Lateral & Axial Loads

The wind force to a given post will be based on:

• The Wind Pressure, q_w
• The Velocity Pressure Exposure Coefficient, K_z
• The Topographic Factor, K_zt
• The Elevation Factor, K_e
• The Inverted Fence Opening Reduction Factor for wind loading, R_1w
• The Force Height Adjustment Factor for wind loading, F_hw
• The Wind Force Coefficient, C_fw
• The height of the fencing material, s (ft)
• The spacing of the fence posts, L (ft)
• The Solidity Ratio, ε
• The Dead Load of the fencing material, D_m (psf)
• For open fencing, you will also need:
  • The diameter or width of the expected post size, Ø_p (in) – this may change after post selection.  For solid or mostly solid fencing, Ø_p = 0
  • The diameter or width of the top rail, Ø_r (in) – if not applicable, Ø_r = 0.  For solid or mostly solid fencing, Ø_r = 0
  • The diameter or width of the mid rail, Ø_m (in) – if not applicable, Ø_m = 0.  For solid or mostly solid fencing, Ø_m = 0
  • Bottom rails can be ignored as they are too close to the ground to affect post sizing.
• The wind area tributary to the post, A_w = ε s L
  • For open fencing, add (Ø_p /12) × h + (Ø_r / 12) × 2 × L + (Ø_m / 12) × L to account for the exposed post and rails if applicable.

The minimum wind force in pounds (lbs) to the post, f_min = (0.6) 16.0 A_w

The calculated wind force, f_w = q_w K_z K_zt K_e R_1w F_hw C_fw A_w

If the fence is expected to act as a railing, the minimum guard rail forces would be:

• f_d = 50 plf distributed load x post spacing, L x 5′ force application height ÷ ½h

• f_c = 200 lb concentrated load x 5′ force application height ÷ ½h     (This load case only controls if the Post Spacing, L is less than 4′)

• If the fence / guardrail height is less than 5′, then the height, H would be used as the force application height for both f_d & f_c.

The maximum wind force, f_w‘ = the maximum value of f_min, f_w, f_d or f_c

As the axial load on the post affects the bending strength, the following is also needed:

• The Axial Load supported by the post, p_w = D_m s L
• 5 × the p_w value for a stability check

For wind on ice forces, additional variables are required.

• The Wind on Ice Pressure, q_i
• The Inverted Fence Opening Reduction Factor for Wind on Ice loading, R_1i
• The Force Height Adjustment Factor for wind on ice loading, F_hi
• The Wind on Ice Force Coefficient, C_fi
• The Iced Solidity Ratio, ε’
• The Dead Load of Ice buildup on the fencing, D_i (psf)
• The wind area tributary to the post in the iced condition, A_i = ε’ s L

The Wind on Ice force, f_i (lbs) applied to the post is:

f_i = q_i K_z K_zt K_e R_1i F_hi C_fi A_i

As the axial load on the post affects the bending strength, the following is also needed:

• The Axial Load supported by the post, p_i = (D_m + D_i) s L
• 5 × the p_i value for a stability check

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Worksheets

Open Fencing (e.g. chain link) – Wind Only – No Ice Loading

Solid or Mostly Solid Fencing – Wind Only – No Ice Loading

Fencing – All Types – Wind and Ice Loading

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