What ASCE 7 section covers sign and billboard wind loads?

ASCE 7-16 and ASCE 7-22 Section 29.3 covers wind loads on solid freestanding walls and solid signs. This section provides force coefficients (Cf) from Figure 29.3-1 for calculating design wind forces on signs, billboards, and freestanding walls.

What is the design wind force formula for signs?

The design wind force for signs is F = qh × G × Cf × As, where qh is velocity pressure at height h, G is the gust-effect factor (typically 0.85 for rigid signs), Cf is the force coefficient from Figure 29.3-1, and As is the gross area of the sign.

What is the difference between Case A, B, and C for sign wind loads?

Case A applies uniform pressure across the sign face. Case B applies the same total force but with eccentricity (offset 0.2B from center) to account for torsion. Case C applies only when B/s >= 2 and creates two zones with different force coefficients (Cf = 2.25 for zone 0-s and Cf = 1.5 for zone s-2s).

What is considered a solid sign vs open sign per ASCE 7?

A sign is considered solid if openings comprise less than 30% of the gross area. For signs with openings less than 30%, a porosity reduction factor can be applied: Factor = 1 - (1-epsilon)^1.5, where epsilon is the ratio of solid area to gross area. Signs with 30% or more openings use different provisions.

How does clearance ratio affect sign wind loads?

The clearance ratio (s/h) where s is the sign height and h is the clearance from ground to bottom of sign, affects the force coefficient Cf. Lower clearance ratios (sign closer to ground) generally result in lower force coefficients due to ground effect reducing wind exposure.

Sign & Billboard Wind Load Guide | ASCE 7-16 & 7-22

🚩 Introduction to Sign Wind Loads

Signs, billboards, and freestanding walls are subject to significant wind forces due to their large surface areas and elevated positions. ASCE 7 provides specific provisions in Section 29.3 for calculating design wind loads on these structures.

This guide covers wind load calculations for both solid signs (less than 30% open) and considerations for open/porous signs, explaining the force coefficient (Cf) determination, the three load cases (A, B, and C), and step-by-step calculation procedures per ASCE 7-16 and ASCE 7-22.

ⓘ Sign Types Covered

Section 29.3 applies to freestanding signs (ground signs, monument signs, pole signs), billboards, and solid freestanding walls. For wall-attached signs with specific conditions, different provisions may apply.

🔢 Design Wind Force Formula

The design wind force for solid freestanding walls and solid signs per ASCE 7 is calculated using:

F = q_h × G × C_f × A_s

F = design wind force (lb)
q_h = velocity pressure at height h (psf)
G = gust-effect factor (0.85 for rigid structures)
C_f = force coefficient from Figure 29.3-1
A_s = gross area of the sign (ft²)

Velocity Pressure (q_h)

The velocity pressure is calculated at the centroid height (h) of the sign:

q_h = 0.00256 × K_h × K_zt × K_d × K_e × V²

K_h = velocity pressure exposure coefficient at height h
K_zt = topographic factor
K_d = wind directionality factor (0.85 for signs)
K_e = ground elevation factor
V = basic wind speed (mph)

ⓘ ASCE 7-22 Change

In ASCE 7-22, the directionality factor (K_d) was removed from the velocity pressure equation and incorporated directly into individual force and pressure equations. The net effect is the same, but the calculation sequence differs slightly from ASCE 7-16.

📈 Solid vs. Open Signs

ASCE 7 distinguishes between solid and open signs based on the percentage of openings:

Sign Type	Openings	ASCE 7 Treatment
Solid Sign	< 30% of gross area	Use Section 29.3 with porosity reduction factor permitted
Open Sign	≥ 30% of gross area	Use visual (see-through) porosity calculation

Porosity Reduction Factor for Solid Signs

For solid signs with some openings (less than 30%), the force coefficient may be multiplied by a porosity reduction factor:

Reduction Factor = 1 - (1 - ε)^1.5

ε = ratio of solid area to gross area (solidity ratio)

Example: For a sign that is 75% solid (25% open):
Factor = 1 - (1 - 0.75)^1.5 = 1 - 0.125 = 0.875
This means the wind force is 87.5% of a fully solid sign.

🗺 Force Coefficient (C_f) from Figure 29.3-1

The force coefficient C_f is determined from ASCE 7 Figure 29.3-1 based on two key ratios:

B/s = ratio of sign width (B) to sign height (s)
s/h = ratio of sign height (s) to clearance from ground (h)

Figure 29.3-1 provides C_f values for up to three different load cases depending on the sign geometry:

Sign Geometry Parameters

Parameter	Definition	Impact on C_f
B	Horizontal dimension (width) of sign	Wider signs require Case C analysis
s	Vertical dimension (height) of sign	Used in aspect ratio calculations
h	Height from ground to bottom of sign	Higher clearance = higher C_f

🎯 Load Cases A, B, and C

ASCE 7 Figure 29.3-1 defines three load cases that may need to be considered depending on sign geometry:

Case A Uniform Load

Applies: All signs (always required)

Load Pattern: Uniform pressure across entire sign face

Force Location: Applied at geometric center of sign

Purpose: Maximum total force on sign and foundation

Case B Eccentric Load

Applies: All signs (always required)

Load Pattern: Same total force as Case A, but offset from center

Eccentricity: D_x = 0.2 × B (20% of sign width)

Purpose: Maximum torsion on support structure

Case C Two-Zone Load

Applies: Only when B/s ≥ 2

Load Pattern: Two zones with different C_f values

Zone 1 (0 to s): C_f = 2.25

Zone 2 (s to 2s): C_f = 1.50

Purpose: Maximum localized pressure on wide signs

⚠ All Applicable Cases Must Be Checked

The sign and its support structure must be designed for the maximum effects from all applicable load cases. For most signs, both Case A and Case B are required. For wide signs (B/s ≥ 2), Case C must also be considered.

