Direct stiffness method

Résumé

As one of the methods of structural analysis, the direct stiffness method, also known as the matrix stiffness method, is particularly suited for computer-automated analysis of complex structures including the statically indeterminate type. It is a matrix method that makes use of the members' stiffness relations for computing member forces and displacements in structures. The direct stiffness method is the most common implementation of the finite element method (FEM). In applying the method, the system must be modeled as a set of simpler, idealized elements interconnected at the nodes. The material stiffness properties of these elements are then, through matrix mathematics, compiled into a single matrix equation which governs the behaviour of the entire idealized structure. The structure’s unknown displacements and forces can then be determined by solving this equation. The direct stiffness method forms the basis for most commercial and free source finite element software. The dire

Source officielle

https://en.wikipedia.org/wiki/Direct_stiffness_method

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La modélisation numérique des solides est abordée à travers la méthode des éléments finis. Les aspects purement analytiques sont d'abord présentés, puis les moyens d'interpolation, d'intégration et de résolution de la mécanique sont étudiés.

L'étudiant acquiert une initiation théorique à la méthode des éléments finis qui constitue la technique la plus courante pour la résolution de problèmes elliptiques en mécanique. Il apprend à appliquer cette méthode à des cas simples et à l'exploiter pour résoudre les problèmes de la pratique.

The student will acquire the basis for the analysis of static structures and deformation of simple structural elements. The focus is given to problem-solving skills in the context of engineering design.

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Effect of Natural Weathering on Durability of Pultruded Glass Fiber-Reinforced Bridge and Building Structures

Julia De Castro San Roman Fest, Thomas Keller, Nikolaos Alexandros Theodorou, Anastasios Vassilopoulos

After 17 and 15years of use, respectively, a detailed inspection of a pedestrian bridge and a 5-story building structure composed of partly adhesively bonded pultruded glass fiber-reinforced polymer (GFRP) profiles was conducted accompanied by full-scale serviceability and destructive coupon testing on exchangeable profiles. The bridge is exposed to a harsh Alpine climate and the building to a mild plateau climate. The system and material stiffness of the bridge remained unchanged during the 17years. The material strength of the bridge, however, was significantly affected by combined freeze-thaw cycles and ultraviolet (UV) irradiation. The latter accelerated the strength degradation by uncovering the fibers (fiber blooming) and thus inducing humidity ingress into the material by wicking effects. A large majority of the small-area adhesive bonds in the bridge were intact, although a few small cracks were observed in some joints at the surface. The large-area bonds of the building did not show any damage. Based on results of the inspection of the bridge, the application of an appropriate coating on pultruded GFRP structures exposed to harsh environments is recommended. (C) 2015 American Society of Civil Engineers.

American Society of Civil Engineers2016

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In the field of timber load-bearing structures, adhesive bonding is a promising joining technique that may increase the structural stiffness and capacity of timber joints and structures. The use of ductile adhesives may furthermore allow designing ductile joints, which can compensate for the material ductility that timber lacks. To demonstrate the potential of this approach, adhesively-bonded double-lap timber joints were manufactured using a ductile acrylic adhesive and then subjected to axial tension and compression loading. The load-displacement responses were measured and compared to those of the same joint configuration for which a brittle epoxy adhesive was used. The effect of the different adhesives on the joint capacity and ductility has been studied and quantified. Strain field measurements using the Digital Image Correlation (DIC) technique and a quadratic strain interaction criterion provided a better understanding of the mechanical behavior of the two different joint types.

2018

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Ductility of adhesively bonded timber joints

Myrsini Angelidi, Thomas Keller, Anastasios Vassilopoulos

In the field of timber engineering, adhesive bonding remains a promising, though poorly developed, joining technique that may increase the structural stiffness and capacity of timber joints and structures. Selecting ductile adhesives may further allow to conceive ductile joints, which can compensate for the missing material ductility of timber. To demonstrate the potential of this approach, adhesively bonded double-lap timber joints were manufactured using a ductile acrylic adhesive and then subjected to axial tension and compression. The load–displacement responses were captured and compared to those of the same joints composed of a brittle epoxy adhesive. The effect of the different adhesives on the joint ductility has been studied and quantified.

WIT Press2017

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