cases of cable vibrations exhibited by all types of cable-stayed bridges.
Despite the increased knowledge of the various vibration phenomena, most of the outcomes and research results have been published in journals and conference proceedings and scarce information is currently provided by the existing recommendations and codes.
The present book provides a comprehensive survey on the governing phenomena of cable vibration, both associated with direct action of wind and rain: buffeting, vortex-shedding, wake effects, rain-wind vibration; and resulting from the indirect excitation through anchorage oscillation: external and parametric excitation. Methodologies for assessment of the effects of those phenomena are presented and illustrated by practical examples. Control of cable vibrations is then discussed and state-of-art results on the design of passive control devices are presented.
The book is complemented with a series of case reports reflecting the practical approach shared by experienced designers and consultants: Yves Bournand (VSL International), Chris Geurts (TNO), Carl Hansvold (Johs. Holt), Allan Larsen (Cowi) and Randall Poston (WDP & Associates).

The current trend for construction of footbridges marked by increased lightness and slenderness h... more The current trend for construction of footbridges marked by increased lightness and slenderness has brought new requirements into design. In effect, despite the small loads associated with pedestrian action, two episodes of large vibrations in two landmark footbridges, the Millenium bridge in London, and the Solférino bridge in Paris, have shown the importance of dynamic effects in these long span bridges and the need to develop methodologies for their assessment and control.
The intensive research developed during the last decade on the topic of human-induced vibrations in footbridges is now getting more accredited by the establishment of design guidelines and recommendations.
This volume is a collection of 10 invited contributions by eminent experts and results from the workshop "Footbridge vibration design: worldwide experience", held during the 3rd International Footbridge Conference, July 2008, in Porto, Portugal, and organised by the Faculty of Engineering of the University of Porto in conjunction with the Technical Advisory Bureau for Steel Users ConstruirAcier.
The book is addressed to Civil and Mechanical Engineers involved in design and research and aims to transfer current knowledge of footbridge dynamic design in an applied, practical way. It is divided in two parts, one focusing on the presentation and discussion of guidelines and numerical/ experimental tools to assist design, and a second part, related with practical experience in dynamic design of footbridges and control of vibrations.

Papers by elsa caetano

The development of efficient vibration based structural health monitoring systems requires distin... more The development of efficient vibration based structural health monitoring systems requires distinguishing between abnormal changes in modal parameters caused by structural damage and normal changes due to varying environmental conditions. In this context, this paper is focused on the analysis and extraction of effects of temperature oscillations on natural frequencies of a footbridge, where a long-term dynamic monitoring system was installed by the Laboratory of Vibrations and Monitoring of the Faculty of Engineering of University of Porto. With that purpose, firstly, the temperature influence on the natural frequencies is reported, and correlations between measured temperatures and estimated natural frequencies are analyzed. Then, the Principal Component Analysis (PCA) and the Novelty Detection method are applied to identified natural frequencies: PCA effectively eliminates environmental influence; Novelty analysis on the residual error of PCA predicted model is used as a statistical indication of damage. The proposed procedure is illustrated using continuous dynamic data collected from the footbridge during more than one year. 56 IOMAC'09 – 3 International Operational Modal Analysis Conference 2 DESCRIPTION OF THE BRIDGE AND DYNAMIC MONITORING SYSTEM The new “Pedro e Inês” footbridge over Mondego River is located in the centre of the City Park of Coimbra, recently developed along the two banks of the river and opened to public in April 2007. This new infrastructure, conceived to become a landmark for the city and to contribute to the quality of a new leisure area, was designed by Adão da Fonseca (Adão da Fonseca et al 2005), leading a team from AFAssociados, in collaboration with Cecil Balmond, leading the architectural team from Ove Arup. The bridge has a total length of 275m and is formed by a parabolic central arch with a span of 110m and two half lateral arches, in steel, supporting with total continuity a composite steel concrete deck (Fig.1). The anti-symmetry of both arch and deck cross-sections along the longitudinal axis of the bridge is a unique feature of this bridge, leading to the creation of a central square with 8m×8m at mid-span. (a) Bridge plan and elevation, deployment of accelerometers and sections (S1-S3) with temperature sensors (b) Sections (S1-S3) and temperature sensors Figure 1. Deployment of accelerometers and temperature sensors Numerical and experimental studies, developed by the Laboratory of Vibration and Monitoring from FEUP, showed that this slender footbridge is prone to excessive vibrations caused by groups or streams of pedestrians. Therefore, six groups of tuned mass dampers (TMDs) were installed (Caetano, Cunha et al 2008). Aiming the permanent characterization of vibration levels after construction, the footbridge was also instrumented with a dynamic monitoring system, formed by signal acquisition, data communication and signal processing modules. The signal acquisition system comprises six uniaxial piezoelectric accelerometers installed in correspondence with the location of TMDs (Fig. 1). Five of them measure vertical accelerations (AV1-AV3, AV5-AV6), whereas another one measures lateral vibrations at mid-span (AT4). All sensors are mounted inside the metallic deck and wired to the corresponding signal conditioners and digital computer incorporating an analogue to digital converter and a UPS system, located in one of the concrete abutments of the structure. An automatic signal acquisition toolkit was developed in LabVIEW environment to record the acceleration signals and generate setup files every 20 minutes. The data communication system sends permanently the most recent collected data to a computer located at FEUP using an ADSL line (Moutinho et al 2008). The signal processing system is a toolkit developed in LabVIEW. It automatically searches the latest data transmitted from the bridge in 30.5 0m 64.00 m 55.00 m 55.00 m 64.00 m 6.00 m AV1 AV2 AV3 AV5 AV6

