Numerical assessment of T-Stub component subject to impact loading

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

Material modelling of tensile steel component under impulsive loading

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

Análise dinâmica não linear de ligações viga-pilar aparafusadas com placa de extremidade

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

T-stub model under impact load – numerical model validation

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.ABSTRACT: This article presents the validation of a finite element model developed to study the non-linear dynamic response of the T-stub model. The T-stub model is used in the “component method” to establish the behaviour of components contributing the most for a joint’s ductility, namely the “end-plate” in bending. The numerical model is built with the software ABAQUS and validated against experimental tests under quasi-static and short transient dynamic loads. The study comprises welded T-stubs with flange thicknesses of 10 and 15 mm made of steel S355 and bolted with M20’s class 8.8. The numerical model takes into account possible elevated strain rate effects according to material characterization performed with compressive Spilt Hopkinson Bar tests at 600 s-

Numerical validation of t-stub componente subject to impact load

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

Cost/benefit analysis in the implementation of sustainable construction principles in a residential building

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 developed 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 sustainability 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

Post-impact fire resistence of t-stub joint component:numerical evaluation

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

Dynamic behaviour of timber footbridges

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

Vibration of the railway track-viaduct system under moving vehicles taking into account the interaction effec

Avaliação dos efeitos dinâmicos em pontes ferroviárias de alta velocidade de pequeno e médio vão

A presente tese teve como principal objectivo ir ao encontro das recomendações propostas nos vários relatórios da Comissão de Especialistas D214 do ERRI, nomeadamente a necessidade da realização e interpretação de ensaios experimentais e de medições em condições normais de serviço a fim de confrontar e validar os resultados de aplicação das diferentes metodologias e averiguar os efeitos que influenciam o comportamento dinâmico de pontes de pequeno e médio vão. As pontes ferroviárias, com vãos inferiores a 40 m, para o tráfego de alta velocidade com velocidades superiores a 200 km/h são estruturas muito sensíveis aos efeitos dinâmicos, para melhor compreensão do comportamento dinâmico deste tipo de estruturas inicialmente são apresentados alguns parâmetros que o influenciam. A realização de uma campanha de medições em vários viadutos ferroviários de pequeno e médio vão permitiu a identificação dos parâmetros modais das estruturas, frequências próprias e amortecimentos, bem como a medição de acelerações verticais no tabuleiro das pontes quando sujeitas à passagem do tráfego real. Numa avaliação numérica preliminar verificou-se que num número significativo de estruturas, a aceleração vertical máxima do tabuleiro ultrapassava o valor limite de 0,35g chegando a alcançar os 20 m/s2. A caracterização modal dos viadutos, os modos de vibração, frequências próprias e amortecimentos permitiram o desenvolvimento de modelos de elementos finitos cujos comportamentos foram validados com a comparação das respostas de acelerações verticais obtidas nas medições. Os modelos de elementos finitos incluem uma série de factores que condicionam o seu comportamento, tais como as condições de fronteira dos tabuleiros, a continuidade do carril sobre os apoios, a distribuição longitudinal na via das forças verticais dos eixos dos comboios. Na modelação da via férrea sobre a estrutura três modelos dinâmicos foram utilizados, modelos que resultam de investigações efectuadas quer no domínio do comportamento da via, do comportamento dos veículos que sobre ela circulam e da ponte que lhe serve de apoio. Diferentes metodologias foram utilizadas para o cálculo das respostas das pontes, numéricas e simplificadas. As metodologias numéricas compreendem a aplicação das forças rolantes e a interacção entre o veículo e a ponte, algoritmo de contacto. Para ambas as metodologias é descrita a sua implementação e validação no software ADINA. Vários algoritmos de integração passo a passo foram aplicados, o método da Sobreposição Modal, o método de Newmark e o método de Wilson-θ. As metodologias simplificadas, os métodos da Decomposição da Excitação em Ressonância (DER) e da Linha de Influência Residual ou Virtual (LIR ou LIV), também foram expostas e implementadas de forma a comparar os seus resultados com os derivados da aplicação dos métodos de integração passo a passo. Com base no modelo de elementos finitos desenvolvido veículo/via férrea/ponte procurou-se também averiguar a influência das irregularidades da via no comportamento dinâmico de pontes de médio vão. Considerou-se dois tipos de irregularidades: a irregularidade isolada posicionada a meio vão da ponte, simulação de uma má compactação do balastro; e a irregularidade aleatória contínua, posicionada em toda a extensão do carril. A avaliação dos efeitos derivados da consideração de irregularidades aleatórias na via férrea é efectuada recorrendo à técnica de Monte-Carlo, em que diversos perfis de irregularidades são utilizados, gerados a partir de funções densidade espectral de potência de irregularidades da via férrea correspondentes às diversas classes de qualidade da via. As respostas máximas da ponte com as diferentes irregularidades foram determinadas, bem como as respostas dos veículos, as forças de contacto entre a roda e o carril e as acelerações verticais na massa vibrante do balastro da via