Analysis & loading · Wind, snow & cyclone
Wind: site wind speed and building pressures (AS/NZS 1170.2) calculator
Regional and site wind speed with terrain, shielding and topographic multipliers, design pressure, wall and roof pressures for a rectangular building with the chosen internal pressure case, and the along-wind base shear and overturning moment.
Standard: AS/NZS 1170.2:2011 · VR (Table 3.1 formulae) · Mz,cat (Table 4.1(B)) · Ms, Mt, Md · Cpe Tables 5.2/5.3 · Cpi Table 5.1
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Inputs in the worked example
The live calculator starts with these values; change any of them and every result, check and diagram updates instantly.
| Input | Value | Unit |
|---|---|---|
| Wind region | B | |
| Annual exceedance 1/R (R years) | 500 | |
| Direction multiplier Md | 1 | |
| Terrain category | TC2.5 | |
| Shielding multiplier Ms | 1 | |
| Topographic multiplier Mt | 1 | |
| Average roof height h | 8 | m |
| Building width normal to wind b | 20 | m |
| Building depth parallel to wind d | 12 | m |
| Internal pressure Cpi (positive case) | 0.2 | |
| Internal pressure Cpi (negative case) | -0.3 | |
| Area reduction Ka | 1 | |
| Local pressure factor Kl | 1 |
Worked example — results
| Result | Value | Unit |
|---|---|---|
| R^−0.1 | 0.537 | |
| Regional speed VR | 56.58 | m/s |
| Height for Mz (3–50 m) | 8.00 | m |
| Table row | 2.00 | |
| z(i) | 5.00 | m |
| z(i+1) | 10.00 | m |
| Mz(i) | 0.870 | |
| Mz(i+1) | 0.920 | |
| Mz,cat (interpolated) | 0.900 | |
| Site wind speed Vsit = VR·Md·Mz·Ms·Mt | 50.92 | m/s |
| Design pressure q = 0.5ρV² (ρ = 1.2) | 1.56 | kPa |
| Leeward Cpe (by d/b) | -0.500 | |
| Roof Cpe upwind zone (by h/d) | -1.03 | |
| Windward wall q(0.7KaKl − Cpi,neg) | 1.56 | kPa |
| Leeward wall q(Cpe − Cpi,pos) | -1.09 | kPa |
| Side walls q(−0.65 − Cpi,pos) | -1.32 | kPa |
| Roof upwind q(Cpe − Cpi,pos) (uplift) | -1.92 | kPa |
| Along-wind force q(0.7 − Cpe,lee)·b·h | 298.7 | kN |
| Overturning moment F·h/2 | 1,195 | kNm |
| Result: design wind pressure q | 1.56 | kPa |
- ✓ Height within the Mz,cat table (≤ 50 m)
- ✓ Building not dynamically sensitive (h ≤ 25 m assumed static)
Method, formulas and assumptions
- R^−0.1 = 500^-0.1 = 0.53716
- Regional speed VR = CHOOSE(3,67-41*0.53716,104-70*500^-0.045,106-92*0.53716,1.05*(122-104*0.53716),1.1*(156-142*0.53716)) = 56.581 m/s
- Height for Mz (3–50 m) = MIN(MAX(8,3),49.999) = 8 m
- Table row = MATCH(8,[mz.z],1) = 2
- z(i) = INDEX([mz.z],2) = 5 m
- z(i+1) = INDEX([mz.z],2+1) = 10 m
- Mz(i) = INDEX(CHOOSE(3,[mz.c1],[mz.c2],[mz.c25],[mz.c3],[mz.c4]),2) = 0.87
- Mz(i+1) = INDEX(CHOOSE(3,[mz.c1],[mz.c2],[mz.c25],[mz.c3],[mz.c4]),2+1) = 0.92
- Mz,cat (interpolated) = 0.87+(0.92-0.87)*(8-5)/(10-5) = 0.9
- Site wind speed Vsit = VR·Md·Mz·Ms·Mt = 56.581*1*0.9*1*1 = 50.923 m/s
- Design pressure q = 0.5ρV² (ρ = 1.2) = 0.6*50.923^2/1000 = 1.5559 kPa
- Leeward Cpe (by d/b) = IF(12/20<=1,-0.5,IF(12/20<=2,-0.5+0.2*(12/20-1),IF(12/20<=4,-0.3+0.05*(12/20-2),-0.2))) = -0.5
- Roof Cpe upwind zone (by h/d) = IF(8/12<=0.5,-0.9,IF(8/12>=1,-1.3,-0.9-0.8*(8/12-0.5))) = -1.0333
- Windward wall q(0.7KaKl − Cpi,neg) = 1.5559*(0.7*1*1--0.3) = 1.5559 kPa
- Leeward wall q(Cpe − Cpi,pos) = 1.5559*(-0.5*1*1-0.2) = -1.0891 kPa
- Side walls q(−0.65 − Cpi,pos) = 1.5559*(-0.65*1*1-0.2) = -1.3225 kPa
- Roof upwind q(Cpe − Cpi,pos) (uplift) = 1.5559*(-1.0333*1*1-0.2) = -1.9189 kPa
- Along-wind force q(0.7 − Cpe,lee)·b·h = 1.5559*(0.7--0.5)*20*8 = 298.73 kN
- Overturning moment F·h/2 = 298.73*8/2 = 1194.9 kNm
- Result: design wind pressure q = 1.5559 = 1.5559 kPa
- Values from the 2011 edition formulae as used elsewhere on this site; AS/NZS 1170.2:2021 revised the regions (A0–A5, B1, B2) and some multipliers, so check against the edition you design to.
- Cyclonic regions C and D include Fc/Fd = 1.05/1.1 in VR. Cpe zones simplified to the upwind roof zone and the leeward/side wall averages.
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For preliminary design and education. Check every result against the current standard and your own engineering judgement before use.