In short: For metal buildings designed to US practice, wind is usually worked out either with the ASCE 7-16 directional procedure (Chapter 27: velocity pressure qz with the new ground elevation factor Ke, then G·Cp and GCpi) or with MBMA 2012 practice, which is based on ASCE 7-10 and uses the low-rise envelope coefficients (GCpf − GCpi) with end zones. They give different loads, so the project specification decides which you use. Wind Load calculates both, alongside IS 875, and applies the member loads to your STAAD.Pro model.
Pre-engineered and metal buildings for US and Middle East clients often specify "ASCE 7" or "MBMA" for wind, sometimes both in the same document. They are related but not the same, and mixing their coefficients is one of the most common errors in metal building wind design. This guide explains how each works and what to watch for.
Which code applies?
- ASCE 7 (Minimum Design Loads for Buildings and Other Structures) is the load standard referenced by the International Building Code. ASCE 7-16 is the edition referenced by IBC 2018 and 2021.
- MBMA publishes the Metal Building Systems Manual. The 2012 manual is based on IBC 2012 and ASCE 7-10. It doesn't create a separate wind code; it explains how to apply ASCE 7 loads to metal buildings and gives coefficient tables arranged for them.
So "MBMA 2012" really means ASCE 7-10 wind, as applied to metal buildings. It is not the same as ASCE 7-16. Always check which edition the project specification calls for.
ASCE 7-16: velocity pressure
The starting point is the velocity pressure at height z (equation 26.10-1):
qz = 0.00256 × Kz × Kzt × Kd × Ke × V² (psf, with V in mph)
In SI units the constant is 0.613 (N/m², with V in m/s).
- V: basic wind speed from the maps for the Risk Category (an ultimate, strength-level speed).
- Kz: velocity pressure exposure coefficient (Table 26.10-1), by exposure B, C or D and height.
- Kzt: topographic factor, 1.0 on flat ground.
- Kd: wind directionality factor, 0.85 for buildings (Table 26.6-1).
- Ke: ground elevation factor (Table 26.9-1). This is new in ASCE 7-16. It is 1.0 at sea level, reduces at higher elevations, and may always be taken as 1.0.
Directional procedure (Chapter 27)
For the main wind force resisting system (MWFRS) of an enclosed or partially enclosed building:
p = q × G × Cp − qi × (GCpi)
- G: gust effect factor, 0.85 for rigid buildings.
- Cp: external pressure coefficients for walls and roof (Figure 27.3-1), by L/B, h/L and roof angle.
- GCpi: internal pressure coefficient (Table 26.13-1): ±0.18 for enclosed buildings, ±0.55 for partially enclosed buildings, 0 for open buildings. ASCE 7-16 also adds a "partially open" classification.
Open buildings with free roofs use net pressure coefficients CN (Figures 27.3-4 to 27.3-7) instead.
Envelope procedure and MBMA practice
ASCE 7 also has an envelope procedure for low-rise buildings (Chapter 28), and this is the format MBMA's tables follow. Instead of separate Cp values per face, it uses combined coefficients (GCpf) for zones around the building:
p = qh × [(GCpf) − (GCpi)]
- Zones 1 to 6 cover the windward wall, roof and leeward surfaces.
- End zones 1E to 6E cover a strip of width 2a at each end of the building, where pressures are higher.
- In ASCE 7-10, a is 10% of the least horizontal dimension or 0.4h, whichever is smaller, but not less than 4% of the least horizontal dimension or 3 ft.
MBMA 2012 arranges these coefficients for metal building frames: transverse tables for the main frames (interior and end zone) and longitudinal tables for the bracing direction. ASCE 7-10 also sets a minimum MWFRS load of 16 psf on walls (and 8 psf on roofs) projected on a vertical plane.
Key differences at a glance
| ASCE 7-16 directional | MBMA 2012 (ASCE 7-10) | |
|---|---|---|
| Velocity pressure | qz = 0.00256 Kz Kzt Kd Ke V² | qh = 0.00256 Kz Kzt Kd V² |
| Ground elevation factor Ke | Yes (new in 7-16) | No |
| Coefficients | G·Cp per face, GCpi | (GCpf − GCpi) by zone |
| End zones | Not used for MWFRS | Yes, width 2a (1E to 6E) |
| Typical use | General buildings, specs calling ASCE 7-16 | Metal buildings to MBMA practice |
Because the coefficient formats differ, never take Cp values from one method and use them in the other.
Applying it in STAAD.Pro
STAAD.Pro's ASCE 7 wind dialog works out Kz, Kzt, Kd, Ke, G, Cp and GCpi, but each wall needs its own load type, and as with any panel-based generator, sloped roof members need care. STAAD's wind dialog list has no MBMA-specific option. For metal building frames, most engineers calculate the pressures, then apply member UDLs to the columns and rafters:
UDL = pressure × tributary width × net coefficient, signed for each surface, for every wind direction and both internal pressure cases.
Doing both with Wind Load in SS Workbench
Wind Load in SS Workbench calculates the wind pressure to ASCE 7-16, MBMA 2012 (ASCE 7-10) or IS 875 (Part 3):2015, and applies the member loads to your STAAD.Pro model through the free STAAD Connector.
- ASCE 7-16: directional procedure, exposure B, C or D, Ke from ground elevation, Cp from Figure 27.3-1 for walls and roof, GCpi for enclosed, partially enclosed or open buildings, in SI or US units. Open buildings use the free-roof CN figures.
- MBMA 2012: qh from Kz, Kzt, Kd and V (or entered directly), (GCpf − GCpi) for the main frames with interior and end zones, transverse and longitudinal tables, and a check on the minimum 16 psf MWFRS load.
- Auto tag the walls and roof of the frames you select, with tributary width suggested from the frame spacing.
- 4, 6 or 8 load cases, every load shown in the 3D view before it is written.
- Apply to STAAD: add to your existing wind load cases or replace what they hold.
- A detailed calculation with clause references, printable as PDF.
It writes member UDLs into load cases that already exist in your model; it doesn't create load cases or combinations, or calculate cladding (components and cladding) pressures. It covers rectangular gable and mono-slope buildings, and the MBMA method stops above a 45° roof angle. Check the results before use, as with any design tool.
Working to Indian codes instead? Read IS 875 Part 3 wind load in STAAD.Pro.
Try it
Open Wind Load in SS Workbench, pick ASCE 7-16 or MBMA 2012, and compare the frame loads for the same building. The difference is often worth knowing before you agree the specification.