Formulaçao pelo método dos residuos pesados de um elemento finito de nós coincidentes para modelar a transferencia de calor na interface de contacto entre dois meios distintos

Faz-se a formulas50 pelo método dos resíduos pesados de um elemento finito de nós coincidentes que permite modelar a transmissiio de calor através da interface de contacto entre dois meios distintos. A modelaqiio daquela interface obriga & utilizas50 de elementos finitos de espessura extremamente reduzida, os quais siio por vezes, responsáveis pela ocorr6ncia de instabilidades numéricas. Pretende-se com o elemento finito especial de nós coincidentes evitar o aparecimento de problemas de mau condicionamento numérico. Comparam-se os resultados obtidos com este elemento com os que se obt6m com o elemento quadrático de 8 nós e com os resultados de outros autores, em problemas de conduq5o de calor, mostrando-se as vantagens da sua aplicaqçao.A weighted residual formulation of a finite element with coincident nodes has been done to model the heat transfer at the contact interface between two distinct mediums. The finite element modelling of that interface requires the use of very thin elements, which are responsible for some numerical instabilities. With the special finite element with coincident nodes we pretend to avoid the occurence of this numerical ill-conditioning. The results obtained with this special finite element, in heat conduction problems, are compared with those obtained with the height node quadric element and with the result from other authors and the advantage of its use is shown.Peer Reviewe

Stainless steel plate girders subjected to shear buckling at normal and elevated temperatures

The final publication is available at Springer via http://dx.doi.org/10.1007/s10694-016-0602-6Numerical simulations have been widely applied, for the determination of the resistance of steel structural elements, when experimental analysis are not possible (due to cost or size limitations) or when parametric studies with high number of variables are needed. However, the numerical models must be properly validated with experimental tests in order to deliver reliable studies. With the purpose of studying the behaviour of stainless steel plate girders in fire situation, a total of 34 experimental tests from the literature have been numerically modelled. The tested girders had different configurations: rigid and non-rigid end posts, 2 and 4 panels, and transversal and longitudinal stiffeners were considered. Comparative analyses between those experimental and numerical results have been done. Good approximations to the experimental results at normal temperatures have been achieved with differences on average lower than 5%. Afterwards, the developed numerical model has been used to perform a sensitivity analysis on the influence of the initial geometric imperfections at both normal and elevated temperatures, considering different values for its maximum amplitudes, concluding that 10% of the web thickness is an appropriate value for the maximum amplitude of the geometric imperfections when modelling experimental tests. The effect of the residual stresses has also been analysed, being obtained differences lower than 2%. Finally, comparisons between the numerical results and the Eurocode 3 design procedures have been performed considering different uniform elevated temperatures.Peer ReviewedPostprint (author's final draft

Lateral Torsional Buckling of Steel I-Beams in Case of Fire – Numerical Modelling

peer reviewedaudience: researche

GEM – A SOFTWARE FOR STABILITY VERIFICATION OF NON-UNIFORM MEMBERS, Adaptation of the general method procedure to fire design

There is currently no specific rules in Part 1-2 of Eurocode 3 for the stability verification of non-uniform members under fire conditions. For normal temperature, Part 1-1 of the same code provides a General Method to check the stability against lateral and lateral-torsional buckling for these type of members, though it requires some extensive calculations. It is here demonstrated in this paper how both problems can be addressed, by exposing a procedure that accounts for the modifications of the method at elevated temperatures, and by showing its implementation within a computer program. It is also shown how the program can be used to assess the study of the method itself, by applying it to a case of a web-tapered beam-column and comparing it to numerical results

ANALYSIS OF STEEL STRUCTURAL MEMBERS IN FIRE WITH SLENDER CROSS-SECTIONS THROUGH BEAM FINITE ELEMENTS APPLYING AN EFFECTIVE CONSTITUTIVE LAW

Steel profiles with slender cross-sections are characterized by their high susceptibility to instability phenomena, especially local buckling, which are intensified under fire conditions. This work presents a study on numerical modelling of the behaviour of steel structural elements in case of fire with slender cross-sections. To accurately carry out these analyses it is necessary to take into account those local instability modes, which normally is only possible with shell finite elements. However, aiming at the development of more expeditious methods, particularly important for analysing complete structures in case of fire, recent studies have proposed the use of beam finite elements considering the presence of local buckling through the implementation of a new effective steel constitutive law. The objective of this work is to develop a study to validate this methodology using the program SAFIR. Comparisons are made between the results obtained applying the referred new methodology and finite element analyses using shell elements. The studies were made to laterally restrained beams, unrestrained beams, axially compressed columns and columns subjected to bending plus compression

