Load-bearing beams can be constructed from a variety of materials, including timber, steel and reinforced concrete, depending upon the precise application.
The bearing capacity of a timber beam is determined by the crushing strength of the timber fiber. Like dry density, bearing capacity depends on the thickness of the cell walls in any given timber species, so dry density is often a good indicator of bearing capacity.
The application of a heavy, concentrated load to a steel beam or girder can induce high stress in the area of the beam immediately beneath the load. This can cause outward buckling of the area, and it may be necessary to insert a plate to spread out the load.
Concrete beams are commonly used in structural design. When a load is applied to a concrete beam, the bottom of the beam must stretch, or become longer, while the top of the beam must contract, or become shorter. Building designers must take these compressive forces into account when calculating the bearing capacity of a beam.