Which of the following is NOT a type of beam?

A round beam is not a standard type of beam used in construction. Beams are structural elements that support loads and are commonly categorized by their cross-sectional shapes, which include rectangular, I-beams, and box beams.

Rectangular beams are popular due to their straightforward shape and effective load distribution. I-beams have a distinctive 'I' shape that provides a high strength-to-weight ratio, making them highly efficient for supporting heavy loads over long spans. Box beams are hollow and often used for applications requiring high torsional rigidity and low weight.

The round shape is not prevalent in structural beam applications because it does not provide the necessary support characteristics typically required in construction. Structures generally favor flat, wide surfaces for load distribution, which the standard beam shapes easily achieve. Consequently, the round beam does not fit into the conventional beam categories used in the construction industry.