EN 1991-1-4 Wind Load Guide — Eurocode Provisions

Complete reference guide to wind load determination for structural design per EN 1991-1-4:2005 (Eurocode 1: Actions on Structures — Part 1-4: Wind Actions), including amendments A1:2010 and CEN Corrigenda. Covers the full wind load procedure from basic wind velocity through peak velocity pressure, terrain categories (0–IV), external pressure coefficients cpe, internal pressure coefficients cpi, the structural factor cscd, and a worked example for a steel-framed office building in Central Europe.

Related pages: UK Wind Load | EN 1993 Steel Design | European Wind Load | Wind Load Calculator

EN 1991-1-4 Wind Load Framework

Code Reference: EN 1991-1-4:2005 + A1:2010, Sections 3-8

The Eurocode wind load procedure determines peak velocity pressure qp(z) and then applies pressure coefficients to obtain design wind pressures. The general procedure:

[ we = q_p(z_e) \times c{pe} \quad \text{(external pressure on surfaces)} ] [ wi = q_p(z_i) \times c{pi} \quad \text{(internal pressure)} ] [ Fw = c_s c_d \times \sum{surfaces} we \times A{ref} \quad \text{(overall wind force)} ]

Where:

• qp(z) = peak velocity pressure at height z (Clause 4.5)
• cpe = external pressure coefficient (Section 7)
• cpi = internal pressure coefficient (Section 7.2.9)
• cscd = structural factor (Section 6), accounting for size and dynamic effects

Step 1 — Basic Wind Velocity vb (Clause 4.2)

The fundamental basic wind velocity is:

[ vb = c{dir} \times c*{season} \times v*{b,0} ]

Where:

• vb,0 = fundamental value of the basic wind velocity (10-min mean at 10 m height in open country terrain — Terrain Category II), with annual probability of exceedance p = 0.02 (50-year return)
• cdir = directional factor (recommended value = 1.0, may be reduced per site-specific National Annex)
• cseason = season factor (recommended value = 1.0, for temporary structures may be reduced)

Selected European Cities — vb,0 Values

The National Annex for each country provides the definitive vb,0 map. The values above are typical for inland locations near the named cities. Coastal and high-altitude locations typically have higher vb,0 values. Always consult the National Annex for the project country.

Step 2 — Terrain Categories and Roughness (Clause 4.3, Annex A)

EN 1991-1-4 Terrain Categories

Terrain Factor kr and Roughness Factor cr(z) (Clauses 4.3.2–4.3.3)

The terrain factor:

[ kr = 0.19 \times \left(\frac{z_0}{z{0,II}}\right)^{0.07} ]

Where z0,II = 0.05 m (reference roughness for Terrain Category II).

The roughness factor cr(z) for z >= zmin:

[ c_r(z) = k_r \times \ln\left(\frac{z}{z_0}\right) ]

For z < zmin, cr(z) = cr(zmin).

cr(z) Values for Selected Heights — All Terrain Categories

For z < zmin: use cr(zmin). For Category II at 10 m, cr ≈ 1.0 (reference condition).

Step 3 — Peak Velocity Pressure qp(z) (Clause 4.5)

The peak velocity pressure combines the mean wind profile and turbulence:

[ q_p(z) = [1 + 7 \times I_v(z)] \times \frac{1}{2} \times \rho \times v_m^2(z) ]

Or expressed in terms of the basic velocity pressure qb:

[ q_p(z) = c_e(z) \times q_b ]

Where:

• qb = 0.5 x rho x vb^2 = basic velocity pressure
• rho = 1.25 kg/m^3 (air density, recommended value — check National Annex)
• Iv(z) = turbulence intensity = kI / [c0(z) x ln(z/z0)]
• kI = turbulence factor (recommended value = 1.0)
• c0(z) = orography factor (generally 1.0 except for hills/cliffs per Clause 4.3.3)
• vm(z) = cr(z) x c0(z) x vb = mean wind velocity
• ce(z) = exposure factor, given in Figure 4.2 or calculated

Exposure Factor ce(z) — Terrain Category II, c0 = 1.0, kI = 1.0

For other terrain categories, ce(z) is obtained from EN 1991-1-4 Figure 4.2 or calculated explicitly using the full equation of Clause 4.5.

