What is a bar joist?

A bar joist is specifically defined as an open-web steel truss. This type of truss is designed to support roofs or floors and is characterized by its lightweight and open web design, which allows for the efficient use of materials and the ability to run mechanical systems, such as ductwork, through the open spaces.

Bar joists typically consist of parallel top and bottom chords connected by vertical and diagonal members. This structure not only provides strength but also minimizes weight, which is beneficial in construction applications. They are commonly used in commercial and industrial buildings due to their versatility and strength-to-weight ratio.

In assessing other answers, it's important to note that while engineered components with steel load-bearing members certainly exist, they do not specifically define what a bar joist is. Similarly, a truss with steel parallel members and wood diagonals is not accurate, as bar joists are typically made entirely of steel. Lastly, a steel I-beam, while a crucial component in steel construction, serves a different structural purpose compared to the open web design of a bar joist.