This paper is related to the work involving the numerical and experimental dynamic analysis of a ... more This paper is related to the work involving the numerical and experimental dynamic analysis of a very flexible pedestrian bridge located in Porto. Given the high level of vibrations reported by the users of that structure, the Laboratory of Vibrations and Structural Monitoring (www.fe.up.pt/vibest) from Faculty of Engineering of University of Porto (FEUP) became interested in this case, following the previous work of this research group in this area of Civil Engineering. In a first stage, the structure is described and the identified dynamic properties are listed. Then, experimental and numerical simulations of several scenarios of pedestrian loads exciting the bridge are presented. Given the "lively" behavior of the structure, it was decided to install a dynamic monitoring system in order to characterize the effective levels of vibration experienced by that structure during long periods of time. The results of the dynamic monitoring are exposed in this paper, which gives reason to the actual existence of complaints from pedestrians.

$Research paper thumbnail of Fatigue analysis of a railway bridge based on fracture mechanics and local modelling of riveted connections$

Engineering Failure Analysis, Dec 1, 2018

In the context of fatigue evaluation of riveted railway bridges, cross-girder to main beam connec... more 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 severe increase of fatigue damage. The fatigue assessment of old riveted railway bridges has been addressed in the last years by developing local models of critical riveted joints that are linked to global models. This localglobal modelling approach aims at evaluating local secondary stresses. Former fatigue probabilistic analyses of riveted joints have been focused on resistance variability rather than on loading/stresses (actions) variability. In this paper a probabilistic procedure to include the variability of loading in the fatigue analysis of complex riveted joints of railway bridges is proposed assuming loading as a random variable. Local finite element models were developed and later coupled with the global model in order to obtain the real stresses associated to real trains crossing the bridge. To reduce computational time, the results obtained from these local models were inputted in a Linear Fracture Mechanics model, supported by Paris fatigue crack propagation law. Monte Carlo simulation technique was applied to calculate the fatigue reliability of an old riveted railway bridge, considering traffic records from previous studies on the bridge.

Springer eBooks, Jun 16, 2022

The Éric Tabarly bridge in Nantes is a 210m long cable-stayed road bridge crossing the Loire Rive... more The Éric Tabarly bridge in Nantes is a 210m 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 143m long. In the context of the European Research Project DESDEMONA (DEtection of Steel DEfects by Enhanced MONitoring and Automated procedure for self-inspection and maintenance), the bridge has been equipped with a dynamic monitoring system, constituted of 16 uniaxial accelerometers installed both on the deck and on the Pylon, with accelerations being recorded with a sampling rate of 100 Hz. This paper describes the dynamic monitoring system installed in the bridge and the results achieved during the first months of operation, including the characterization of vibration levels (maximum and effective values) as well as the automatic identification of the bridge modal properties. Finally, the effects of operational and environmental conditions on modal properties are studied.

Footbridge 2022, Madrid: Creating Experience, Oct 7, 2021

The current paper describes the structure and the dynamic behaviour of a footbridge built in Serr... more The current paper describes the structure and the dynamic behaviour of a footbridge built in Serralves Park at Porto, Portugal. The footbridge, named Tree Top Walk, is located in a slope in the park at the height of the top of the trees. Because it is in a slope, the footbridge develops with an irregular U-shape at a constant level. The total length of the footbridge is approximately 250 m. At its highest level, the height is 15 m.Approximately at one third of the course there is a passage between the two branches of the U. At this zone, there is a staircase that allows to reach the footbridge at the middle of its course, from the woods and a small amphitheatre at a level of 14 m. The structure of the deck is made with timber while the columns are made with steel covered with timber across their height and the connection between the columns and the deck is performed with timber struts placed in the longitudinal and transversal directions. Three of the columns are made with a circular profile, while the others are 4-foot tubes connected at the top by a circular tube with2.35 m length. The deck is made with four longitudinal girders with a cross section of 8x52 cm. Spans have different lengths, ranging from 5 to 14,34 m. In total there are 23 spans and 22 columns. In the structural analysis, dead loads, live loads, wind and earthquake actions were considered. To assess the dynamic behaviour of the structure, dynamic tests have been carried out. The performed tests include an ambient vibration test, the determination of the damping level and tests with pedestrians.