Step 4 — External Pressure Coefficients cpe (Section 7)

Vertical Walls of Rectangular Plan Buildings (Table 7.1)

Pressure coefficients on the windward wall depend on the ratio h/d, where h = building height and d = depth parallel to wind:

Linear interpolation for intermediate h/d values is permitted.

Flat Roofs (Table 7.2)

For flat roofs with parapet height hp/h < 0.05 (or no parapet):

For roofs with parapets (hp/h > 0.025), the cpe values in zones F, G, H may be reduced per Table 7.2 note.

Key point: Zone dimensions depend on e = min(b, 2h), where b = crosswind dimension. For a building 40 m wide x 30 m deep and 15 m high: e = min(40, 30) = 30 m. Zone F = e/10 x e/10 corner squares, Zone G = e/10 wide edge strip, Zone H = interior.

Step 5 — Internal Pressure Coefficient cpi (Clause 7.2.9)

The internal pressure coefficient depends on the distribution and size of openings:

For a typical enclosed office building with uniformly distributed windows and doors: cpi = +0.2 (internal pressure) and cpi = -0.3 (internal suction). Both signs must be checked — the worst case is taken for each surface independently.

Step 6 — Structural Factor cscd (Section 6)

The structural factor accounts for:

• The lack of full correlation of peak pressures on the surface (size effect, cs)
• The dynamic amplification due to turbulence and structural vibration (dynamic effect, cd)

cscd for Rigid Buildings

For buildings with height < 15 m, or where the fundamental frequency n1 >= 5 Hz, the structural factor may be taken as:

[ c_s c_d = 1.0 ]

Simplified Determination

For rectangular buildings with common structural materials and height < 100 m, EN 1991-1-4 Figure 6.1 provides cscd as a function of height and building dimension. For a typical 5-storey steel office (h = 20 m, n1 ~ 2 Hz):

• cscd ≈ 0.95–1.05, depending on the along-wind dimension
• The default cscd = 1.0 is conservative and widely used for buildings under 30 m

For slender structures (h/d > 5), chimneys, masts, and bridges, the detailed procedure in Clause 6.3 must be used, which requires the mechanical admittance function, spectral density of turbulence, and the logarithmic decrement of structural damping.

Step 7 — Force Coefficient cf (Section 8)

For building frames where individual surface pressures are resolved into structural loads, the overall wind force on a surface or segment is:

[ Fw = c_s c_d \times c_f \times q_p(z_e) \times A{ref} ]

Alternatively, for buildings where the pressure distribution is needed for frame analysis, the surface pressure approach is used:

[ w*{net} = q_p(z_e) \times c*{pe} - qp(z_i) \times c{pi} ]

Most steel frame analyses use the surface pressure approach because it provides the pressure distribution needed for frame member design, rather than a single overall force.

Step 8 — Worked Example: Steel-Framed Office Building in Berlin

Given:

• Location: Berlin, Germany (vb,0 = 25.0 m/s)
• Building: 40 m wide x 25 m deep x 15 m eaves height
• Flat roof, no significant parapet (hp/h < 0.025)
• Terrain Category III (suburban, mixed development)
• cdir = 1.0, cseason = 1.0
• c0(z) = 1.0 (flat terrain, no orography)
• rho = 1.25 kg/m^3
• Enclosed, uniformly distributed openings (cpi = +0.2, -0.3)
• Rigid building (steel frame, n1 > 5 Hz): cscd = 1.0

Step 8a — Basic Velocity Pressure qb

[ v_b = 1.0 \times 1.0 \times 25.0 = 25.0 \text{ m/s} ] [ q_b = \frac{1}{2} \times 1.25 \times (25.0)^2 = 0.5 \times 1.25 \times 625 = 390.6 \text{ Pa} = 0.391 \text{ kPa} ]

Step 8b — Peak Velocity Pressure at Roof Height (z = 15 m, Cat III)

At z = 15 m, Category III: z0 = 0.3 m, zmin = 5 m.

