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Snow load

The calculations are performed in accordance with the standard EN 1991-1-3. These procedures are included:

Snow load

The snow load on the roof is calculated using formula (5.1):

The exposure coefficient C_e is obtained according to the selected topography. The values are in accordance with the table 5.1 of EN 1991-1-3:

Mono-pitched roofs

The shape coefficient μ₁ in accordance with figure 5.1 of EN 1991-1-3 is used for mono-pitched roofs. The value of this coefficient depends on the roof pitch:

Shape coefficients μ₁ and μ₂

The value of the coefficient μ₁ is equal to 0.8 if the sliding of the snow is prevented (snow fences etc.).

Duo-pitched roofs

The shape coefficient μ₁ in accordance with figure 5.1 of EN 1991-1-3 is used for duo-pitched roofs. The figure showing the dependency of the coefficient value and the roof pitch is shown in the chapter "Mono-pitched roofs". The value of the coefficient μ₁ is equal to 0.8 if the sliding of the snow is prevented (snow fences etc.). These three load cases are created for duo-pitched roof in accordance with chapter 5.3.3:

Load cases for duo-pitched roofs

Multi-span roofs

The shape coefficients μ₁ and μ₂ in accordance with figure 5.1 of EN 1991-1-3 is used for multi-span roofs. The figure showing the dependency of the coefficients values and the roof pitch is shown in the chapter "Mono-pitched roofs". The value of the coefficient μ₁ is equal to 0.8 if the sliding of the snow is prevented (snow fences etc.). These load cases for undrifted and drifted snow are created in accordance with chapter 5.4:

Load cases for multi-span roofs

Cylindrical roofs

The shape coefficient μ₃ in accordance with figure 5.3.5(1) of EN 1991-1-3 is used for cylindrical roofs. Its value is depending on ratio h/b, where h is the height of cylindrical roof and b is the roof span. The coefficient values are shown in the following figure:

Coefficient μ₃

The snow load is considered in the parts where the roof pitch is smaller than 60° according to the chapter 5.3.5. Following load cases are considered:

Load cases for cylindrical roofs

Following load case based on the standards CSN/STN 73 0035 is considered additionally for Czech and Slovak nation annexes :

Drifted snow in accordance with Czech and Slovak national annex

This load case is considered under these circumstances:

• This scheme will be considered for all cylindrical roofs with ratio h/b greater than 1/8.
• This scheme will be considered for all cylindrical roofs in snow areas IV and V.

Roofs abutting and close to taller construction works

The shape coefficients for these roofs are calculated according to the chapter 5.3.6 of EN 1991-1-3. These load cases are considered:

Load cases for abutting roofs

The shape coefficients μ₁ and μ₂ are calculated using following formulas:

The value of the coefficient μ_s is equal to 0 for α ≤ 15°. The following formula is used for α > 15°:

The coefficient μ_w is calculated using following formula:

The drift length l_s is calculated using formula

The drift length l_s is limited by the interval <5m;15m>. The shape coefficient is calculated using lineat interpolation between μ₁ and μ₂ for buildings where l_s is greater than span of lower roof.

Drifting at projections and obstructions

The following loading figure is created in accordance with the chapter 6.2 of EN 1991-1-3 for the roofs with obstructions:

Loading figure for obstructions

The coefficients μ₁ and μ₂ are calculated using formula (6.1):

Snow overhanging the edge of a roof

Snow overhanging the edge of a roof is calculated in accordance with chapter 6.3. Following formula is used:

The coefficient k is calculated using formula:

But following expression has to be fulfilled:

Snow load on snowguards and other obstacles

Snow load on snowguards and other obstacles is calculated according to the chapter 6.4 of EN 1991-1-3. Following formula is used: