Wyniki wyszukiwania - Biblioteka Nauki

1

Numerical and experimental approaches of masonry arches effected by horizontal springing displacements

100%

Lamblin D. , Van Parys L. , Descamps T.

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tom No. 7

201-213

EN

Masonry arches arc efficient structural systems that have been used for centuries in important constructions. Since some of them have been sensitively affected by structural pathologies, it can be difficult for engineers to assess the remaining stability of the structure. The numerical simulation of this kind of problem often constitutes an interesting approach whose crucial point is the modelling of the interface between the vous-soirs. This paper proposes a simplified Finite Element modelling using virtual truss bars exhibiting a non-linear behaviour. After the description of the procedure, the paper presents three classical approaches that can be used in order to validate the results obtained with the simplified one: limit analysis theory, finite element simulation performed in a general framework, and a lab test campaign. An original complementary approach based on a multi-body system formulation has also been described. Key results obtained with the different approaches have been compared briefly for a case study.

2

Applications of evolutionary strategies in optimal design of mechanical systems

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Datoussaid S. , Guerlement G. , Descamps T.

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tom No. 7

35-51

EN

This paper is concerned with the optimization of structural systems. On one hand it concerns the kinematic or dynamic behaviour of multibody systems. On the other hand it concerns the minimum weight desmg of frames according to static and dynamic constraints. The authors first recall the classical form of an optimization problem, whose purpose is to find the set of design variables which minimizes a given objective function while verifying potentialconstraints. After recalling the principal optimization techniques, the evolutionary strategies are presented in detail. They are inspired from the natural evolution: the genes of individuals mutate from generation to generation and the survivings are those being the best fitted to their environment. The analogy with an optimization problem is quite straightforward: a set of design variables can be considered as the genes of an individual and the value of the objective function for this set of design variables represents the fitness for survival of the corresponding individual. Practically, the mutation is performed by modifying the design variables of μ parents, according to a normal distribution with zero as average and gives rise to offsprings whose best μ individuals form the new parent population. The paper gives some indica tions for the choice of the principal parameters or options and explains how to manage the mutation in order to control the speed of convergence. The performances of the evolutionary strategies are then illustrated by three examples: the structural optimization of a two-storey steel frame, the kinematic optimization of a suspension and the dynamic optimization of the comfort of a railway vehicle. Evolutionary strategies, although slower than hill-climbing methods, arc an interesting alternative. They indeed have several advantages: the optimization engine remains completely independent of the simulation one and can be adapted to any field of engineering, they are very robust and converge to global and not local optimal solutions.

3

Historic timber roofs modelling: prosthesis and resin repairs

88%

Descamps T. , Avez C. , Carpentier O. , Antczak E. , Jeong G. Y.

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tom Nr 47

52--60

EN

Current standards mainly focus on modern dowel type joints and usually provide little guidance to designers regarding traditional joints. An effective timber repair needs a complex interdisciplinary work with careful investigation and execution. In the field of restoration of patrimonial buildings, engineers have to work with old structures made of badly preserved timber elements connected by particular connections known as “traditional connections”. The joints play a major role in the structural behaviour of the old timber frames. Further studies in the area are deemed necessary to establish a reliable design specification, the protocol of the repair procedure, and recommendations for the future rehabilitation or strengthening interventions. Patrimonial timber roofs are of considerable historic and aesthetic significance, and demand a thorough understanding of the principles and techniques involved to choose a suitable repair strategy. When restoring a beam with a prosthesis, a continuity joint between the prosthesis and the sound parts of the existing timber beams has to be designed. Those connections are most of the time made with glued-in rods. This paper presents a research carried out to develop a FE model which may predict the behaviour, e.g. the strength and the stiffness, of glued-in rods used for continuity joints.

PL

Obowiązujące standardy i normy koncentrują się na współczesnych połączeniach kołkowych i zazwyczaj nie zawierają zbyt wielu wytycznych dla projektantów wykorzystujących tradycyjne połączenia. Skuteczna naprawa elementów drewnianych wymaga złożonych i interdyscyplinarnych działań, uważnych badań i realizacji. W obszarze odnowy historycznych budynków inżynierowie pracują na dawnych konstrukcjach, zbudowanych ze źle zachowanych elementów drewnianych, połączonych różnymi tzw. „tradycyjnymi złączami’. Połączenia odgrywają kluczową rolę w pracy konstrukcji starych drewnianych obiektów. Konieczne jest przeprowadzenie dalszych badań w tym obszarze, aby wypracować rzetelne specyfikacje dla projektantów, protokół procedur naprawczych oraz rekomendacje dla przyszłych interwencji renowacyjnych lub wzmacniających. Zabytkowe dachy drewniane odgrywają istotną rolę z punktu widzenia historycznego i estetycznego oraz wymagają dogłębnego zrozumienia oryginalnie zastosowanych zasad i technik, w celu wybrania właściwej strategii naprawczej. Podczas renowacji belki za pomocą protezy konieczne jest zaprojektowanie ciągłego połączenia pomiędzy protezą a zdrową częścią starej belki drewnianej. Połączenia takie wykonuje się najczęściej z wykorzystaniem wklejanych prętów. Artykuł opisuje badania przeprowadzone w celu opracowania Modelu Elementów Skończonych, który będzie w stanie prognozować pracę i zachowanie, np. wytrzymałość oraz sztywność wklejanych prętów wykorzystywanych w złączach ciągłych.