[ k_r = 0.19 \times (0.3/0.05)^{0.07} = 0.19 \times 6^{0.07} = 0.19 \times 1.134 = 0.215 ]

[ c_r(15) = 0.215 \times \ln(15/0.3) = 0.215 \times \ln(50) = 0.215 \times 3.912 = 0.841 ]

Turbulence intensity: [ I_v(15) = \frac{1.0}{1.0 \times \ln(15/0.3)} = \frac{1.0}{3.912} = 0.256 ]

Peak velocity pressure: [ q_p(15) = [1 + 7 \times 0.256] \times 0.5 \times 1.25 \times [0.841 \times 25.0]^2 ] [ q_p(15) = [1 + 1.792] \times 0.5 \times 1.25 \times (21.03)^2 ] [ q_p(15) = 2.792 \times 0.625 \times 442.1 = 2.792 \times 276.3 = 771.3 \text{ Pa} = 0.771 \text{ kPa} ]

Or using the exposure factor: ce(15) for Category III from Figure 4.2 ≈ 2.0: qp(15) = 2.0 x 0.391 = 0.782 kPa (matches within calculation rounding).

Adopt qp = 0.77 kPa at roof height.

Step 8c — External Pressure Coefficients cpe

h/d = 15/25 = 0.60.

Windward wall (Zone D): interpolate between h/d = 0.25 (cpe = +0.70) and h/d = 1.0 (cpe = +0.80): cpe = 0.70 + (0.60 — 0.25) x (0.80 — 0.70) / 0.75 = 0.70 + 0.35 x 0.133 = 0.75.

Leeward wall (Zone E): interpolate between -0.30 (h/d = 0.25) and -0.50 (h/d = 1.0): cpe = -0.30 + (0.60 — 0.25) x (-0.50 — (-0.30)) / 0.75 = -0.30 — 0.35 x 0.267 = -0.39.

Side walls: cpe = -0.80 (Zone B, dominant zone for frame analysis).

Flat roof: cpe = -0.70 (Zone H, interior). Corner Zone F = -1.80 is for cladding design only.

Step 8d — Design Wind Pressures

With cpi = +0.2 and cpi = -0.3 applied independently.

Windward wall, cpi = -0.3 (internal suction adds to push): [ w_D = 0.77 \times 0.75 - 0.77 \times (-0.3) = 0.77 \times (0.75 + 0.30) = 0.77 \times 1.05 = 0.81 \text{ kPa} ]

Windward wall, cpi = +0.2: [ w_D = 0.77 \times 0.75 - 0.77 \times 0.2 = 0.77 \times 0.55 = 0.42 \text{ kPa} ]

Governing: wD = +0.81 kPa (positive, toward building).

Leeward wall, cpi = +0.2 (internal pressure adds to suction): [ w_E = 0.77 \times (-0.39) - 0.77 \times 0.2 = 0.77 \times (-0.59) = -0.45 \text{ kPa} ]

Leeward wall, cpi = -0.3: [ w_E = 0.77 \times (-0.39) - 0.77 \times (-0.3) = 0.77 \times (-0.09) = -0.07 \text{ kPa} ]

Governing: wE = -0.45 kPa (suction).

Roof, cpi = +0.2: [ w_H = 0.77 \times (-0.70) - 0.77 \times 0.2 = 0.77 \times (-0.90) = -0.69 \text{ kPa} ]

Roof, cpi = -0.3: [ w_H = 0.77 \times (-0.70) - 0.77 \times (-0.3) = 0.77 \times (-0.40) = -0.31 \text{ kPa} ]

Governing: wH = -0.69 kPa (uplift suction).

Step 9 — Summary of Design Wind Pressures

Total horizontal load on building per metre width: For a 5 m frame spacing and 15 m height: Per frame: Fh = (0.81 + 0.45) x 15 x 5 = 1.26 x 75 = 94.5 kN per frame

Comparison: EN 1991-1-4 vs ASCE 7-22

Frequently Asked Questions

Why does EN 1991-1-4 use a 10-minute mean wind speed while ASCE 7 uses a 3-second gust?

