huangyhg

round tube / pipe moment splice
i'm currently doing research for a project that will require several moment splice connections for round steel tube / pipe sections. each splice will also contain a reduction in the diameter of the next pipe section. the project is a tall spire (200'+) and i am proposing to design it similarly to a steel stack vessel. i've already found a good reference (ansi/asme sts-1-2006), but have yet to order.
anticipating that this reference does not include the design of the connection i've mentioned, i was hoping to see if any of you knew of any good references. i have conceptually laid out the connection (see attached file) and have some ideas on how to analyze, but am looking for some back up material to make sure i'm covering all bases.

the drawing looks like you are planning on using bolted connections. assuming that each pipe is long and has a relatively small diameter, the bolt head (or the nut) inside the larger pipe is not accessible for tightening during assembly.
if this is true, perhaps tapped holes, nuts welded inside, etc. could be a solution.
actually, the diameter is large enough to allow an internal ladder for maintenance at the top of the stack. so internal bolting of the flange is an option. each section is 40' long (for shipping) and diameters range from 72" to 42". welded nuts would be a good idea though...
there is a body of opinion that high strength nuts should not be welded, even for this purpose. there is a current thread around somewhere about that.
is the spire to be ground mounted or on a building? if on a building, i would research oscillation initiated failures. i can't really give you any details, other than to say i have read about problems with antennas, spires, etc. on tall buildings.
the welding of the flanges to the pipe sections should be complete penetration, which would probably best be done from outside with backing bars inside.
i have seen similar spires made tapered rather than stepped. don't know how they do it, but would avoid stress concentrations.
what about a round plate with smaller pipe diameter inserts (to be used as backing for the welding) that are welded to the plate... these inserts could be long enough to have holes for temporary thru-bolts for the in field welding alignment of the pieces.
mike mccann
mmc engineering

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