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- Avaliação comparativa da regulamentação para estruturas offshore no dimensionamento de elementos tubulares circulares em aço (ISO 19902 e EC3)Publication . Manco, Tiago; Martins, João Pedro; Rigueiro, Constança; Silva, Luís Simões daO objectivo deste artigo é efectuar uma análise comparativa de normas no dimensionamento de estruturas offshore com foco em elementos circulares tubulares em aço. Pretende concluir-se acerca do conservadorismo associado a dois grupos de normas: offshore vs. construção. Para tal, a capacidade resistente obtida pela ISO 19902 será confrontada com a obtida pelo Eurocódigo 3 (que não contém indicações específicas para estas estruturas) através da parte 1-1 e 1-6. Por fim, estas resistências serão comparadas com uma análise numérica para esforços de compressão e pressão hidrostática, concluindo-se que ambas as partes do EC3 podem, de uma forma geral, ser aplicadas a estruturas offshore.
- Numerical validation of t-stub componente subject to impact loadPublication . Ribeiro, João; Rigueiro, Constança; Santiago, AldinaAccidental loadings due to blast or impact may easily cause failure of the elements that are exposed or located in the vicinity of the hazard, leading in some cases, to the progressive collapse of the whole structure; therefore, assessment of the structural over strength is critical for structural engineers to ensure a certain level of security and validate alternative unloading paths. The T-stub model is used to describe the behaviour of components i) “column flange in bending” and ii) “endplate in bending” usually present in a beam-to-column bending resistant connection [1]. These components are responsible for the behaviour in the tension zone of connections, being able to provide ductility to a connection; thus, proper characterization of T-stub behaviour under impact loading is crucial. In this paper, a 3D finite element model exploring the behaviour of a welded T-stub with flange thickness of 10 mm (T-10) (Fig. 1) is validated against experimental results from: i) one quasi-static loading (reference case) (grey dotted line Fig. 2 and Fig. 4); ii) and two rapidly applied dynamic loadings according to the gas pressure in the chamber: a. 120 Bar (Impact #1 - T10-D120-160 - Fig. 2); and b. 160 Bar (Impact #1 - T10-D160 - Fig. 4) [2]. The steel grade of the T-stub is S355 and the bolts M20 grade 8.8 are fully threaded. The dynamic loading simulations take into account the elevated strain rate effects in the stress enhancement, based on dynamic increase factors, following the Johnson-Cook material model [3]. The dynamic loadings are applied as a boundary condition in the “pull out surface” (Fig. 1) considering the Tstub’s transient displacement responses obtained from experimental tests; maximum displacement values are reached in approximately 0.08 sec. The accuracy of the numerical force-displacement predictions for both quasi-static and dynamic loading schemes confirms that the Johnson-Cook material model used, provide accurate stress enhancement to describe the behaviour of bolted steel connections subject to impact loadings. From Fig. 2 and Fig. 4, it can be observed that the elastic stiffness remains unchanged for all loading schemes: ki = 180 kN/m, as the steel’s elastic modulus introduced in the numerical models are the same for both quasi-static and dynamic situations; moreover, the strain rates developed are similar for both dynamic loading (Fig. 3), inducing the same dynamic increase factors for the stress enhancement; the F-δ flows are therefore, similar for both numerical dynamic responses but with different failure displacements. Plastic resistances of the T-stub: FRd,quasi-static = 161 kN and FRd,120 Bar = FRd,160 Bar = 195 kN; corresponding to an enhancement of +21% of the plastic resistance due to the elevated strain rate effects. Fig. 3 illustrates the pattern of the strain rate (ER), ranging from 1/s to 3/s in the plastic hinge developed next to the weld toe, corresponding to a DIFs of 1.27 and 1.31. Furthermore, comparison of the equivalent plastic strain (PEEQ) pattern for both loading situations, shows that two plastic hinges are developed per flange leg, consistently with the plastic failure mode type 1 predicted by the Eurocode 3, part 1.8 [1]. However, in the dynamic case, the plastic hinges are slightly underdeveloped and higher strains are required in the bolt to meet the same deformation level.
- Comportamento dinâmico de pontes ferroviárias com plataforma balastradaPublication . Rigueiro, Constança; Rebelo, Carlos; Silva, Luís Simões da; Heiden, Marko; Pircher, MartinNeste estudo procede-se à caracterização de dois modelos dinâmicos de plataformas ferroviárias balastradas e faz-se a sua implementação num modelo de elementos finitos de uma ponte. Efectua-se a análise dinâmica da referida ponte, com e sem plataforma balastrada, quando sujeita a um comboio ICE. Medições efectuadas a várias pontes com plataforma balastrada, permitiu fazer a aplicação dos modelos a uma situação real de uma ponte ferroviária e comparar os resultados com os valores medidos. Por último aplicaram-se os métodos simplificados DER e LIV, que estimam o valor máximo dos deslocamentos e das acelerações nas velocidades próximas da ressonância.
- Proceedings of the 5th International Conference on Production Economics and Project EvaluationPublication . Farinha, Luís; Araújo, Madalena; Rigueiro, Constança; Raposo, Daniel; Neves, João Vasco; Anjos, O.; Dionísio, Rogério PaisInternational Conference on Production Economics and Project Evaluation.
