A crowd-structure interaction model to analyze the lateral lock-in phenomenon on footbridges

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 predictive– corrective 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.Ministerio de Ciencia DPI2014-53947-

Vibration assessment of the International Guadiana Bridge

The paper describes the development of a monitoring program for a cable-stayed bridge and resumes the major dynamic properties identified from a series of test campaigns conducted on the bridge, which are also correlated with results from a numerical analysis. Some aspects of the current dynamic behavior of the bridge under ambient excitation are discussed, considering in particular the large cable vibrations that are frequently observed

Representações sociais do envelhecimento ativo num olhar genderizado

O objetivo deste estudo é analisar as representações sociais do envelhecimento ativo, procurando detetar os impactos das conceções diferenciadas de homens e mulheres idosos. Foi desenvolvido um estudo de coorte transversal. Foram inquiridas 123 pessoas idosas (M=76,84; DP=8,46). Utilizámos para aceder às evocações sobre o envelhecimento ativo a Técnica de Associação Livre de Palavras. As representações que emergiram com maior frequência foram a “família”, “passeio”, “convívio” e “saúde”. Foi possível destacar diferenças na representação social do envelhecimento ativo a partir de um olhar genderizado. Das evocações exclusivas do sexo masculino a evocação proeminente ancora no “desporto”, enquanto no sexo feminino a “atividade doméstica” predomina. Ambos os sexos elegeram a “família” como evocação proeminente na representação social do envelhecimento ativo. As mulheres, refletindo os papéis que desempenharam ao longo da sua vida parecem assumir que um envelhecimento ativo representa a execução das tarefas que sempre fizeram, centrando-se muitas das suas evocações em conteúdos de cariz familista, onde o papel de cuidadoras se destaca. As atividades de carácter instrumental e associadas à esfera privada, como as tarefas domésticas emergem com maior proeminência. No caso dos homens, a componente familista é também evocada, emergindo concomitantemente atividades de lazer.The aim of this study is to analyse the social representations of active ageing, in order to detect the impacts of the diferente conceptions by older women and men. We developed a cross-sectional cohort study and 123 older people were surveyed (M=76,84; SD=8.46). We accessed the evocations on active ageing through the Technique of Free Association of words. The representations that most frequently emerged were the “family”, “walk”, “living” and “health”. It was also possible to highlight differences in the social representation of active ageing from a gendered perspective. As exclusive evocations, the male prominente evocation anchors in "sport", while among females the “domestic activity” predominated. Interpersonal relationships, in particular those established with the family network, are central to various phases of life cycle. The model of social protection dominant during the dictatorship period (Estado Novo), pointing out the family as the central pillar of protection, seems crystallized throughout time. Both genders chose the “family” as prominent evocation as a social representation of active ageing. Although in Western society the social status of women has changed, women in our sample seem to assume that active ageing is associated with the execution of tasks they have always done, focusing many of its evocations in a family oriented content, where the role of caregivers stands out. This reflects the gender roles. Instrumental activities and those that are associated to private sphere, such as domestic tasks, are emerging more prominently. In the case of men, the family components also emerged, but at the same time as pleasurable leisure activities.(undefined

Damping identification in a stress-ribbon footbridge

This paper describes the different types of dynamic tests (hammer, shaker, free and ambient vibration tests) recently performed on the stress-ribbon footbridge of FEUP Campus, with the purpose of achieving an accurate identification of the most significant modal parameters, getting better sensitivity with regard to the advantages and drawbacks associated to the application of the alternative identification techniques employed. Due to the enormous influence that damping has on the structural simulated response under pedestrian loads, particular attention has been dedicated to the identification of modal damping factors

Cable-deck dynamic interactions at the International Guadiana Bridge: On-site measurements and finite element modelling

