Structural Loads

A load is any force or effect applied to a structure. Proper load determination is the first step in structural design.

Types of Loads

Dead Load (D)

• Permanent, self-weight of structure
• Examples: concrete slab, steel beams, roofing
• Calculated from material densities × volume

Live Load (L)

• Moveable, occupancy-dependent
• Defined by ASCE 7 Table 4.3-1
• Examples: people, furniture, equipment
• Typical values: 40 psf (residential), 50 psf (office), 100 psf (assembly)

Wind Load (W)

• Lateral pressure from wind
• Depends on: wind speed, exposure category, building height
• ASCE 7 Chapter 26–31

Snow Load (S)

• Ground snow load × roof factor
• ASCE 7 Chapter 7

Seismic Load (E)

• Inertial forces from ground motion
• Based on seismic design category

Load Combinations (ASCE 7 Section 2.3)

For strength design (LRFD):

1.4D
1.2D + 1.6L + 0.5(Lr or S or R)
1.2D + 1.6(Lr or S or R) + (L or 0.5W)
1.2D + 1.0W + L + 0.5(Lr or S or R)
0.9D + 1.0W

Tributary Area

The tributary area of a structural member is the floor/roof area it supports.

Example: A beam spaced 10 ft apart spanning 20 ft has a tributary area of 10 × 20 = 200 ft².

Load on beam = Load intensity (psf) × Tributary area (ft²)

Summary

Always apply load combinations per ASCE 7. The governing load combination produces the maximum design force used in member sizing.