The 10-minute mean represents a quasi-static wind reference that separates the mean flow from the turbulent gust response (captured separately through the peak velocity pressure qp and structural factor cscd). The 3-second gust bundles both into a single value, requiring a lower gust factor. When comparing equivalent design pressures, the peak velocity pressure qp in EN 1991-1-4 is roughly comparable to qz x G in ASCE 7. For example, vb,0 = 25 m/s (10-min) with Category II yields qp ≈ 0.7–0.9 kPa at 10 m, while V = 54 m/s (3-s gust) yields qz x G ≈ 18 psf ≈ 0.86 kPa — similar order of magnitude. The codes differ in the partitioning of mean vs gust effects, not in the overall structural safety level.

How do I handle the National Annex variations across European countries?

Each EU/EEA country publishes its own National Annex (NA) to EN 1991-1-4 that may override: (a) the fundamental wind velocity map vb,0, (b) the terrain categories or z0/zmin values, (c) the cdir and cseason recommended values, (d) the air density rho, (e) the pressure coefficient tables, and (f) the partial factor gamma_Q for wind. Always obtain the NA for the country where the building is located. The German NA (DIN EN 1991-1-4/NA), for example, provides a detailed wind zone map with vb,0 from 22.5 to 30.0 m/s. The UK NA provides a fundamentally different wind speed map with directional and seasonal factors set to 1.0 and specific orography rules. Never use the "recommended" EN values without checking the local NA — the differences can be 20% or more.

When should I use the force coefficient method (Section 8) instead of the surface pressure method (Section 7)?

The surface pressure method (cpe approach) is used for buildings where the pressure distribution over the surface is needed for structural analysis — this applies to most multi-storey frames, shear walls, and portal frames. The force coefficient method (cf approach) is used for: (a) lattice towers and trusses where individual member forces are resolved by a single cf value, (b) signboards, free-standing walls, and parapets where only the total force on the element is required, (c) circular cylinders and spheres where pressure coefficients vary significantly around the circumference, and (d) overall building stability checks where only total base shear is needed. For a typical steel-framed building, use the surface pressure method.

What is the practical effect of the orography factor c0 on structural design?

For sites on hills, ridges, or escarpments, c0 can increase the effective wind speed by 10–70% (c0 = 1.1–1.7). The procedure in Clause 4.3.3 and Annex A.3 requires the hill height H, upwind slope length Lu, and building position relative to the crest. For a building positioned at the crest of a 30 m hill in flat country (Category II): c0(x=0, z=15m) ≈ 1.25 + additional height-dependent factor, potentially reaching 1.5 at the crest. This directly scales qp by c0^2, so a c0 = 1.5 increases the wind pressure by 125%. Topographic amplification is often the single most overlooked wind load factor and must be assessed by site inspection or topographic survey.

How do I select between the simplified cscd = 1.0 and the detailed dynamic procedure?

Use cscd = 1.0 when: (a) building height < 15 m, or (b) fundamental frequency n1 > 5 Hz, or (c) height/depth ratio h/d < 3 for rectangular buildings with normal structural damping. Use the detailed procedure (Clause 6.3) when: (a) building height > 50 m, (b) slender building with h/d > 5, (c) fundamental frequency n1 < 1 Hz, (d) lightweight steel frames where wind-induced vibration could be perceptible, (e) bridge decks, chimneys, or masts. For a 15 m steel frame, n1 is typically 2–5 Hz, the building is rigid, and cscd = 1.0 is fully justified. For a 70 m steel tower (n1 ≈ 0.8 Hz), the detailed procedure would calculate cscd ≈ 1.05–1.15, adding 5–15% to the design force — significant for the cost of the lateral system.

Reference only. Verify all values against the current edition of EN 1991-1-4:2005 + A1:2010, including the National Annex for the project country. This guide does not constitute professional engineering advice and must be independently verified by a chartered or licensed structural engineer for the specific project location, terrain conditions, and governing building regulations.