A steel I-beam is a type of joist or girder made from structural steel. I-beams are used as major support trusses in building, to ensure that a structure will be physically sound. Steel is one of the most common materials used to make I-beams, since it can withstand very heavy loads. Other materials such as aluminum are sometimes used to make I-beams, depending on their intended use. Composite I-beams are also available, with layers of other materials encasing the outside of the steel I-beam to disguise it as something else, such as wood.

The shape of a steel I-beam strongly resembles a capital “I” in cross section, which explains the name. The steel I-beam has a strong central core capped with flanges on either side. Various lengths of beam are available to suit construction project needs, and each steel I-beam also carries a rating, indicating how large it is, and how much weight it is able to bear. When engineers are designing a structure, they determine what the load limits of the I-beams used in the structure should be.

There are advantages and disadvantages to using steel I-beams in construction. They are much less likely to bend or warp than wood, allowing builders to use steel I-beams to create large open spaces which would not be possible with ordinary wooden beams. A steel I-beam also does not need to be as large as a wooden beam bearing the same load, so the support beams in a structure do not need to be so obtrusive. However, a steel I-beam can fail catastrophically if exposed to heat, making it necessary to insulate the beam for safety.

Several fabrication techniques are used to create steel I-beams. Many are rolled or extruded, processed on metalworking machinery which creates standardized beams very rapidly. Other steel I-beams, sometimes called plate girders, are made by riveting or welding together sections of steel plate. However the steel I-beam is manufactured, it will be extremely heavy, requiring strong workers and specialized equipment to be handled.

When a house is renovated, steel I-beams may be used to replace old structural supports. When removing structural supports, it is crucial to know how much weight they are supporting, and how they have been installed. For this reason, it is highly recommended that homeowners use professionally certified individuals for construction work which may involve removing such supports, to ensure that they do not compromise the structural integrity of the home.