Medieval Timber Roof Structures: Conceptual methods for investigation and evaluation of structural behaviour, with the horizontal thrust problem as an application

Abstract: The medieval timber roof structures hidden in the attics of many Swedish churches represent the advanced building technology of the time. They are an important cultural heritage, their being bearers of information from a period regarding which other direct sources of information are scarce. Understanding their structural action is necessary in order to be able to preserve them prop¬erly and also helps one better interpret their place in history. Timber roofs can be complex to analyse since they often possess a high degree of static inde¬terminacy, having several possible load paths. In analysing such a structure, the stiffness of its separate parts needs to be taken into account. Computa¬tional modelling by means of the finite element method (FEM) together with visualisation tools proposed for use here were found to be effective in analys¬ing their behaviour and in diagnosing damages that can occur. Many such damages can be attributed to weakness in the horizontal support of the roof structures involved. A mechanical model consisting of connected springs rep¬resenting the horizontal supportive stiffness of different parts of a building was developed. In addition, an approach that involves classifying the exten¬sion of horizontal supports for a roof structure in space was proposed. Both were used to analyse how the horizontal thrust is carried in existing buildings and to help develop new designs for horizontal support. Having access to the tools and methodologies proposed makes it possible to gain a better under¬standing of the structural behaviour of medieval roof struc¬tures, to compare different designs, to conceptualize new solutions, and facili¬tates collaboration between different professions in restoration work.

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