What’s a Box Beam?

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Box beams are structural beams used in construction, often made of steel, with enclosed cells for structural integrity. They can support more weight and resist torsional damage. Box girder bridges are often used for curved or bent designs, and can be made with tapered or multi-cell designs. However, they can be more expensive to manufacture and require regular maintenance.

A box beam is a type of structural beam used in construction that is most often made from steel, although in the past, iron was commonly used for construction purposes. This type of beam uses one or more enclosed cells within the beam for structural integrity, as opposed to an I-beam or H-beam, both of which have open ends. Bridge construction will often require the use of box girder, as will other structures such as buildings. This type of beam can usually support more weight than an I-beam and will be more resistant to torsional damage or twisting.

Bridges are sometimes built in a box girder design on a much larger scale. Bridges that curve or bend particularly benefit from this design due to the box girder’s ability to resist twisting. Concrete can actually be poured into the appropriate form, usually under the bridge deck, to add torsional stiffness to the overall structure. The box beam design may feature only one cell or box, while other designs may feature a multi-cell system including many boxes. Even the shape of the box is not always rectangular; each box can be tapered to accommodate a specific design for the structure. This is sometimes called a cellular beam design.

The disadvantages of a box beam can prevent its regular use. These beams are generally more expensive to manufacture and can be more susceptible to rust and corrosion because water can begin to collect within the cell of the beam. Several bridges using the box girder design have collapsed in the past, leading to a re-evaluation of the utility and safety of the design for bridge design. Many bridges are still built with this technique, however, without major safety risks.

A significant advantage of box beams is the ability to support a significant amount of weight in the same length compared to an I-beam. Structures can therefore be built taller, wider, or longer using box beams as opposed to other designs. The multi-cell design can further increase strength, making it possible to build long bridges over large spans. The bridge and other structures, however, will often require more regular inspection and maintenance to ensure that the girders are still strong, well conditioned and capable of withstanding the normal stresses of the structure. Such inspections and maintenance can become expensive, and combined with the overall manufacturing cost of materials, the structure can become cost-prohibitive to build with such beams.




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