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Ultimate limit state combinations are implemented according to
Thus table gives the the load combinations that are to be generated using the load types types D, L, S and W. . The comments below the table explain how to extend this to the load types Ds, Lf/s, H and E.
Load Type |
Combination |
Case |
D |
1.4D |
1 |
D,L |
1.25D + 1.5L plus D only |
2 |
D,S |
1.25D + 1.5S plus D only |
3 |
D,W |
1.25D + 1.4W plus D only |
4 |
D,L,W |
1.25D + 1.5L + 0.4W 1.25D + 1.4W + 0.5L plus D,L; D,W, and D |
2 4 |
D,L,S2 |
1.25D + 1.5L + 1.0S2 1.25D + 1.5S + 1.0L2 plus D; D,L and D,S |
2 3 |
D,S,W |
1.25D + 1.5S + 0.4W 1.25D + 1.4W + 0.5S plus D; D,S and D,W |
3 4 |
D,L,W,S |
D; D,L,S; D,L,W; D,W,S; (no combinations with all of L, S, W) |
2 3 4 |
1 Note that this creates two extra load cases by splitting up D + S and D + L compared to what is required by the design code.
2 These combinations will only be created if not on an exterior surface- refer to the setting for this feature.
Combinations with more than 2 variable loads
To comply with NBC Structural Commentary A23, there are now no load combinations with live, wind and snow loads together. Exception: Load combinations are created containing sustained live loads along with wind and snow, for example 1.25D + 1.5W + 0.5Lf + 0.5S
Live and Snow on Exterior Surface
To comply with NBC 4.1.5.5, a setting allows you to create a set of load combinations without live and snow loads in the same combination. When the setting is checked, the program will omit those combinations that have both live (L, Ls or Lf) loads and snow (S) loads. If the program would ordinarily create combinations with L + S together but not separately, then the L-only or S-only combination is created
Dead Loads Due to Soil
The load combinations for Dead (soil) load types are arrived at by replacing D with D + Ds in this table, without repeating the load combinations for D only. The main Load Combinations page gives a list of combinations that contain Ds.
Hydrostatic Loads
The load combinations for hydrostatic loads H can be arrived at by adding H to each of these combinations, while also retaining the combinations without H. Refer to Hydrostatic Load Combinations for a list of these combinations and explanation.
Sustained Live Loads Ls and Lf
Sustained live loads are not included in this table. In general, Replace L by L + Ls if such loads occur, with the appropriate factors, without also repeating all of the load combinations that have L only, or creating combinations with Ls only. An exception to the above is that the load combinations D (+ Ds + H) + L and D ( + Ds + H) + Ls will be created.
In other words, for D, L, Ls, S, the following are created:
And the following are not created:
Refer to Sustained Load Combinations for a complete list of sustained load combinations and explanation.
Earthquake Loads
Earthquake loads are not included in this table. Refer to Earthquake Load Combinations for a list of these combinations and explanation.
Pattern Loads
Combinations containing only permanent loads D, Ds or H and either L and/or Ls/f loads or S loads, on multi-span members, will be patterned if you indicate that the particular loads are to be pattern loads. Refer to Pattern Loading.
The load types referred to here are D=dead W=wind S=snow H=earth,groundwater E=earthquake L=live(use,occupancy) Ls=live(storage,equipment) Lf =live(controlled fluids) ) Ds=dead load due to soil.