Typical Load Combinations For Residential Buildings DesignArticles > Typical Load Combinations For Residential Buildings Design
|Component or System
||ASD Load Combinations
||LRFD Load Combinations
|Foundation wall (gravity and soil lateral loads)
||D + H
D + H + L + 0.3(Lr + S)
D + H + (Lr or S) + 0.3L
|1.2D + 1.6H
1.2D + 1.6H + 1.6L + 0.5(Lr + S)
1.2D + 1.6H + 1.6(Lr or S) + 0.5L
|Headers, girders, joists, interior load-bearing walls and columns, footings (gravity loads)
||D + L + 0.3 (Lr or S)
D + (Lr or S) + 0.3 L
|1.2D + 1.6L + 0.5 (Lr or S)
1.2D + 1.6(Lr or S) + 0.5 L
|Exterior load-bearing walls and columns (gravity and transverse lateral load)
||Same as immediately above plus
D + W
D + 0.7E + 0.5L + 0.2S
|Same as immediately above plus
1.2D + 1.5W
1.2D + 1.0E + 0.5L + 0.2S
|Roof rafters, trusses, and beams; roof and wall sheathing (gravity and wind loads)
||D + (Lr or S)
0.6D + Wu
D + W
|1.2D + 1.6(Lr or S)
0.9D + 1.5Wu
1.2D + 1.5W
|Floor diaphragms and shear walls (in-plane lateral and overturning loads)
||0.6D + (W or 0.7E)
||0.9D + (1.5W or 1.0E)
- The load combinations and factors are intended to apply to nominal design loads defined as follows: D = estimated mean dead weight of the construction; H = design lateral pressure for soil condition/type; L = design floor live load; Lr = maximum roof live load anticipated from construction/maintenance; W = design wind load; S = design roof snow load; and E = design earthquake load.
- Attic loads may be included in the floor live load, but a 10 psf attic load is typically used only to size ceiling joists adequately for access purposes. However, if the attic is intended for storage, the attic live load (or some portion) should also be considered for the design of other elements in the load path.
- The transverse wind load for stud design is based on a localized component and cladding wind pressure; D + W provides an adequate and simple design check representative of worst-case combined axial and transverse loading. Axial forces from snow loads and roof live loads should usually not be considered simultaneously with an extreme wind load because they are mutually exclusive on residential sloped roofs. Further, in most areas of the United States, design winds are produced by either hurricanes or thunderstorms; therefore, these wind events and snow are mutually exclusive because they occur at different times of the year.
- For walls supporting heavy cladding loads (such as brick veneer), an analysis of earthquake lateral loads and combined axial loads should be considered. However, this load combination rarely governs the design of light-frame construction.
- Wu is wind uplift load from negative (i.e., suction) pressures on the roof. Wind uplift loads must be resisted by continuous load path connections to the foundation or until offset by 0.6D.
- The 0.6 reduction factor on D is intended to apply to the calculation of net overturning stresses and forces. For wind, the analysis of overturning should also consider roof uplift forces unless a separate load path is designed to transfer those forces.
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