Frame load combinations
A frame is designed for the combination that hurts it, not for the largest single load. This builds the wind and seismic lateral loads from their own codes, applies the six ASCE 7 strength combinations, and re-solves the second-order frame for each one to find the governing case.
| Combination | Gravity (kN/m) | Lateral (kN) | Sway (mm) | Peak moment (kN·m) | Axial (kN) |
|---|---|---|---|---|---|
| 1.4D | 25.2 | 0.0 | 0.04 | 91.4 | 100.8 |
| 1.2D + 1.6L | 40.8 | 0.0 | 0.06 | 148.1 | 163.2 |
| 1.2D + 1.0W + L | 33.6 | 15.1 | 3.90 | 154.3 | 142.5 |
| 1.2D + 1.0E + L ◂ | 33.6 | 85.7 | 21.87 | 309.3 | 180.2 |
| 0.9D + 1.0W | 16.2 | 15.1 | 3.86 | 91.0 | 72.8 |
| 0.9D + 1.0E | 16.2 | 85.7 | 21.76 | 276.8 | 110.4 |
ASCE 7-22 §2.3.1 with snow, rain and roof live load omitted. Uplift combinations use 0.9D.
qz = 0.613 Kz Kzt Kd V² · N/m² with V in m/s.
Fw = qz G (Cp,w − Cp,l) A · Internal pressure cancels on a closed building.
V = Cs W, Cs = SDS/(R/Ie) · Capped by SD1/(T·R/Ie), floored at 0.044 SDS Ie.
1.2D + 1.0W + L · Six strength combinations, including two uplift cases.
A clear path from inputs to results.
A frame is designed for the combination that hurts it, not for the largest single load. This builds the wind and seismic lateral loads from their own codes, applies the six ASCE 7 strength combinations, and re-solves the second-order frame for each one to find the governing case.
How to use
- Set the frame geometry and section properties.
- Enter the dead and live load on the beams.
- Set the basic wind speed, the exposure category and the tributary width.
- Enter the seismic parameters and the seismic weight.
- Read the governing combination, the peak moment and the drift.
The formula
Reference: ASCE 7-22 §26.10 (velocity pressure), §12.8.1.1 (base shear) and §2.3.1 (strength combinations).
Worked example
Single-bay portal, 8 m span, 5 m eaves, 45 m/s wind, SDS 1.0
- Portal frame, 8 m span, 5 m eaves, 30,000 cm⁴ columns, 45,000 cm⁴ beams.
- Dead 18 kN/m, live 12 kN/m, tributary width 6 m.
- Wind 45 m/s, exposure C. Seismic SDS 1.0, SD1 0.6, R 6, T 0.7 s, W 1200 kN.
- 1
Kz at 5 m exposure C is 0.865, so qz = 0.613 × 0.865 × 0.85 × 45² = 913 N/m².
- 2
Net pressure 1.3 × 913 × 0.85 = 1,009 Pa over 30 m² gives 30 kN, 15.1 kN at each eave.
- 3
Cs = min(1.0/6, 0.6/(0.7 × 6)) = 0.1429, so V = 171 kN and 85.7 kN at each eave.
- 4
1.2D + 1.6L gives 148.1 kN·m; 1.2D + 1.0W + L gives 154.3 kN·m at 3.9 mm of sway.
- 5
1.2D + 1.0E + L governs: 309.3 kN·m at 21.9 mm, a drift of 1/229.
1.2D + 1.0E + L governs · 309.3 kN·m · 21.9 mm sway.
Interpreting the result
The seismic combination governs even though the wind force is five times smaller, because the code amplifies the seismic weight into a base shear far above the wind pressure on this small facade. That is the point of an envelope: the biggest number in the table is not the biggest load, it is the worst effect.
Assumptions & limitations
- Fixed bases and rigid beam connections; no bracing, no diaphragms and no torsional effects.
- Load effects are combined, not loads: the frame is re-solved for every combination.
- Snow, rain and roof live load are omitted; add them to the dead load if they matter.
- Second-order P-Δ effects are included in every run.
Frequently asked questions
Why re-solve instead of scaling one result?
Because gravity and lateral load change the frame differently. Scaling a wind result cannot tell you what the gravity case does, and the P-Δ softening depends on the axial force each combination produces.
What is an uplift combination?
0.9D + 1.0W or 0.9D + 1.0E: the dead load is reduced because wind or seismic can overturn the frame, and the minimum gravity load is what resists it.
Why does seismic beat wind here?
The base shear is a share of the whole building weight, while wind acts on the projected facade. For a stiff, heavy, small-footprint frame, seismic almost always wins.
Where is the drift limit?
ASCE 7 Table 12.12-1, typically 1/400 to 1/100 of the storey height depending on the risk category. This page reports the ratio so you can compare it.
Methodology last reviewed 2026-10-21. Results are informational and not financial or engineering advice — see our disclaimer.