Truss/Joist End Moments
Truss/Joist End Moments
(OP)
I am currently designing an expansion to an existing steel-framed building. The existing building is framed with trusses in both orthogonal directions and are moment frames.
The original engineering drawings specify end moments for the truss connection design, the drawings state that these moments are due to lateral loads only. The connections of the chords to the column are standard WT bolted/welded to the columns.
What is throwing me off is: how can the end moments not include moments due live or snow loads? I imagine that these moments would be higher than those created by lateral loads.
When specifying joist rigid frames (joist design being by specialty engineer), I have always provided a table that shows moments due to snow, live, wind, and seismic.
Your thoughts are appreciated.
The original engineering drawings specify end moments for the truss connection design, the drawings state that these moments are due to lateral loads only. The connections of the chords to the column are standard WT bolted/welded to the columns.
What is throwing me off is: how can the end moments not include moments due live or snow loads? I imagine that these moments would be higher than those created by lateral loads.
When specifying joist rigid frames (joist design being by specialty engineer), I have always provided a table that shows moments due to snow, live, wind, and seismic.
Your thoughts are appreciated.






RE: Truss/Joist End Moments
RE: Truss/Joist End Moments
RE: Truss/Joist End Moments
I've run into a few of these myself. My thoughts:
1) Truly, it's probably an oversight.
2) It might be mitigated somewhat by the potential to lock in the bottom chord connection after much of the dead load is in place.
3) Designers may have been attempting something like the partially restrained moment frame system that we sometimes use with steel beams. It may not have been justified but may have been the intent none the less.
How old is the existing building?
I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.
RE: Truss/Joist End Moments
RE: your second para., “the drawings state that these moments are due to lateral loads only.” Mightn’t this be interpreted to mean, that these are the lateral load frame moments, and that the truss designer should add these to the other loads/moments caused by the various other loads which they would apply to design their joists and trusses? These ‘other loads’ would be dictated by the AHJ/local codes and likely be shown in the structural general notes too. Do a rough check of the ends of the trusses/truss chords and connections to see if they would actually carry the total load reactions and moments. With a few notes and tabulations the original engineer could have been much more clear about their intentions.
RE: Truss/Joist End Moments
RE: Truss/Joist End Moments