📐 Typical Force Coefficient Values

The following table provides representative C_f values from Figure 29.3-1 for common sign configurations:

B/s Ratio	s/h ≤ 0.8	s/h = 1	s/h ≥ 2
≤ 1	1.80	1.70	1.55
2	1.70	1.65	1.50
5	1.60	1.55	1.40
≥ 10	1.55	1.50	1.35

Note: These are approximate values for Case A. Always refer to ASCE 7 Figure 29.3-1 for exact coefficients. Values vary based on interpolation between listed ratios.

🛠 Support Column Wind Loads

In addition to the sign face, wind loads on support columns (poles, posts) must be calculated separately. ASCE 7 treats cylindrical supports using provisions similar to chimneys and other structures:

Cylindrical Support Force Coefficient

For round pole supports, the force coefficient depends on:

Surface roughness - Smooth vs. rough (moderately smooth for most steel poles)
Reynolds number effects - Related to D×q_h^0.5
Aspect ratio - h/D ratio of the pole

Typical C_f values for cylindrical supports range from 0.5 to 1.2 depending on conditions. Square or rectangular supports use higher coefficients (typically 1.3 to 2.0).

🏭 Wall-Attached Signs

Signs attached to building walls have special provisions:

Gap Condition: When gap between sign and wall ≤ 3 ft AND sign edge is ≥ 3 ft from wall free edges
Internal Pressure: GC_pi = 0 (no internal pressure consideration)
Design Pressure: Use wall C&C pressures from Chapter 30 for the sign location zone

ⓘ Wall-Attached vs. Freestanding

Wall-attached signs that meet the gap and edge criteria are designed using building wall pressures, which are typically lower than freestanding sign forces. Signs that don't meet these criteria should be designed as freestanding structures.

📝 Example Calculation

The following example demonstrates a billboard wind load calculation:

Given Parameters:

Location: Tulsa, Oklahoma
Design wind speed (V): 115 mph (Risk Category II)
Exposure Category: C
Sign dimensions: 14 ft wide (B) × 48 ft high panel (s)
Height to bottom of sign (h): 20 ft
Solid sign (no openings)

Step-by-Step Calculation:

Calculate geometric ratios:
B/s = 48/14 = 3.43
s/h = 14/20 = 0.70
Determine height to centroid:
h_centroid = 20 + 14/2 = 27 ft
Calculate velocity pressure (q_h):
K_h at 27 ft (Exposure C) = 0.94
K_zt = 1.0 (flat terrain)
K_d = 0.85 (signs)
K_e = 1.0
q_h = 0.00256 × 0.94 × 1.0 × 0.85 × 1.0 × 115² = 27.0 psf
Determine C_f from Figure 29.3-1:
For B/s = 3.43 and s/h = 0.70, interpolate: C_f ≈ 1.63
Calculate sign area:
A_s = 14 × 48 = 672 ft²
Calculate design wind force (Case A):
F = 27.0 × 0.85 × 1.63 × 672 = 25,140 lb
Check Case C (since B/s ≥ 2):
Zone 1 force (C_f = 2.25): F₁ = 27.0 × 0.85 × 2.25 × (14 × 14) = 10,120 lb
Zone 2 force (C_f = 1.50): F₂ = 27.0 × 0.85 × 1.50 × (14 × 34) = 16,400 lb

ⓘ Design Considerations

The sign structure must be designed for Case A (maximum total force of 25,140 lb), Case B (same force with 9.6 ft eccentricity for torsion), and Case C zone forces for localized member design. Support columns and foundation must resist overturning moment from the applied force at the centroid height.

🔄 ASCE 7-16 vs. ASCE 7-22 for Signs

Feature	ASCE 7-16	ASCE 7-22
Section Reference	29.3	29.3
Force Coefficient Figure	29.3-1	29.3-1
K_d Location	In velocity pressure equation	In force equation
Porosity Reduction	Note 2 of Figure 29.3-1	Note 2 of Figure 29.3-1
Load Cases A, B, C	Required per Figure 29.3-1	Required per Figure 29.3-1

ⓘ Minimal Changes for Signs

Unlike some other provisions, sign wind load calculations are largely unchanged between ASCE 7-16 and ASCE 7-22. The main difference is the repositioning of K_d from the velocity pressure equation to individual force equations, but the final results are identical.

🛠 Design Considerations

Foundation Design

Overturning moment: M = F × (h + s/2)
Soil bearing capacity must resist foundation reactions
Anchor bolts must resist combined shear and tension

Support Structure

Bending moment in columns from wind force
Torsion from Case B eccentric loading
Combined stresses from dead load + wind

Connection Design

Sign-to-structure connections must transfer wind forces
Base plate connections sized for overturning moment
Fatigue considerations for repeated wind loading

⚠ Professional Engineering Required

Sign structures, especially billboards and large freestanding signs, typically require design by a licensed Professional Engineer. Many jurisdictions require PE-stamped drawings and calculations for sign permits.

Calculate Your Sign Wind Loads

Use our professional wind load calculator to determine design forces for your sign or billboard per ASCE 7-16 or ASCE 7-22.

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🔗 Resources and References

ASCE 7 Hazard Tool - Official tool for site-specific wind speeds
ASCE/SEI 7-22 Standard - Official ASCE 7-22 publication
ICC Digital Codes - International Building Code reference

Sign & Billboard Wind Load Calculations