Zur Berechnung von Holzschalen in Brettrippenbauweise mit elastischem Verbundquerschnitt

摘要

The design of timber rip shells confronts the engineer with major uncertainties during the planning process. The consideration of the elastic compound cross section during structural analysis of curved members by means of conventional calculation methods is possible only in a restricted manner. The shear-analogy provides a seemingly useful method for calculating these structures. However it is only an approximation, particularly with regard to cross sections with high flexibility in terms of shear stress. This thesis treats the limitations of applying of the shearanalogy with regard to the calculation of straight and curved members with elastic compound cross section. The bending of timber lamellas generates initial bending stress. Due to the rheological behaviour of wood and the associated process of plastification within the microstructure of wood, the stress becomes partially reduced as a function of time (stress relaxation). Prior work provides contradictory information about the duration and intensity of this reduction. To shed light on these uncertainties, appropriate experiments have been conducted. To join timber lamellas to a multi-layered cross section, mechanical fasteners like screws, nails and bolts are used. The knowledge of the physical properties, like rigidity and resistance, are of significant importance for the verification of the ultimate limit states. Tests conducted in the past in order to evaluate theoretical models and to determine empirical values refer generally to connections, which differ clearly from the multi-layered connection treated here concerning the deformation and failure mechanisms. Experiments carried out provide estimation in how far the existing values can be applied to structural analysis of the present case. The theoretical model according to Johansen was adapted in an appropriate manner. The aim of the work presented here is to contribute to the clarification of several problems related to the design of spatial timber structures with elastic compound cross section. The results provide further confidence to engineers for planning and realising these challenging lightweight structures.