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In ENV1995-2:1997 (Eurocode 5-Part 2), a simplified method is proposed for checking the serviceability limit state (SLS) of vibration in timber bridges subjected to the action of streams of pedestrians. The procedure estimates the values of peak acceleration in the deck under such conditions. This paper undertakes a comparison between the values supplied by that method and those obtained through a Finite-Element based numerical analysis. A number of load cases is analysed, in which variable values of the number of pedestrians and of its walking frequency is considered. The probabilistic models used to generate the dynamic loading corresponding to these crowds are also described.
Vibration of the railway track-viaduct system under moving vehicles taking into account the interaction effect
Este artigo apresenta a validação de um modelo numérico para o estudo da resposta dinâmica não-linear de T-stub’s, desenvolvido com o software ABAQUS. O T-stub é usado no “método das componentes” para definição da resposta das componentes que mais contribuem para a ductilidade de ligações metálicas aparafusadas, nomeadamente a chapa de extremidade em flexão. O comportamento numérico do T-stub é validado recorrendo aos resultados obtidos em ensaios experimentais sob regime quase estático e também sob carregamentos dinâmicos de curta duração. Neste estudo são considerados T-stub’s soldados com banzos de espessura 10 e 15 mm em aço S355 e parafusos de dimensão M20 e de classe 8.8. O modelo numérico inclui a representação dos efeitos de possíveis taxas de deformação elevadas, com base na caracterização do material a partir de testes de Split Hopkinson Bar em compressão com uma taxa de deformação de 600 s-1.
The construction sector is one of the major contributors for the increase of pollution and environmental degradation. The uncontrolled increase on the consumption of natural resources, the way they are used and the high emissions they arise, are impelling the study and implementation of policies and procedures which ensure a sustainable future for construction and for the sustainability of the planet. The objective of this paper is to present the work devel-oped in order to assess and optimize the sustainability of a residential building at the design stage, through the application of a sustainability assessment tool, SBToolPT-H. A first evaluation was done, when conventional solutions were adopted. After this, a proposal was developed with several improvements in order to create a sustainable building that corresponds to the Portuguese best practices. This case study was developed taking into account the twenty-five sus-tainability indicators of the SBToolPT-H assessment system. Additionally, dynamic thermal simulation was used in order to support the optimization of the thermal performance and the indoor thermal comfort.
Accidental 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.
O presente artigo apresenta uma avaliação numérica do comportamento de ligações aparafusadas com placa de extremidade, sujeitas a carregamentos de impacto. O modelo numérico foi previamente validado com os resultados de ensaios experimentais das mesmas ligações quando sujeitas a carregamentos estáticos. Este modelo foi desenvolvido no software ABAQUS, recorrendo a algoritmos de integração directa para a determinação da resposta da ligação quando solicitada por uma força instantânea. Dos resultados obtidos, concluiu-se que a ligação estudada quando sujeita a carregamentos dinâmicos apresenta uma maior capacidade resistente e que o seu modo de rotura tende para modos de roturas com menor ductilidade.
The “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.
Current paper presents a finite element analyses for the characterization of the nonlinear behaviour of bolted t-stub component subject to impact loading followed by fire. The proposed numerical model has previously validated against experimental results under monotonic static loading at ambient and elevated temperatures (Ribeiro et al., 2013). 3D solid and contact elements from the finite element package Abaqus are used to perform the structural model. The temperature dependent material properties, the geometrical and material nonlinearities (including the strain rate sensitivity) were taken into account to predict the failure of the t-stub. A parametric study was conducted to to provide insight into the overall behavior, namely their stiffness, resistance, ductility and failure modes due to the effects of dynamic loading followed by fire.
Since 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.
