A truss manufacturer's design drawings specify continuous lateral bracing on the bottom chord of a series of roof trusses at 10-foot intervals to prevent buckling. During construction, a framer decides to omit this bracing because the trusses appear stable once sheathed on top. What is the risk of this decision?
- AThe ridge board will separate from the top chords
- BThe unbraced bottom chord can buckle laterally under compression from wind uplift or unusual loading, causing truss failure
- CThe truss will no longer meet fire-rating requirements
- DThe top chord will be undersized for the roof snow load
Show answer & explanationAnswer & explanation
Correct answer: B. The unbraced bottom chord can buckle laterally under compression from wind uplift or unusual loading, causing truss failure
Bottom chord lateral bracing is specified by the truss designer to prevent the chord from buckling when it goes into compression, such as under wind uplift or unbalanced loading conditions. Roof sheathing stabilizes the top chord but does nothing for the bottom chord, so omitting the specified bracing leaves it vulnerable to lateral buckling and potential truss collapse.
Why the other options are wrong
- A. Ridge connection issues are unrelated to bottom chord bracing.
- C. Fire rating is unrelated to structural bracing of truss chords.
- D. Top chord sizing is unrelated to bottom chord bracing omission.
Truss Bottom Chord Bracing
Continuous lateral bracing installed on truss bottom chords per the truss designer's drawings to prevent lateral buckling when the chord experiences compression, such as from wind uplift.
- Specified at intervals per truss design drawings (e.g., 10 ft o.c.)
- Prevents buckling of bottom chord under uplift/compression
- Roof sheathing only braces the top chord, not the bottom
Memory trick: 'Top chord's braced by sheathing; bottom chord needs its own bracing.'