SUMMARY The International Guadiana Bridge is a cable-stayed bridge crossing the Guadiana River, which marks the southern border between Portugal and Spain. The bridge has a central span of 324 m and a total length of 666 m and was open to traffic in 1991. Despite the globally satisfying behaviour under the common environmental loads, which largely ensures the bridge serviceability, frequent episodes of cable vibration have been observed since completion of the construction. In this paper, the bridge modal properties and dynamic behaviour, identified from repeated campaigns of vibration data acquisitions, are compared with the response of a three-dimensional finite element model, including the description of the cable transversal motion. The model, after minor updating, furnishes a realistic reproduction of the current bridge dynamic behaviour. Then different possible justifications of the local vibrations are evaluated, briefly scanning the known sources of large amplitude cable oscillations both in the linear and the nonlinear field. In particular, the occurrence of different internal resonance conditions is deeply discussed, in order to verify whether the experimental observations could be really justified by a cable–deck dynamic interaction mechanism. Among different possibilities, a beating phenomenon between two resonant modes, amplified by the lower damping and inertial characteristics of the local mode with respect to the global one, is selected as the most critical cable excitation source. Since the cable vibrations are proved to persist for different wind conditions, the heavy traffic load on the bridge deck is investigated as one possible source of the global mode direct excitation. On this respect, the model response to random load and moving forces acting on the bridge deck is numerically evaluated evidencing how some particular features of the real bridge behaviour can be qualitatively reproduced. Copyright # 2008 John Wiley & Sons, Ltd

Ambient vibration re-testing and operational modal analysis of the Humber Bridge

Author's manuscript version. The final published version is available via the publisher at doi:10.1016/j.engstruct.2010.02.034. Copyright © 2010 Elsevier Ltd. All rights reserved.An ambient vibration survey of the Humber Bridge was carried out in July 2008 by a combined team from the UK, Portugal and Hong Kong. The exercise had several purposes that included the evaluation of current technology for instrumentation and system identification and the generation of an experimental data set of modal properties to be used for validation and updating of finite element models for scenario simulation and structural health monitoring. The exercise was conducted as part of a project aimed at developing online diagnosis capabilities for three landmark European suspension bridges. Ten stand-alone triaxial acceleration recorders were deployed at locations along all three spans and in all four pylons during five days of consecutive one-hour recordings. Time series segments from the recorders were merged, and several operational modal analysis techniques were used to analyse these data and assemble modal models representing the global behavior of the bridge in all three dimensions for all components of the structure. The paper describes the equipment and procedures used for the exercise, compares the operational modal analysis (OMA) technology used for system identification and presents modal parameters for key vibration modes of the complete structure. Results obtained using three techniques: natural excitation technique/eignsystem realization algorithm, stochastic subspace identification and p-LSCF, are compared among themselves and with those obtained from a 1985 test of the bridge, showing few significant modal parameter changes over 23 years in cases where direct comparison is possible The measurement system and the much more sophisticated OMA technology used in the present test show clear advantages necessary due to the compressed timescales compared to the earlier exercise. Even so, the parameter estimates exhibit significant variability between different methods and variations of the same method, while also varying in time and having inherent variability.Engineering and Physical Sciences Research Council (EPSRC

Trends in Business Cycles Synchronization in the EMU

The synchronization of business cycles is associated with optimal currency areas. Being a prerequisite for membership in such a zone was questioned by the view that the synchronization of economic cycles would result from the very operation of the optimal currency zone. An empirical observation of the business cycles in the Eurozone seems, however, to show that this synchronization has not increased, especially in relation to the so-called peripheral countries, which of course raises questions about that association. The chapter therefore seeks to verify whether the synchronization of the business cycles of the Eurozone countries has actually increased or, if it has decreased, in which countries this has taken place

From Input-Output to Output-Only Modal Identification of Civil Engineering Structures

This paper presents a brief characterization of the evolution of Experimental Modal Analysis in theCivil Engineering field, from Input-Output to Output-Only Modal Identification Techniques, takingparticularly into account the experience of the authors at the Laboratory of Vibrations andMonitoring (VIBEST, www.fe.up.pt/vibest) of FEUP