A is a structural member usually consisting of at least two or more different materials that are joined together that result in a stronger system than each individual part. 

How a Composite Beam Works:

A steel beam with a concrete slab on top of metal decking which is, usually connected with shear studs, act together to resist the overall load on the beam.

Why Does a Composite Beam Matter:

By physically attaching the parts together, the resulting system is stronger the the sum of each part. In a composite beam the concrete absorbs most of the compression, while the steel takes most of the tension.