A preferred format for foundation loads for pressure vessels and similar structures? 1

[TomBarsh]

For engineers designing foundations for industrial equipment such as pressure vessels, storage bins, etc. what would be the preferred format for receiving foundation loadings? Would it be preferable to be given un-factored loads? Would it be preferable to be given factored load combinations as per the applicable standard (ASCE 7, IBC, some people are still using UBC, and then there's NBC-Canada, and standards from other countries, etc.)?

For a skirt-supported structure I'm sure that it's best to be given the overturning moment acting at the elevation at bottom of the skirt base ring. But what about for structures supported on individual "legs" or columns? Should "loads" (forces and moments) be given at the base of each column? or should the loads acting on the entire structure at the bottom plane be provided?

Thanks for your inputs!

 

[TLHS]

Perfect world, I'd get overall external loads and also reactions at each support point.

The former makes it clear that you're hitting all the loads for your overall foundation design. Trying to back calculate a foundation load from a series of reactions at several connection points can be hell because the sum of your worst case reactions at each support point doesn't necessarily equal your worst case overturning case, for instance.

Reactions at each support point is important, because it means you don't have to assume how the product designer expects the loads to distribute. If you get *just* the overall loading on the structure you can reasonably easily come up with some sort of connection forces, but they may not be the same load distribution that the product designer expected. It can depend on the stiffness of the components of the tank, so it's better if this comes from the vendor.

As far as factored or unfactored, I would prefer factored but I would generally include how I want it to be factored in the spec. As far as what provides the most information, it's likely unfactored loads separated by type (Live, Dead, Wind, Seismic) at each point.

 

[Once20036]

I would expect the loads to be given at the point where one engineer's responsibility ends and another's begins. If the equipment manufacturer is expecting the legs to be provided by others, the load at the top of the legs would be most appropriate. If the legs are integral to the equipment, loads at the base of the legs.

For something supports on a continuous skirt, I`m accustomed to the manufacturer giving the total load, overturning and shear under wind load, overturning and shear under seismic, and the worst case tension reaction based on the number/spacing of the anchors they select.

I typically prefer unfactored loads. If factored loads are provided I believe they need also need to provide a list of the load combinations used. Load combinations between disciplines may not be identical.

 

[TomBarsh]

Thank you for the comments and insights. They are appreciated.

Can anyone else add their insights as well?

The purpose for this is that I am trying to come up with a standardized format for foundation loads for this type of industrial equipment, to be produced by a software application. Thank you.

 

[JStephen]

Some of the loads that come up don't have specific load factors included in the building codes, and some load combinations vary for oddball items. I think it would be best to give unfactored loads with indications of how the loads are to be combined.
Examples:
Internal pressure on a tank shell, or test pressure, or failure pressure or venting overpressure or pressure combined with wind or seismic.
Weight of material added as corrosion allowance.
For tanks and larger vessels, most of the seismic loading is due to the tank contents, so the seismic load that would normally be considered is seismic + contents, and the weight resisting overturning would also include the contents where applicable.

 

[sundale]

I would like the loads given in the nomenclature per Process Industry Practices (PIP) STC10105 - Structural Design Criteria, i.e. Empty Dead Load = De, Test Dead Load = Dt, Operating Dead Load = Do, etc. I prefer service level forces, except now wind and seismic are ultimate forces. PIP has some slightly different load combinations than those prescribed in ASCE 7.