Structural Mechanics Modelling and Analysis of Frames and Trusses By Karl Gunnar Olsson And Ola Dahlblom
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Structural Mechanics Modelling and Analysis of Frames and Trusses By Karl Gunnar Olsson And Ola Dahlblom


The autumn sun shines on Sunnibergbrücke at Klosters in the canton of Graubünden in south-western Switzerland. On the cover picture one can sense how the bridge elegantly migrates through the landscape. The steel and concrete structure and the architecture merge into one of the most elegant buildings of our time. The engineer who designed the bridge is named Christian Menn. It is late in October 2009, and a group of Swedish students sketch, photograph and enthusiastically discuss the shape and the structural behaviour of the bridge. In a week they will start a course in structural mechanics. Structural mechanics is the branch of physics that describes how different materials, which have been shaped and joined together to structures, carry their loads. Knowledge on the modes of action of these structures can be used in different contexts and for different purposes. The Roman architect and engineer Vitruvius, who lived during the first century BC summarises in the work De architectura libri decem (‘Ten books on architecture’) the art of building with the three classical notions of firmitas, utilitas and venustas (strength, functionality and beauty). Engineering of our time has basically the same goal. It is about utilising the knowledge and practices of our time in a creative process where sustainable and efficient, functional and expressive buildings are designed. At an early design stage a structural engineer needs to be trained to see how to efficiently use material and shape to provide the construction with stability, stiffness and strength. Using simple models, structural behaviour can be evaluated and cross-section sizes estimated. As the design develops the need for precision of the analyses increases.

In all this, the ability to formulate computational models and to carry out simulations is of crucial importance. A useful computational model should be simple enough to be easily manageable and, simultaneously, sufficiently complex to provide an adequate accuracy. In recent years, the finite element method has become the dominant method for formulating computational models and conducting analyses. The FE method is based on expressing forces and deformations as discrete entities in a chosen and representative set of degrees of freedom. Between the degrees of freedom simple bodies (elements) are placed and together they constitute the structure to be modelled. Each element may describe a unique mode of action and can be given a specific geometry. In all this, FEM provides opportunities for both accurate analyses of structures with complex geometry and material behaviour, and for quick estimates in early design stages. Here, we present a new textbook in structural mechanics, dealing with the modelling and analysis of trusses and frames. The textbook is based on the finite element method. Gradually, an understanding of basic elements of structural mechanics – springs, bars, beams, foundations and so on is built up. Methods for assembling them into complex load-bearingstructures are presented, and tools for analysis and simulation are provided. The book has been limited to treating trusses and frames in two and three dimensions.

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