In modern-day construction, a number of different steel beams are used. Steel is the material of choice for its durability, strength and availability. However, just what form the steel beam takes---whether typical I beams or some other type of beam---is up to the designers, the engineers and the needs and limitations of each project.
The most familiar type of steel beam is the I beam. Named because its cross section resembles the capital letter "I," the I beam is commonly used in large commercial and residential buildings and sometimes is used in smaller structures, including single-family homes. Steel I beams are also easy to modify in fabrication shops by cutting, drilling, and welding.
Box Girders and Channel Beams
Box girders are either square or rectangular steel tubes with hollow cores. Box girders are lighter than solid steel of the same dimensions but provide exceptional strength, which is why box girders are often used to build bridges (hence the name "box girder bridge").
A channel beam has a U-shaped cross section and looks like a long trough or channel, hence the name. The shape of a channel beam helps it support a larger load than a flat piece of steel the same thickness, but the smaller mass means that it weighs less than an I beam of the same basic dimensions.
A flitch beam is made from a steel core sandwiched between two sheets of wood. That layering effect makes flitch beams lighter than regular steel beams of the same dimensions, yet stronger and more durable than wooden beams of the same size. Flitch beams are lower-cost option than steel beams. Another advantage of the flitch beam is that it can be nailed to a wooden wall, making a flitch beam much easier to work with in many instances. Additionally, flitch beams can be made with architectural grade lumber that is meant to be exposed when the structure is finished.