Ice Loading Calculations

Variables needed:

Nominal Ice Thickness, t

Fence Height, h                 ASCE 7 Eq. 10.4-4 uses z for height above ground – f_z formula below altered to estimate the average value across the height of the fence.

Height of fencing materials, s       (h minus any gap at the bottom of the fence)

Topographic Factor, K_zt

Importance Factor for Ice, I_i         (not used in ASCE 7-22, so I_i set to 1.0 in that case)

Ice Thickness Modifier, m_t           (corrects for formula differences between ASCE 7 versions)

Height Factor, f_z per Eq. 10.4-4 (½ h substituted for z)                   

f_z = (½ h / 33)^0.10

Design Ice Thickness for Freezing Rain, t_d per Eq. 10.4-5                  

t_d = m_t t I_i f_z K_zt ^0.35

For K_zt = 1.0 (flat ground), Eq. 10.4-5 simplifies to t_d = m_t t I_i f_z

The Density of Ice, I_d = 56 lbs / ft³ per ASCE 7 §10.4.1 (minimum value)

For a solid fence:

Iced Area, A_i = 0.8 s L     (0.8 is reduction factor for vertical plates per §10.4.1)

The Volume of Ice, V_i = π t_d A_i                per Eq. 10.4-1

The Weight of Ice, D_i = V_i I_d

For open fencing, the ice solidity ratio, ε’ is based on adding the design ice thickness, t_d to each free edge of the fencing members which increases the wind area. If the iced solidity ratio, ε’ exceeds 0.7, the fence is then considered to be a solid or mostly solid fence.

The cross sectional area of ice on each member is based on the “diameter of the cylinder circumscribing an object”, D_c. D_c for a variety of cross sections is shown below per ASCE 7, Figure 10-1.

The cross-sectional area of Ice per Eq. 10.4-1 is A_i = π t_d (D_c + t_d)

The volume of ice on a given member, such as a tube picket on an architectural fence would be:

V_i = A_i x the length of the member in feet.

See above for determining the weight of the ice.