Step-by-step wind load calculation for buildings in Turkey: the simplified TS 498 method for preliminary design and the detailed TS EN 1991-1-4 procedure including terrain categories, mean wind speed profile, peak velocity pressure, and external/internal pressure coefficients — with a worked example for an 8-storey residential building in İzmir.
Two standards are used for wind load calculation on buildings in Turkey:
| Region | Prevailing Wind | vb,0 (m/s) | Notes |
|---|---|---|---|
| Aegean coast (İzmir, Çeşme) | Meltemi (summer N-NW), Poyraz | 33–36 | Channelling in bays amplifies local speed |
| Marmara (İstanbul, Çanakkale) | Poyraz (NE), Lodos (SW) | 30–33 | Boğaz funnelling can reach 40+ m/s locally |
| Black Sea coast (Zonguldak, Rize) | N-NE predominantly | 33–38 | High rainfall increases effective pressure |
| Inner Anatolia (Ankara, Konya) | Variable, W dominant | 28–32 | Lower speeds, lower turbulence inland |
| Eastern Anatolia (Erzurum) | N-NE winter dominant | 30–35 | High altitude increases density; snow combination governs |
| Mediterranean coast (Antalya, Mersin) | W-SW, Gündoğusu | 28–32 | Milder but combined with heavy seismic |
TS 498 §12 calculates wind pressure as a function of height using a basic dynamic pressure qk that varies with height z above ground. No regional wind speed map is provided — a uniform conservative value is used for the whole country:
| Height above ground z (m) | qk(z) (kN/m²) |
|---|---|
| 0 – 8 | 0.40 |
| 8 – 16 | 0.55 |
| 16 – 25 | 0.65 |
| 25 – 40 | 0.80 |
| 40 – 60 | 1.00 |
| 60 – 80 | 1.10 |
| 80 – 100 | 1.20 |
| > 100 | Special study required |
Ce = exposure factor (0.80 for sheltered terrain; 1.00 for open country; 1.20 for exposed coastal sites). Cp = pressure coefficient (typically 0.8 for windward face; −0.4 for leeward; combined 1.2 for building drag). These simplified values are conservative and provide a quick check for low-rise structures.
TS EN 1991-1-4 defines terrain roughness through five terrain categories that determine how wind speed varies with height:
| Terrain Category | Description | z0 (m) | zmin (m) |
|---|---|---|---|
| 0 | Sea, coastal areas exposed to open sea | 0.003 | 1 |
| I | Lakes, flat terrain with negligible vegetation | 0.01 | 1 |
| II | Open country with low vegetation, isolated obstacles | 0.05 | 2 |
| III | Suburban, industrial areas, forests | 0.3 | 5 |
| IV | Urban areas with > 15% coverage by buildings > 15 m | 1.0 | 10 |
z0 = roughness length; zmin = minimum height for terrain model validity. In practice, most Turkish urban locations use Category III (suburban) or Category IV (dense urban). Coastal İzmir near the sea would use Category 0 or I for the windward face.
cdir = directional factor (= 1.0 per Turkish National Annex, all directions); cseason = seasonal factor (= 1.0 for annual design); vb,0 = fundamental basic wind speed. Per Turkish NA, vb,0 = 30 m/s is the standard value for most inland and suburban locations. Coastal and elevated sites use higher values per site-specific meteorological assessment.
c0(z) = orography factor (= 1.0 for flat terrain; values > 1.0 for hills and escarpments). The turbulence intensity Iv(z) = σv/vm(z) = kI/(c0·ln(z/z0)) where kI = 1.0 per Turkish NA.
The factor [1 + 7·Iv] accounts for gustiness — the 1 represents the mean wind component, while 7·Iv captures the gust peak. For Terrain Category II at z = 10 m with vb = 30 m/s:
External pressure coefficients Cpe depend on building geometry (h/d ratio) and zone (windward, leeward, side walls, roof):
| Zone | Cpe,10 (A ≥ 10 m²) | Cpe,1 (A = 1 m²) |
|---|---|---|
| D — Windward vertical wall | +0.8 | +1.0 |
| E — Leeward vertical wall | −0.6 to −0.5 | −0.6 to −0.5 |
| A — Side wall (near edge) | −1.2 | −1.4 |
| B — Side wall (mid) | −0.8 | −1.1 |
| C — Side wall (far) | −0.5 | −0.5 |
| F — Flat roof (corner) | −1.8 | −2.5 |
| G — Flat roof (edge) | −1.2 | −2.0 |
| H — Flat roof (interior) | −0.7 | −1.2 |
| I — Flat roof (interior far) | +0.2 / −0.2 | — |
Internal pressure coefficients Cpi depend on the building permeability. For buildings with uniformly distributed openings: Cpi = +0.2 or −0.3 (both must be checked). Net pressure is: wnet = qp(z) · (Cpe − Cpi).
The structural factor cscd accounts for background and resonant dynamic response. For buildings with natural frequency n1 > 1 Hz (height ≤ 50 m for typical RC frames), cscd = 1.0 per simplified procedure of EN 1991-1-4 §6.2.
The characteristic wind force is then used in the TSC load combinations: U3 = 1.2G + Q + 1.6W or U4 = 0.9G + 1.6W.
| Feature | TS 498:1997 | TS EN 1991-1-4 | ASCE 7-22 |
|---|---|---|---|
| Basic wind speed | Implicit in qk table (≈ 45 m/s equivalent) | vb,0 = 10-minute mean (Turkey NA: 30–36 m/s) | V = 3-second gust (LRFD, 40–75 m/s) |
| Averaging time | Not explicit (≈ 10 min) | 10-minute mean wind speed | 3-second gust (fundamental) |
| Terrain model | Exposure factor Ce (3 categories) | 5 terrain categories (z0-based) | 3 exposure categories (B, C, D) |
| Height profile | Step function (7 height bands) | Logarithmic law | Power law: (z/zg)2/α |
| Gust factor | Implicit (conservative static approach) | [1 + 7·Iv] gust factor | G = 0.85 (rigid); detailed for flexible |
| Pressure coefficients | Cp = ±0.8/0.4 (simplified) | Cpe from Figures 7.1–7.13 | GCp from ASCE 7 Figures 27–30 |
| Load factor | 1.6 (TSC combination) | 1.6 (EN 1990 / TSC) | 1.0 (already in LRFD wind speed) |
| Return period | Not specified (≈ 50 yr) | 50 yr (10-min mean) | 700 yr (risk cat II, LRFD) |