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

弯曲壳结构是由厚度为2-3厘米，宽度为10-20厘米的弯曲堆叠板用螺钉固定而成，作为木结构方法具有许多优点。因为它可以以非常低的成本实现一个覆盖大面积的巨大穹顶。但从结构设计的角度看，其强度性能存在诸多不确定性。本文采用比例模型试验和数值分析方法对该结构的强度特性和变形行为进行了研究。模型实验采用长200 ~ 450cm、厚2 ~ 3mm的云杉长薄板。这些木板的两端固定在销钉支架上，其中一个支架固定在滑动基座上，以便通过测力元件测量水平力。本文研究了三种类型的结构：1)简单的木板堆叠；2)奇数层的纵向木板，但在网格点的交叉处有偶数层的交叉构件；3)用垫片填充第二种结构的间隙。模型结构用小螺栓固定在网格点上，从一层到五层结构进行检测。实验结果表明，与整体结构相比，弯曲叠合板结构在三层结构和五层结构下的刚度分别只有75%和38%。3型结构比2型结构有很大的优势，即这种薄板在没有空间填充构件的情况下会发生屈曲现象。一般采用有限元法对壳结构进行应力分析，但对这种受自重弯曲的材料制成的弯曲梁进行有序有限元分析是非常困难的。在这里，我们开发了一个新的有限元程序，用牛顿-拉普森法，考虑几何非线性效应。程序分析结果与试验结果吻合较好，如荷载-挠度曲线、挠度形状、弯矩分布等。由此可见，该技术对于螺旋弯曲叠合板结构的分析是非常有前景的。少

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