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Concrete saddle

Concrete saddle

Concrete saddle


Could you provide reference to design concrete saddles in lieu of steel saddles for horizontal vessel.Can we use Zick method?


RE: Concrete saddle

"Can you use the Zick method?"  Yes but it may be better to try other groups that use concrete saddles all the time, namely the water industry for above ground pipelines.

Start with my answers in thread378-133164 (self supporting steel pipe) in the 'piping & fluid mechanics' forum.

Books are: -
Bednar - pressure vessels.  Good with lots if info, but a lot of work to find your specific case.

AWWA M11(American Water Works Assn manual M11) steel pipe design & installation.  Good, but use the latest edition (2004 I think).  There are still some errors even in this latest edition (see my thread answer above).

ASCE 79.  Good publication but expensive for a 'one off' design.  AWWA M11 will be better even though a little conservative.

Troitsky steel tube design.  Good sections on both above & below ground pipes.


RE: Concrete saddle

I just re read your request.  Design of concrete saddles usually use an included angle of 120 to 180 degrees.  Stresses at the saddle tips are lower for a greater angle but usually 150 degrees is a max because an empty pipe that has a saddle cast around it, will lift off the saddle tip on pressurisation, so 150 is the most effective angle that you can achieve in practice.

The saddle dimension (parallel to the axis of the pipe - or pressure vessel) does not influence the saddle tip stresses (see Roark & Young - formulae for stress & strain), so saddle lengths of 300 mm are OK even for large pipes.  Make sure that you adequately reinforce the horns of the saddle (see ASCE 79 for more info).  They act like small cantilevers subject to loads from the pipe pressurisation.


RE: Concrete saddle

Classic Zick method does not actually design the saddles to my knowledge, rather it analyzes stresses in the shell, due to weight acting on the saddles.

Another means would be necessary for the saddles themselves.


RE: Concrete saddle

Team Member

Mr. L.P. Zick, Director of Engineering, CB&I in 1940's

The L P Zick paper see the following link:

 The L P Zick paper for horizontal vessels on saddles

RE: Concrete saddle

The classic Zick method does however give you the loads applied to the saddles, which are what you need to analyze them.

RE: Concrete saddle

For design of a vessel supported on concrete saddles the Zick analysis can be used to determine stresses in the shell. The Zick paper discusses this issue. The same equations are applied to both concrete and metal saddles.

I guess this begs the question of whether there *should* be a difference in the equations. The load transfer to the saddle will be different for a vessel that is welded to the shell than if the vessel is loosely sitting in the saddle.

RE: Concrete saddle

"Can we use Zick method?"

Of course! At least for evaluating the stresses in the shell. The question I've been asking for a while (with no satisfactory answer yet...) is, as alluded by Tom Barsh, "Can the Zick method be used for steel saddles welded to the shells?" After all, Zick based his study on steel vessels on concrete saddles! Why do you think those plates are called "wear plates" and not "reinforcing pads"? I've yet to see a solid justification for using Zick for welded on steel saddles. The only reasons I can come up with are 1) We (industry) have not had significant failures whith this approach; and 2) There is no alternate method short of FEA. (Yes, Leonard, I know Paulin can handle this, but I don't use his software...)


RE: Concrete saddle

To jte, I think that both of your answers are correct.

Roark & Young (formula for stress & strain) has a method but it does not include the stiffening effect of the steel shell when pressurised.

ASCE79 (power penstocks) uses an approach based on ASME.  The formular is the same as in Bednar (pressure vessels).

AWWA M11 (steel pipe design & installation) uses a simpler approach with essentially the same result (calculations are simpler).  This is based on work by Stokes of South Australia & published in the Transactions of the Institution of Engineers Australia in 1965.  Stokes developed a method of analysis & verified the work with models.  I do not know if the ASME method has been verified with model tests.


RE: Concrete saddle


I do not know why you would ever prefer conrete saddles ove welded steel saddles for new construction. I would imagine that they would be more expensive and potentially troublesome.

Using the Zick methodology for the evaluation of existing concrete saddles in one thing.

Concrete saddles have the potential for concentration of the load on the inside edge of the saddle, as the vesssel is filled (the inside edge is the one closest to the vertical vessel centerline). Welded steel saddles deflect and distribute the load to the shell of the vessel.

Weleded steel saddles are inspected in the shop..... conrete saddles ....who knows

Anyone out there have any bad stories to share ?


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