jabacus - Snow Drift Load Calculator

Specified Snow Load

[4.1.6.2]

S = I_s[S_s(C_bC_wC_sC_a)+S_r]

Factors

User input values:

Ss = 1

Sr = 1

Importance Factors

ULS: I_s = 1.25

SLS: I_s = 0.9

Roof slope = 0 degrees
Slope Factor

For non-slippery roof:
Slope <= 30 degrees.
C_s = 1

C_b = 0.8

Density = γ = 3 kN/m³

[Structural
Commentaries
Fig G-8]

Drift Factors & Distribution

C_a(0) = 0.67*γ h/(C_bS_s = 2.513

a) when C_a(0) < ( 0.8/C_b=1 ) : C_a(0)=0.8/C_b
b) when C_a(0) > ( 2/C_b=2.5 ): C_a(0)=2/C_b

C_a(0) = 2.5

x_d = 2h = 2 m. But 3 m ≤ x_d ≤ 9 m:

x_d = 3 m

h' = h - C_bC_wS_s/γ = 0.733m

Min dist where (C_w = 1.0) = 10*h' = 7.333 m

Obstruction effect limit = 3 S_s / γ = 1 m

Snow Load Summary

( b = 10 m ) > ( 3*S_s / γ = 1 m )

x = 0

C_w = 1

C_a(0) = 2.5

S_ULS = 1.25[1(0.811*2.5)+1] = 3.75 kPa

S_SLS = 0.9[1(0.811*2.5)+1] = 2.7 kPa

0 < x ≤ ( x_d = 3m )

C_w = 1
C_a(x) decreases linearly over 0 < x ≤ x_d
Ca(x) = 2.5 - 0.5 * x (with x in meters)

x = x_d = 3m

C_w = 1

C_a(x_d) = 1

S_ULS = 1.25[1(0.811*1)+1] = 2.25 kPa

S_ULS = 0.9[1(0.811*1)+1] = 1.62 kPa

x > ( x_d = 3m )

C_w = 1.0

C_a(x) = 1

Snow drift loading - adjacent to roof obstructions

Climatic Data

Factors

Roof Projection

Roof geometry

Specified Snow Load

Factors

Drift Factors & Distribution

C_a(0) = 2.5

x_d = 3 m

Snow Load Summary

x = 0

S_ULS = 1.25[1(0.811*2.5)+1] = 3.75 kPa

S_SLS = 0.9[1(0.811*2.5)+1] = 2.7 kPa

0 < x ≤ ( x_d = 3m )

x = x_d = 3m

S_ULS = 1.25[1(0.811*1)+1] = 2.25 kPa

S_ULS = 0.9[1(0.811*1)+1] = 1.62 kPa

x > ( x_d = 3m )

S_ULS = 1.25[1(0.81.01*1)+1] = 2.25 kPa

S_SLS = 0.9[1(0.81.01*1)+1] = 1.62 kPa

Snow drift loading - adjacent to roof obstructions

Climatic Data

Factors

Roof Projection

Roof geometry

Specified Snow Load

Factors

Drift Factors & Distribution

Ca(0) = 2.5

xd = 3 m

Snow Load Summary

x = 0

SULS = 1.25[1(0.8*1*1*2.5)+1] = 3.75 kPa

SSLS = 0.9[1(0.8*1*1*2.5)+1] = 2.7 kPa

0 < x ≤ ( xd = 3m )

x = xd = 3m

SULS = 1.25[1(0.8*1*1*1)+1] = 2.25 kPa

SULS = 0.9[1(0.8*1*1*1)+1] = 1.62 kPa

x > ( xd = 3m )

SULS = 1.25[1(0.8*1.0*1*1)+1] = 2.25 kPa

SSLS = 0.9[1(0.8*1.0*1*1)+1] = 1.62 kPa

C_a(0) = 2.5

x_d = 3 m

S_ULS = 1.25[1(0.811*2.5)+1] = 3.75 kPa

S_SLS = 0.9[1(0.811*2.5)+1] = 2.7 kPa

0 < x ≤ ( x_d = 3m )

x = x_d = 3m

S_ULS = 1.25[1(0.811*1)+1] = 2.25 kPa

S_ULS = 0.9[1(0.811*1)+1] = 1.62 kPa

x > ( x_d = 3m )

S_ULS = 1.25[1(0.81.01*1)+1] = 2.25 kPa

S_SLS = 0.9[1(0.81.01*1)+1] = 1.62 kPa