THE INTERNATIONAL JOURNAL OF COMPUTATIONAL METHODS AND EXPERIMENTAL MEASUREMENTS, Nov 3, 2017

In this paper a simplified biomechanical crowd-structure interaction model is proposed and valida... more 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) interaction between the crowd and the structure. To this end, first, the human-structure interaction of each pedestrian is modelled via a simplified two degrees of freedom system. Second, the interaction among pedestrians inside the crowd is simulated using a multi-agent model. The considered model simulates the movement of each pedestrian from the dynamic equilibrium of the different social forces that act on him/her. Finally, the crowd-structure interaction is achieved modifying the behaviour of the pedestrians depending on the comfort level experienced. For this purpose, the recommendations established by the French standards have been considered. The integration of the three levels in an overall model is achieved by the implementation of a predictivecorrective method. The performance of the proposed model is validated correlating the numerical and experimental dynamic response of the Pedro e Inês footbridge during the development of a lateral lock-in pedestrian test. As the first lateral natural frequency of the footbridge is inside the range that characterizes the walking pedestrian step frequency in lateral direction, numerical and experimental studies were performed to analyse its behaviour under pedestrian action. The agreement between the numerical and experimental results is adequate. However, further studies are recommended in order to generalize the proposed approach and facilitate its use during the design project of future footbridges.

Structural Control and Health Monitoring

Footbridge 2022, Madrid: Creating Experience

This paper describes the experimental and numerical studies developed to assess the dynamic behav... more 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 modelling of pedestrian effects evidences the difficulty in reproducing the loads applied to the footbridge and the need to consider the third and fourth harmonics of the walking frequency in the applied loads to reproduce the measured response accurately. Furthermore, by comparison with the simulation results of pedestrian effects on an equivalent length structure made of steel, it is shown that the GFRP-concrete structure possesses a higher dissipation capacity and a more favourable dynamic behaviour.

Seismic Design Practice into the Next Century

Proceedings of the 7th International Conference on Computational Methods in Structural Dynamics and Earthquake Engineering (COMPDYN 2015), 2019

The Laboratory of Vibrations and Structural Monitoring (ViBest, www.fe.up.pt/vibest) of CONSTRUCT... more 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 or high voltage transmission lines). This paper briefly describes some of these applications, showing the interest and potential of the developed technology, as well as of the huge high quality database created, which can be used for joint collaborative research at European level.

Proceedings of the 5th International Conference on Computational Methods in Structural Dynamics and Earthquake Engineering (COMPDYN 2015), 2015

The paper presents recent results from a research project based on a continuous dynamic monitorin... more The paper presents recent results from a research project based on a continuous dynamic monitoring of a wind turbine. The monitoring system was developed with the capacity to detect structural abnormalities based on the continuous tracking of the modal properties of wind turbines (natural frequencies, modal damping ratios and mode shapes). In addition, the system is also capable to estimate the dynamic stress levels of the tower structure, in order to assess the damage condition and evaluate its remaining fatigue life. In the first part of the present paper, preliminary results from one year of continuous tracking of the modal properties of the wind turbine vibration modes are introduced. The main characteristics of the tracked modes are shown and the evolution of these modes with rotor rotation speed is characterized. In a second part, the methodology followed to evaluate the stress condition of the wind turbine tower is introduced. This procedure is illustrated and validated with the help of a numerical analysis of a wind turbine, developed in the HAWC2 aeroelastic code.

Lecture Notes in Civil Engineering, 2021

Maintenance, Safety, Risk, Management and Life-Cycle Performance of Bridges, 2018

Smart Structures and Systems, 2021

The great availability of measurement systems permits to acquire quite easily data related to str... more The great availability of measurement systems permits to acquire quite easily data related to structural oscillations in operational conditions. This occurrence may permit to enhance our capability to data-driven computing using directly experimental data and pertinent constraints and conservation laws, such as compatibility and equilibrium, surely certain. In the paper, a methodology will be presented to furnish an analytical mechanical model of a suspension bridge in which the main parameters can be derived from vibration measurements. In this respect, Polymax and Enhanced Frequency Domain Decomposition identification procedures are used to determine a complete modal model which is used to evaluate an error function. Optimization algorithms are used to evaluate the function minima in the fundamental parameter space. The procedure will be validated by results coming from a sophisticated finite element model for which geometric measurements are included through a 3D point cloud geom...