Resolution of Collapse Mechanism of Timber Space Frames Subjected to Excessive Snow Load and Practical Formulation to Predict their Critical Performance.

1.通过对历年大雪季节木结构房屋破坏情况的调查，发现木结构房屋的整体倒塌主要是由于木结构的老化和雪荷载过大造成的。此外，调查问卷的结果显示，由于人们生活方式的改变，人们的房屋因缺乏人力、设备和清扫屋顶积雪的智慧而容易承受过大的积雪负荷。通过对日本雪松榫节点简支柱各种屈曲试验数据的分析，建立了预测房屋柱屈曲荷载的公式。对于简支细长柱，屈曲荷载可用欧拉方程估算;对于大柱，屈曲荷载可用修正的约翰逊方程估算.针对典型的雪区木结构房屋框架模型，通过参数分析研究了墙体体积及其布置方式对屈曲荷载及相应倒塌模式的影响，结果表明，导致其完全倒塌的条件仅限于承重墙少或墙体几乎老化的裸露骨架.通过对一典型日式屋架的竖向荷载试验及有限元分析，阐明了屋架的破坏形式既可能是梁的弯曲断裂，也可能是梁节点的拉伸断裂.最后，在总结上述研究成果的基础上，提出了预测木结构房屋在屋顶积雪荷载作用下极限承载力的原则和框架。

1. Based on the survey of damages of wooden buildings in past seasons of heavy snow, it was found that the total collapse of such buildings occurred when they were made of decrepit timber-frames and also when they suffered excessive snow load. In addition, answers to questionnaires in this study showed that the recent change in our lifestyles was liable to result to excessive snow loads to our houses due to the lack of human power, equipments, and wisdoms for the removal of snow from the roofs.2. An equation to predict the buckling load of columns in houses was formulated through the data analysis of various buckling tests of Japanese cedar simple columns with tenon joints. The buckling load can be estimated by the Euler equation for slender columns with simple supports and by the modified Johnson equation for large ones.3. For the typical frame models of wooden houses in snowy regions, the parametric analytical study to examine the effects of wall volume and their arrangements on the buckling loads or their relevant collapse modes showed that the condition that causes their total collapse was restricted to some bare-like skeletons such as those with little bearing walls or with almost decrepit ones.4. The vertical loading test of a typical Japanese-style roof truss and its relevant finite element analysis clarified that the roof truss will collapse either by the bending break of its beam or by the tensile break of a joint of the beam.5. Finally, the principle and the framework to predict the ultimate capability of timber frame houses subjected to an excessive roof snow load are proposed by summing up the above important results.