- Material modelling of tensile steel component under impulsive loadingPublication . Ribeiro, João; Santiago, Aldina; Rigueiro, ConstançaThe “T-stub” model is used in Eurocode 3 – part 1.8 as part of the “component method” for the representation of steel connection’s tension zone and is usually responsible for providing ductility to the connection. Looking forward to establish the “T-stub’s” maximum displacement capacity, fracture simulation of steel elements is here explored following “element deletion” technique for a given level of ductile damage. Material softening and triaxial stress state dependency are assessed based on finite element analysis of common uniaxial tension tests. Numerical model describing the “T-stub” behaviour and displacement capacity are compared against experimental tests of statically loaded “T-stub” specimens with thicknesses of 10 and 15 mm. Based on the calibrated FE model for monotonic loading, the behaviour of this tensile component is evaluated for impulsive loading regimes. The material behaviour is improved to take into account the possible development of elevated strain rates based on results from Split-Hopkinson Bar tests, through the incorporation of the Johnson-Cook’s elevated strain rate law for material strain-hardening description.
- Modelling the interaction effects of the high-speed train-track-bridge system using ADINAPublication . Rigueiro, Constança; Rebelo, Carlos; Silva, Luís Simões daThe main purpose of this paper is to present some results concerning the investigation of the effects of the vehicle-bridge interaction in simply supported medium span viaducts, including the modelling of the ballast-rail track system. This system is modelled using the rail stiffness in vertical and longitudinal directions, including the rail pad and the sleepers, and the ballast as a system of vertical springs, dampers and masses. A simplified vehicle model proposed by the European Railway Research Institute (ERRI D214, 1999), taking into account the vehicle primary suspension characteristics and the mass of the bogie is used with the contact algorithm implemented in the software ADINA to evaluate the response acceleration of a simply supported medium span concrete viaduct. The results are compared with those from the moving loads model for a wide range of train speeds
- Relação entre o aproveitamento no ensino secundário e no ensino superiorPublication . Ferreira, Ana Vaz; Daniel, Ana Cristina Marques; Ramos, George; Cravo, Ivone Teresa Gregório; Rigueiro, Constança; Rei, Constantino Mendes; Amado, Jorge Manuel Pascoal"Dentro do actual quadro português no que respeita ao (in)sucesso educativo, convém salientar as elevadas taxas de abandono e de retenção do Ensino Superior assim como a metodologia utilizada para o ingresso no mesmo ensino - numerus clausus, classificações mínimas, provas específicas, ... . Esta situação obriga a que se perceba que é urgente o incremento da cultura educativa ao nível do Ensino Secundário e Ensino Superior, o que só se poderá alcançar pela resolução dos problemas de eficiência que caracterizam esses dois patamares de Ensino. Neste contexto, interessa compreender por que razão as exigências de aprendizagem no Ensino Superior reflectem de forma tão flagrante lacunas formativas ao nível do Ensino Secundário e até que ponto esse grau de exigência não é o resultado de pedagogias orientadas para o primado enciclopédico e não para o desejável desenvolvimento intelectual do aluno, quer enquanto futuro profissional quer enquanto cidadão. Factores como a influência social, o ambiente sócio-económico e cultural envolvente do aluno são também objecto de análise no presente trabalho."
- Development of an experimental system to apply high rates of loadingPublication . Barata, Pedro; Santiago, Aldina; Rodrigues, João Paulo; Rigueiro, ConstançaThe work presented in this paper is part of an ongoing research project at the University of Coimbra IMPACTFIRE PTDC/ECM/110807/2009, which the main focus is the characterization of the behaviour of bolted steel connections subjected to accidental loads, such as impact and fire. Detailed description of the experimental parts developed, designed and fabricated at University of Coimbra, to carry out tests under high rates of loading is presented. This experimental part is operated by high pressure nitrogen comprising three main components: pneumatic reservoir, pneumatic cylinder and a rapidly opening valve, which allows the instantaneous nitrogen flow from the reservoir to the cylinder. Furthermore, the data acquisition system, the methodology for analysis of the results and the results of preliminary tests are also reported.
- Numerical assessment of T-Stub component subject to impact loadingPublication . Ribeiro, João; Rigueiro, Constança; Santiago, AldinaSince the partial collapse of the Ronan Point apartment in London in 1968, requirements for the avoidance of disproportionate collapse are addressed in the design codes. Despite these requirements, the ability of steel connections to sustain large tensile forces whilst undergoing significant rotations has been questioned by recent studies and real evidences (as for example the collapse of the WTC towers in 2001). A point raised in FEMA’s report is: “Connection performance under impact loads… needs to be analytically understood and quantified for improved design capabilities and performance as critical components in structural frames”. Additionally, a recent report presented by Arup made the following recommendation (rec. nº 26): “… the strain rate enhancement of yield strengths in connections could still be important. It is recommended that research is undertaken to examine this effect using rate-sensitive material models”. Ductility of joints under accidental loadings, such as impact and fire are being investigated in the scope of the FCT project “IMPACTFIRE”, at the University of Coimbra. This paper presents and describes the results of a finite element model for the characterization of: i) the nonlinear behaviour of a bolted t-stub component under impact loading and ii) its strain-rate sensitivity. In order to identify relevant parameters that influence the dynamic behaviour of the t-stub, the effect of the loading magnitude, the effect of t-stub thickness and advantages of using implicit or explicit integration procedures are also studied.
- Experimental dynamic evaluation of the Guarda footbridgePublication . Rebelo, Carlos; Pircher, Martin; Rigueiro, Constança; Silva, Luís Simões daThis paper deals with the methodologies used for footbridges design and their application to a steel footbridge built over a road junction in Guarda, Portugal. The complexity of the bridge behavior and the high uncertainty connected with the damping and natural frequencies estimation supported the decision to carry out vibration measurements included in the commissioning tests. A modal identification was performed and a FE model of the bridge was updated accordingly. Tests with pedestrians were also performed in order to gain as much information as possible towards the final decision to be made concerning the installation or not of the foreseen tuned mass dampers. Tests included continuous streaming of pedestrian groups with increasing size crossing the bridge in synchronized walking at various pace rates.