降雨を考慮した積雪荷重の推定方法に関する研究

In February 2014, owing to heavy snowfall in the Kanto-Koshin region, several buildings were severely damaged. A major cause for the damage was the load on building surfaces caused by heavy snow followed by a surcharge load due to the ensuing rainfall. Countries such as the United States and Canada have established standards on snow loads, which also take into account the surcharge load due to rainfall. In contrast, Japan has not adopted such standards, and hence it is imperative to establish a method for calculating loads added by rainfall to snow loads. Therefore, in this study, experiments were conducted using artificial rainfall on roofs covered with snow to evaluate and propose a calculation method for loads added by rainfall.First, outdoor experiments as well as indoor experiments in a low-temperature experimental facility were conducted. Model roofs with different span lengths and gradients were built and loaded with natural and artificial snow. These model roofs were then treated with rainfall at constant intensity by using an artificial rainfall simulator. The increase in load was measured and several observations were made from the experiments. A smaller roof gradient and larger roof span resulted in a greater peak value of the load added by rainfall. For roofs of the same shape, the peak value of the load added by rainfall increased as the initial snow depth increased. Next, the relationship between surcharge loads due to rainfall and the span length and gradient of the roofs was quantified. The load added by the rainfall was treated as the approximate square root of the snow depth, and a coefficient a, which depends on the span length and gradient of the roof, was defined. However, valuable data were obtained from the experiments for only five types of roof geometries. To estimate the values of the coefficients a for other roof geometries, regression analysis between the coefficient a, roof gradient, and span length was conducted. Comparing the surcharge loads, which were calculated using the estimated coefficients a, with the loads calculated using the O'Rourke equation, a relatively good correspondence between both the results was confirmed.Snow loads that take rainfall into account were obtained for the given regions with corresponding values of the design snow depth. This was achieved by including the load due to rainfall, which is correlated to the snow depth, computed from the proposed formula and the estimated coefficients. In addition,