Split Buttress Design
Split Buttress Design
(OP)
We are working on a 20" DIP water main that is being partially being replaced. The main will be cut and capped temporarily while the new pipes are being installed. My manager has asked me to design a split buttress for hold down the pipe during construction. I'm looking for guide on how to design such a thing. My understanding is that it has two concrete blocks on either side of the pipe and beam runs between the two blocks. See the link provided for an example. The county which we are designing this for has standards for up to 8" mains. Any info would be very much appreciated.





RE: Split Buttress Design
A lot of your scan is cut off, but it looks to be appropriate for a much smaller pipe than 20 inch. So all the blocks, embedments, beams, etc. will have to be upsized.
RE: Split Buttress Design
It appears also the designer wants two cross-beams that span across some sort of access plumbing (to the cap etc. for by-pass, filling and/or testing purposes?) It furthermore appears that the designer wants the sort of saddlebag concrete anchors or buttresses on each side to be installed against "undisturbed" soil, in effect thus outside the existing trench. While the forces against a 20" cap will be considerably higher than those against an 8" cap(if that is what is pictured), I have seen this sort of basic thing being done before over the years, and even for quite large pipes and high pressure.
While the publication at http://www.dipra.org/wp-content/uploads/Design-Thr... will probably be helpful in giving you an idea of the kind of force(s) involved, and also the aggregate bearing area of concrete required against undisturbed soil, it will not design this special thing for you. Obviously, the (steel?) cross-beams will also have to be structurally adequate for applied bending and shear forces. I hope this information is helpful.
RE: Split Buttress Design
RE: Split Buttress Design
While maybe not the only way to do this thus (cutting into and?) assembling a dependable bulkhead onto the end of such old pipe will likely require some sort of mechanically-joined cap, or instead a sleeve with plug bolted in to the outside end of same to be slid up over the old cut plain end and then that socket bolted down to the old cut end with a stuffing-box type gasket sealing on the outside of the old pipe.
Of course to be able to comfortably slide something over the cut end of this old pipe and get a gasket to seal, knowledge of the actual outside diameter of the old main where you want to cut as well as the condition of the OD surface where the gasket needs to seal will certainly be good to have. Any chance to make a small >pothole size excavation safely around old pipe to check this out before this buttress work? Once you know plain end dimensions and assuming suitable surface/condition, it is quite possible the old main can be capped (with either modified ductile iron or a custom-fabricated steel coupling closure and the buttress installed
RE: Split Buttress Design
RE: Split Buttress Design
Unfortunately, I don't think "AWWA" really came until a half century or more after your main installation date, so head may not conclusively nail down pipe dimensions - in any case truly interesting testimony that such a large iron main of such high pressure has endured for 162 years. If/when dug up please let us know what you find.