Horisontalstabilisering i småhus - Råspont som stabiliserande system i tak

Each year, approximately 10 000 single-family houses are built in Sweden, a majority of which are timber-framed. Even larger buildings are more commonly being designed with timber structural systems as wood is considered having a lesser impact on the environment compared to steel and concrete. In most single-family houses, prefabricated timber roof trusses are used in combination with tongue-and-groove planking as the load-carrying roof structure. The planking is partially used in order to distribute the vertical loads but also in order to stabilize the structure against horizontal loads. Even though tongue-and-groove planking has been used for decades in single-family houses, there is currently no established method, in Sweden, in order to calculate its in-plane load-carrying capacity. Generally it is currently not required to check the horizontal stability of single-family houses, however, in the early 2000s several collapses in timber-structures occurred throughout Europe due to insufficient horizontal stability. Thus, there is a possibility that the requirements in Eurocode might be tightened. Therefore, there is an interest in being able to confirm the adequacy of the lateral stability even in small houses. The purpose of this thesis is therefore to investigate the accuracy of theoretical calculations by comparing theoretical results with experimental results. The objective is to conclude whether or not a design-equation is applicable in structural engineering calculations. In the early stages of the literature review, a canadian equation was found which uses the force-couples in every pair of nails to calculate the structure's in-plane shear-capacity. In this thesis, a literature review, tests and calculations were carried out. The literature study was conducted in order to gain knowledge regarding the in-plane shear capacity of timber structures. The tests comprised a total of 13 specimens with three different assemblies. The specimens were 2,4 x 2,5 m elements consisting of tongue-and-groove sheets with pins nailed to timber studs with a cc of 1200 mm. Before the tests were carried out, theoretical calculations of the specimen's racking strength were executed. Finally, an example of how the theoretical equation could be applied in a typical 1,5-storey single-family house was conducted with the intention to investigate whether or not the results were sufficient to handle the lateral stability. The results from the tests showed that in the specimen where the pins were removed and individual planks were used, the equation gave an accurate estimation of the in-plane shear capacity whereas the specimen with pins had a capacity more than twice that of the calculated value. Furthermore, the stiffness in the specimens with pins were significantly higher than in the specimen without. It was also concluded that the jointing method in between the sheets, friction and the moisture content did not appear to affect the strength. In the example, the design-equation was applied to a 1,5-storey single-family house exposed to large snow- and wind loads and it was concluded that the tongue-and-groove planking provided sufficient lateral stability without considering the extra capacity from the pins.

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