The terms composite beam and reinforced beam are applied to beams that are
made of two or more di¤erent materials. Usually, the material that forms
the bulk of a composite beam is inexpensive but not sufficiently strong in
bending to carry the loading by itself. The function of the reinforcement is to
increase the flexural strength of the beam.
The flexure formula s ¼ My=I derived in Sec. 5.2 does not apply to
composite beams because it is based on the assumption that the beam is
homogeneous. However, we can modify the formula by transforming the
composite cross section into an equivalent homogeneous section that has
the same bending sti¤ness. The other assumptions made in the derivation of