Na Parte 2 do Eurocódigo 5 é proposto, para tipologias correntes, um processo simplificado de verificação do estado-limite de vibração para pontes de madeira sujeitas à acção de grupos de peões, o qual utiliza estimativas do valor máximo da aceleração no tabuleiro. Neste trabalho procede-se à comparação entre os valores determinados por esse método e os obtidos por análise dinâmica de modelos numéricos de Elementos Finitos, sob a acção de grupos de peões de dimensão e frequência de passada variáveis. Descrevem-se ainda os modelos probabilísticos utilizados na geração do carregamento dinâmico correspondente a estes grupos.
The paper reports on the results of the modal identification of several small to medium span railway viaducts. The identification was based mainly on the free vibration of each structure immediately after the train passages. The non-linear behavior of some components, namely the ballast and the aged bearing supports, conditioned the evolution of the free vibration signals, which showed increasing values for the eigenfrequencies and lower values for the damping as far as the vibration amplitude decreased. An estimate for the ballast shear stiffness and for the influence of the superstructure (track plus ballast) in the overall dynamic behaviour could also be obtained from the measurements evaluation.
The 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
Due to the need for increasing train speeds several existing small to medium span bridges in the track Linz-Wels (Austria) were re-evaluated. In a preliminary numerical calculation, considering conservative values for the dynamic parameters, very high vertical accelerations were computed for some of those structures. An experimental program was thus carried out in order to get a better estimation for the dynamic behaviour of the bridges, concerning mainly the first vertical eigenfrequency and the corresponding viscous damping. The paper reports on the results of this experimental investigation and identifies some areas where further research is necessary.
This 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.
Railway track irregularities consist of a deviation of the inside edge of the rail from the ideal geometric rail contour and may occur even during the passage of the vehicle at a very low speed. Track irregularities can influence the dynamic behaviour of railways bridges and increase dynamic load effects. This paper addresses the influence of different irregularities on the dynamic behaviour of a medium span bridge. Random irregularities, continuous all over the rail, are considered. The maximum response of the bridge, displacements and accelerations, at the mid span is calculated. For these calculations the dynamic model of the ballast track, present in the ERRI studies, is used and the response of the ballast is also analysed.
The main purpose of this paper is to present some results concerning the investigation that has been done by the authors regarding the dynamic response of small to médium span railway bridges using response acceleration data colleted during the measurements carried out on single span bridges on the railway track Linz-Wels, in Austria. Using output-only methods in this experimental program, it was possible to have an estimation of the igenfrequencies, mode shapes and the corresponding viscous damping. Due to the fact that the bridges were of the same type some generalizations concerning their structural behavior was possible and finite element models were calibrated in order to compute responses for real traffic. The numerical model of the bridges takes into account the track and the real boundary conditions of the decks. The measured and the computed acceleration responses of the track/bridge system are compared using two methods: the moving forces method and the interaction vehicle/track/bridge method.
O comportamento dinâmico de pontes ferroviárias de alta velocidade é um dos principais aspectos a ter em conta no dimensionamento deste tipo de estruturas. Um dos parâmetros que é mais crítico em pontes de um único vão é o relativo às acelerações máximas verticais. Valores excessivos de acelerações podem por em causa a segurança da circulação na via, nomeadamente a instabilidade do balastro e o conforto dos passageiros. Este artigo tem como objectivo apresentar o trabalho de investigação desenvolvido em pontes ferroviárias de médio vão. O recurso à identificação modal de casos de estudo permitiu desenvolver modelos de elementos finitos capazes de simular o comportamento dinâmico em situação de serviço. Por outro lado tendo como base o modelo de elementos finitos desenvolvido veículo/via-férrea ponte foi analisado a influência das irregularidades verticais da via no comportamento das pontes.
