Practical Engineering: Simple Beam Sizing

The fundamental structural element in a building is the beam, a horizontal member that supports something. It’s used everywhere in wood-framed structures — joists, headers, girders. In the next two columns, I’d like to show you how we engineers size these beams (headers and girders at least; for joists, you just use the tables). This month we’ll go into the raw strength of a beam; next month we’ll consider shear, deflection, and bounciness. All beams, whether wood, steel, concrete, or composite, have five principal properties of interest to the structural engineer: support configuration, cross-section, material, length, and load. From these five properties, we can usually determine whether the beam will do the job. All these properties apply to the wood members found