A building beam is a structural element that supports the load of a structure. It is composed of joists, girders, DEFT, ibar, and tbar. Joists are horizontal members that support floors and ceilings. Girders are large beams that span long distances and support heavy loads. DEFT is a type of steel beam that is used to support heavy loads. Ibar and tbar are types of steel beams that are used to support lighter loads. All of these components work together to form a building beam, which is essential for the stability and strength of a structure.