In spatial trusses, Snow load is much more important than building. As in buildings snow load is only a small proportion of the overall weight of the building, it would not affect a lot in our studies of earthquake. However in spatial trusses, snow weight will simply is twice or three times of the weight of the structure. Therefore using a proper method in studying the power of snow weight and the power of earthquake at the same time seems necessary.
The snow weight of a slope roof on its horizontal image of the slope surface is explained this way:
P5 = C5Pf
In this equation Ps and Pf are the snow weight of a slope roof and flat surface respectively. And Cs is the coefficient of slope of the roof, and as the gradient increases, the amount of snow compacted in the roof would become lessen. This happens as some snow falls of the slippery roof and also the wind blows some of it off these types of roofs. The amount of snow that decreases in a slope roof depends on how slippery it is and the temperature of the area beneath this roof.
Slope roofs with slippery surfaces (such as those which are covered in metal or have been tiled) are more likely to diminish snow.
The amount of snow weight in flat surfaces is described as below;
Pf = 0.7CcC11Pg
In this equation Pf is the snow weight in a flat surface, Pg is the snow weight on the ground, I is the importance of the building's coefficient, Ct is the thermal coefficient and Ce is the wind coefficient.
According to the different usages of spatial structures, the importance of the building's coefficient is noted to be 1/2.