As irregularidades na via-férrea influenciam o comportamento dinâmico das pontes ferroviárias e aumentam os efeitos dinâmicos produzidos pela passagem dos eixos do comboio. Neste estudo é analisada a influência das irregularidades da via-férrea na resposta dinâmica de uma ponte, cuja primeira frequência natural de vibração se encontra sobre os limites definidos no Eurocódigo 1. São consideradas diferentes irregularidades, isolada a meio-vão e contínua de amplitude aleatória existente em toda a extensão do carril. As respostas máximas da ponte com as irregularidades são determinadas em termos de deslocamentos e acelerações, e comparadas com as obtidas sem as irregularidades. Recorre-se ao modelo dinâmico de via-férrea balastrada ERRI. São analisadas as acelerações na massa vibrante do balastro via-férrea bem como as forças de contacto entre a roda e o carril.
The main purpose of this work is to evaluate and compare the dynamic response of a ballasted single-span simply supported viaduct using available models for the track system composed by the rails, the sleepers and the ballast. The dynamic response obtained from field measurements is used to establish the dynamic characteristics of the structure and the real traffic response acceleration to be used as reference for the comparisons. For the numeric calculations two types of loading model are considered, namely the moving forces model and the interaction bridge/track/vehicle model.
Neste artigo apresenta-se a calibração do modelo estrutural de uma ponte ferroviária com um vão simplesmente apoiado de 23.5 metros em betão pré-esforçado, para a qual se possuem medições da resposta de aceleração vertical do tabuleiro quando sujeita à passagem de tráfego real. O estudo é complementado com o cálculo e comparação da resposta dinâmica da ponte quando sujeita à passagem de dois tipos de composição ferroviária: uma locomotiva e o comboio de alta velocidade alemão ICE2. Nesta análise são definidas duas metodologias para o cálculo da resposta, nomeadamente, o modelo das forças rolantes e a interacção do sistema veículo/via férrea/ponte em que são utilizados três diferentes modelos dinâmicos de via férrea.
Neste artigo apresenta-se um programa experimental em T-stubs sujeitos a cargas de impacto. O modelo do T-stub é utilizado para a avaliar o comportamento das componentes, existentes na zona tracionada da ligação, sendo estas as que mais contribuem para a ductilidade das ligações. As principais variáveis aqui estudadas são a espessura do banzo do T-stub (10 e 15 mm) e a intensidade da carga de impacto. Os resultados dos ensaios dos T-stubs, quando sujeitos a cargas de impacto, evidenciam um aumento da resistência plástica e uma diminuição da deformação do T-stub quando comparados com os dos ensaios quase estáticos.
Neste artigo são apresentados os resultados obtidos numa campanha de ensaios dinâmicos realizados para a avaliação estrutural da ponte de Odemira no decorrer das obras de reabilitação e reforço. Estes ensaios foram efectuados de modo a determinar as frequências próprias, as configurações dos modos de vibração e os amortecimentos modais. Foram realizadas medições de vibração forçada e de vibração ambiental, tendo sido adquiridas acelerações verticais e horizontais, segundo a direcção transversal e a direcção longitudinal, nos três primeiros tramos da Ponte de Odemira adjacentes à margem esquerda do rio Mira. Neste artigo efectua-se a comparação dos resultados obtidos do modelo numérico de elementos finitos com os resultados dos ensaios experimentais. Este tipo de ensaios de identificação modal é frequentemente utilizado para a inspecção e diagnóstico de estruturas, nomeadamente por exemplo, na averiguação da rigidez da estrutura, de zonas com potenciais anomalias e das condições de fronteira da estrutura, e podem ocorrer nas diferentes fases da vida útil da estrutura, construção e reabilitação.
