expansion in HSS truss
expansion in HSS truss
(OP)
I'm designing a welded square HSS truss pipe support that is approximately 450 feet long with HSS column supports at approximately 80 feet on center. The client has insisted on using tubes because they do not want birds nesting in or on the structure. However, the truss is outside and it will be exposed to maximum 110 degree F and minimum -30 degree F temps. Since it is so long, I think I need to allow for expansion in the truss bottom and top chords. Does anyone know of a good connection detail at the column supports that allows for expansion? Any help is greatly appreciated. When I mentioned this issue to my supervisor, the only thing he said was, "yes, this is something you need to consider"....not much help. Is there anything else I could be missing??






RE: expansion in HSS truss
RE: expansion in HSS truss
RE: expansion in HSS truss
RE: expansion in HSS truss
RE: expansion in HSS truss
RE: expansion in HSS truss
RE: expansion in HSS truss
Is that what the expansion is if I allow for it at each support at 80 feet on center, or if I do what civilperson suggests?
RE: expansion in HSS truss
RE: expansion in HSS truss
This will tilt the column and result in a lateral component to the column loads (easily calculated by vector geometry).
Then you just need to ensure that your truss can take this additional load.
csd
RE: expansion in HSS truss
RE: expansion in HSS truss
as per the OP it is 140 degree change. I assumed worst case using the AISC tabulated values.
csd
RE: expansion in HSS truss
RE: expansion in HSS truss
RE: expansion in HSS truss
RE: expansion in HSS truss
RE: expansion in HSS truss
RE: expansion in HSS truss
RE: expansion in HSS truss
RE: expansion in HSS truss
RE: expansion in HSS truss
RE: expansion in HSS truss
Back to my previous post, I am wrong about simple spans meaning you need twice as many slide bearings. You would only need to allow for movement on one end.
RE: expansion in HSS truss
RE: expansion in HSS truss
I'm a bit confused now... you are recommending that I don't need to do the slide connections, and that the tilt is actually very small in the columns? What would you do differently to the base of the column to allow for more tilt? And why is it important to make the truss continuous over the top of the column? Could I just do a standard pinned connection?
hokie66 - Could you tell me some of the problems horizontally slotted holes have when under gravity loads?
RE: expansion in HSS truss
Not sure off hand what you could do to allow for even more movement if the columns and bases cannot combine to allow for the needed movement, outside of a sliding interface.
Standard pinned connection at the top of the columns are fine. Civilperson will probably correct me if I'm wrong, but I believe the comment about continuity was in regards to the thermal expansion (in other words, sliding bearings may not be needed).
What sort of bearing are you dealing with at the piers? I often see pipe bridges requiring elastomeric bearing pads etc. at each pier (thought that's with 200' spans). If a sliding surface is needed, the details may depend on any bearing requirements.
RE: expansion in HSS truss
RE: expansion in HSS truss
The rotation required would be a very small fraction of an inch.
csd