SHEAR BUCKLING EVALUATION IN STEEL PLATE GIRDERS WITH RIGID END POSTS SUBJECTED TO ELEVATED TEMPERATURES

The current study intends to analyse the behaviour of steel plate girders with rigid end posts subjected to elevated temperatures, aiming the assessment of the ultimate shear strength in case of fire. A parametric numerical study was performed involving a wide range of cross-section’s dimensions, plate girders’ aspect ratios and steel grades. Plate girders were numerically tested at both normal and elevated temperature, being considered three different uniform temperatures. The influence of the geometrical imperfections, as well as the residual stresses, was taken into account. Finally, the numerical results were compared to the Eurocode 3 (EC3) prescriptions, adapted to fire situation by the direct application of the reduction factors for the stress-strain relationship of steel at elevated temperatures. It was shown that the EC3 design rules should be improved because they are not conservative, conducting to unsafe results

PARAMETRIC STUDY ON THE LATERAL TORSIONAL BUCKLING OF STAINLESS STEEL I BEAMS WITH CLASS 4 CROSS-SECTIONS IN CASE OF FIRE

For predicting the behaviour of beams with thin-walled I sections, named Class 4 in Eurocode 3 (EC3), it is necessary to account for the occurrence of both local and lateral torsional buckling (LTB). These instability phenomena, which are intensified at elevated temperatures, should be accurately considered in design rules. The fire design guidelines for stainless steel members, given in Part 1-2 of EC3, propose the use of the same formulae developed for carbon steel (CS) elements. However, these two materials have different constitutive laws, leading to believe that the use of those formulae should be validated. This work presents a parametric numerical study on the behaviour of stainless steel beams with Class 4 I sections at elevated temperatures. The influences of several parameters such as stainless steel grade, loading type and cross section slenderness are evaluated, and comparisons between the obtained numerical results and EC3 rules are presented

PARAMETRIC STUDY ON THE FIRE RESISTANCE OF STEEL COLUMNS WITH COLD-FORMED LIPPED CHANNEL SECTIONS

Steel structural elements with cold-formed thin-walled sections are becoming increasingly common in buildings due to their lightness and ability to support large spans. In these members, local, distortional and global instabilities are important common failure modes. At high temperatures, these instability phenomena are intensified. This paper presents a numerical study on the behaviour of columns with cold-formed C-sections in case of fire when subjected to compression. A parametric study, considering different steel grades, temperatures and different cross-sections with different slendernesses, is presented. Comparisons are also made between the numerical results and analytical design rules, such as the EN1993-1-2, using its Annex E or its French National Annex, where a different constitutive law is recommended for cold-formed profiles. It is possible to conclude that the simple calculation rules are on the safe side but sometimes too conservative

Numerical modelling of steel plate girders at normal and elevated temperatures

The main goal of this study is to increase the knowledge on the behaviour of steel plate girders subjected to shear buckling at both normal and elevated temperatures. Hence, numerical models were duly validated with experimental tests from the literature. Experimental tests on steel plate girders with different configurations were numerically reproduced, showing a good agreement between numerical and experimental results. Afterwards, applying the validated numerical models, sensitivity analyses on the influence of initial imperfections were performed. Different values for the maximum amplitude of geometric imperfections were considered and residual stresses were also taken into account. Finally, the effect of the end supports configuration was also studied aiming to understand the strength enhancement given by the rigid end support at normal temperature and evaluating if that strength enhancement is maintained in case of fire.Peer ReviewedPostprint (author's final draft

Analysis of stress and strain in a rotating disk mounted on a rigid shaft

The plane state of stress in an elastic-perfectly plastic isotropic rotating annular disk mounted on a rigid shaft is studied. The analysis of stresses, strains and displacements within the disk of constant thickness and density is based on the Mises yield criterion and its associated flow rule. It is observed that the plastic deformation is localized in the vicinity of the inner radius of the disk, and the disk of a sufficiently large outer radius never becomes fully plastic. The semi-analytical method of stress-strain analysis developed is illustrated by some numerical examples.