After the accidents occurred during the first decade of this millennium, such as the World Trade Center (2001), London (2005) and Madrid (2004), special attention was given to the study of robust structures subjected to different accidental loads. The World Trade Center attack highlighted troublesome weakness in connections, which exhibited poor performance caused by brittle failure. Structural details played a very significant behavioural role when the structure is subjected to impulsive loads [1]. Concerning the behaviour of steel joint, the literature presents several studies on steel connections under both static and cyclic loads [2, 3]; many results of these studies have contributed for improving the current standards, such as the Eurocode 3, part 1-8 [4]. However, only scarce information exists concerning the behaviour of these joints directly loaded by higher loading rates [5]. This paper is devoted to the report of an experimental programme on steel joints under impact loading, in particular to the assessment of T-stub response under tension. The T-stub is used to evaluate the behaviour of the tensile components that are responsible for the deformability of the joint, such as the end plate in bending. Firstly, the paper describes the features of an experimental system developed at the University of Coimbra, to apply high rates of loading; then, it presents the experimental campaign and the corresponding results. The test apparatus is defined by a rigid reaction frame fixed to a reaction slab and connected to a rigid “flying beam” (HEM 340, S355J2); the impact force is applied in this beam through a pneumatic driven cylinder ( = 125 mm). This “flying beam” consists in a second class lever pivot located at the opposite end of the cylinder location, and the tested specimen is subjected to the dynamic force at the middle of this beam. The pneumatic cylinder was designed to work with a maximum operating pressure of 30 MPa. During the impact tests, force, displacements, accelerations and strains are measured. Because this type of tests occurs in a very short time intervals (hundredths of a second), specific equipment with large sample rate are used. The experimental programme includes two impact tests on welded T-stubs: i) test T-10-D120-160 - rapidly applied loading of 120 Bar [12 MPa], followed by 160 Bar [16 MPa]; and ii) test T-10-D160 - rapidly applied loading of a single impact equal to 160 Bar [16 MPa]. The results of these tests are compared against reference quasi-static tests [6]. The T-stub geometry is defined by two plates, the flange and the web, both with 10 mm of thickness and welded by means of a continuous 45º fillet. The flange is bolted through two bolts M20, grade 8.8 fully threaded.
The 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.
Neste 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.
O 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.
O desenvolvimento sustentável na atualidade, está intrinsecamente associado ao crescimento populacional e á relação de habitabilidade – espaço urbano; tendo como objectivo a preservação do meio ambiente e a correta gestão de recursos naturais. Por tal motivo a América Latina é uma região com grandes desafios e capacidades no âmbito do desenvolvimento sustentável, isto deve-se á presença de uma das maiores taxas de urbanização do mundo. Nas últimas décadas, as comunidades Latino americanas incorporaram ideias e programas cuja finalidade foi impulsionar o desenvolvimento urbano sustentável e salvaguardar o património. Sem embargo ainda se apresentam problemas sem solução, como a contaminação, a deterioração ambiental, o detrimento dos factores sociais, a pobreza extrema, entre outros. Grande parte desta situação, deve-se á maioria das propostas impulsadas, não promovem soluções que alcancem abordagens viáveis que logram perceber as necessidades reais de estas comunidades; portanto, esses programas não conseguem atender ou resolver todas as exigências da sociedade. Para contribuir na busca de soluções e projetos que detonem o desenvolvimento sustentável na América Latina, este artigo foi criado, que funciona como um guia para suscitar a reflexão sobre a forma de vida destas comunidades e promove uma visão pragmática através de um conhecimento mais profundo das necessidades, carências e problemáticas que atualmente se criam nestas sociedades. Apresentando como caso de estudo a cidade de Santiago de Querétaro, México para mostrar e exemplificar as problemáticas expostas.
No presente artigo apresenta-se o comportamento mecânico de ligações de perfis tubulares comumente utilizados em estruturas offshore. As normas Norsok N-004, ISO 19902 e Eurocódigo 3 (EC3) Parte 1-8 são utilizadas para a determinação da resistência das ligações. Diferentes configurações de ligações planares são utilizadas, nomeadamente X, Y e K. Uma análise elásto-plástica das ligações é efectuada recorrendo a um software comercial de elementos finitos, determinando-se curvas força/deslocamento e momento/rotação. Este estudo permite concluir que as normas determinam valores conservadores para reduzidos valores de esbelteza dos tubos e que a utilização do EC3 está condicionada aos limites indicados na norma.