Basic study on the strength estimation of curved stacked plank structures with screw fixation

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The curving shell structures, which are obtained by fixing the curved stacked planks sized 2-3 cm thickness and 10-20 cm width with screws, have many advantages as a timber structuring method. Because it can realize a huge dome that covers a large area by very low cost. Though, there are many uncertainties in its strength performances from the view points of the structural design. In this research, the strength nature and deformation behavior of this structure were studied using scale model experiments and a numerical analysis method.In the model experiments, long thin planks of spruce sized 200-450cm long and 2-3 mm thickness were used. Both ends of these planks were fixed to pin supports, and one support was hold on a sliding base to enable the measurement of the horizontal force by a load-cell. Three types of structure were examined here : 1) simple stacking of planks, 2) longitudinal planks with odd number layers, but crossing members at grid points with even number layers, 3) fill … More ed the gap of the second structure by spacers. Model structures were fixed at the grid points with small bolts, and from one to five layer structures were examined. From this experiments, it was proved that the curved stacked plank structure shows only 75% and 38% rigidity, for three layer structure and five layer structure, respectively, compared with the structure as an unity. The structure type 3 has much advantage to type 2 structure, which means that there occurs buckling phenomenon without space filling members for such a thin planks.It is common to use the Finite Element Method (FEM) to the stress analysis of the shell structure, but it is very difficult to realize the loading analysis on the curved beams made of such a material that is bent by the self-weight by an ordinal FEM. Here, we developed a new FEM program, with Newton-Lapson's method, that takes account the geometrical non-linear effects. Analysis by this program showed good agreement with experimental results such as the load-deflection curve, the deflection shape and bending moment distribution. Thus, it became clear that this technique was very promising for the analysis of the screwed curved stacked-planks structure. Less