Commercial Building Inspector B2Structural SystemsMedium
A commercial building inspector is reviewing the structural plans for a new school gymnasium. The roof framing consists of open web steel joists (OWSJ). The plans specify that bridging is required for these joists. According to AISC specifications and typical industry practice referenced by the IBC, what is the primary purpose of bridging in open web steel joists?
- ATo transfer lateral loads from the roof diaphragm to the shear walls.
- BTo increase the flexural strength of the joists under concentrated loads.
- CTo facilitate the attachment of ceiling finishes and mechanical systems.
- DTo provide lateral stability to the compression chords and prevent buckling.
Show answer & explanationAnswer & explanation
Correct answer: D. To provide lateral stability to the compression chords and prevent buckling.
Bridging in open web steel joists, whether horizontal or diagonal, is primarily installed to provide lateral support to the compression chords of the joists. This lateral restraint prevents the relatively slender compression chords from buckling out of plane under vertical load, thus ensuring the joist's overall stability and load-carrying capacity. While it can contribute to diaphragm action, its main purpose is local stability.
Why the other options are wrong
- A. While bridging can contribute to diaphragm action, its primary role is not to transfer lateral loads from the roof diaphragm; that is the role of the diaphragm itself and its connections.
- B. Bridging does not significantly increase the flexural strength of the joists; it addresses stability issues.
- C. Bridging may incidentally provide some attachment points, but this is not its primary structural purpose.
Steel Joist Bridging
Lateral bracing elements (horizontal or diagonal) installed between open web steel joists to stabilize the compression chords and prevent buckling.
- Essential for lateral stability of OWSJ.
- Prevents out-of-plane buckling of compression chords.
- Required at specified intervals along the joist span.
Memory trick: Joist chords need bridging to stand tall, not fall.