TS EN 1991-1-4 – Wind Load Calculation

TS EN 1991-1-4 (Eurocode 1-4) defines façade wind actions in terms of building height, terrain roughness, orography and direction/season factors. The steps below show how to obtain the characteristic load for stick curtain-wall systems.

The procedure follows 7 core steps from the standard:

1. Basic Wind Velocity (V_b)

The map value V_b,0 is multiplied by direction (C_dir) and season (C_season) factors:

V_b = C_dir × C_season × V_b,0

2. Terrain Factor (K_r)

With roughness length z₀:

K_r = 0.19 · (z₀/0.05)^0.07

3. Roughness Coefficient (C_r(z))

Obtained by multiplying K_r by ln(z / z₀):

C_r(z) = K_r · ln(z / z₀)

4. Mean Wind Velocity (V_m(z))

V_m(z) = C_r(z) × C_o(z) × V_b

5. Turbulence Intensity (I_v(z))

I_v(z) = K₁ / [C_o(z) · ln(z / z₀)]

6. Peak Velocity Pressure (q_p(z))

q_p(z) = 0.5 · ρ · V_m(z)² · [1 + 7 · I_v(z)]

7. Net Surface Pressure (w)

w = q_p(z) · (C_pe − C_pi)

In practice different C_pe values are taken for ZONE A (suction) and ZONE D (pressure). For sealed façades C_pi is commonly set to 0.

8. Recommended External Pressure Coefficients – Table 7.1

Table 7.1 of TS EN 1991-1-4 gives characteristic external pressure coefficients (C_pe,10 and C_pe,1) for vertical walls of rectangular-plan buildings. h/d is the ratio of building height to plan depth.

h/d	Zone A		Zone B		Zone C		Zone D		Zone E
h/d	C_pe,10	C_pe,1	C_pe,10	C_pe,1	C_pe,10	C_pe,1	C_pe,10	C_pe,1	C_pe,10	C_pe,1
5	-1.2	-1.4	-0.8	-1.1	-0.5	-0.5	+0.8	+1.0	-0.7	–
1	-1.2	-1.4	-0.8	-1.1	-0.5	-0.5	+0.8	+1.0	-0.5	–
≤0.25	-1.2	-1.4	-0.8	-1.1	-0.5	-0.5	+0.7	+1.0	-0.3	–

Note — If wind force on both windward (Zone D) and leeward (Zone E) walls is applied simultaneously, correlation factors depending on h/d may be adopted: 1.00 for h/d ≥ 5, 0.85 for h/d ≤ 1; linear interpolation for intermediate ratios.

9. C_pe as a Function of Loaded Area

According to §7.2.1, use C_pe,1 for areas ≤ 1 m² and C_pe,10 for areas ≥ 10 m². For intermediate areas (1 m² < A < 10 m²) apply the logarithmic interpolation:

C_pe(A) = C_pe,1 − (C_pe,1 − C_pe,10) · log₁₀(A)

A is the loaded area in m². The curve matches C_pe,1 at 1 m² and C_pe,10 at 10 m², decreasing linearly in log-space (see Figure 7.2).

Example — A = 3 m² panel

From Table 7.1, Zone A: C_pe,1 = −1.4, C_pe,10 = −1.2
log₁₀(3) ≈ 0.477
C_pe(3 m²) = −1.4 − (−1.4 − (−1.2)) × 0.477 ≈ −1.31

National Annexes may specify additional procedures or safety factors for areas > 10 m².

10. Numerical Verification

Beus Facade validates the resulting w values in FEM simulations, checking deflection limits, profile stresses and fixing safety.

TS EN 1991-1-4 – Wind Load Calculation

1. Basic Wind Velocity (Vb)

2. Terrain Factor (Kr)

3. Roughness Coefficient (Cr(z))

4. Mean Wind Velocity (Vm(z))

5. Turbulence Intensity (Iv(z))

6. Peak Velocity Pressure (qp(z))