FRP STORAGE TANKS - SEISMIC DESIGN 1

[Jacst3]

Does anyone one know of any standards for design of FRP tanks for the effects of seismic loading? API 650, Appendix E covers the method for welded steel tanks. One can calculate the base shear and overturning moments and thus anchorage. API 12P (Specification for Fiberglass Reinforced Plastic Tanks)does not address the issue.

Has anyone had to deal with this?

Thank you for any information.

jacst3

 

[JedClampett]

Most of this work is done by specialists. I specify the requirements (Sds, Sd1, SG of the contents, etc.), they plug it into their MathCad models and create a calculation. There's four of five guys I've seen that do this for the tank suppliers.
Is there a reason you want to do this, or do you want to just know?

 

[JStephen]

ASCE 7 includes seismic provisions for various non-building structures, and I suppose includes FRP tanks. Note that the R factors may be a lot different from a steel tank.

 

[TLHS]

Jed,

I'm not sure how you specify something if you don't give them guidance on either methodology or requirements for limit states. That would either have to be a reference to a standard or language in your spec that you come up with yourself. Either way, you need to generally understand how a reasonable person would approach the problem. You don't necessarily need to be able to do it, but you need to know the basic process.

If there's no standard and you don't give some further guidance then you're trusting whatever their novel solution may be, or whatever justification they may have come up with as to why they don't need to design to seismic cases.

I guess at a minimum you could use language about being to a similar level of safety and serviceability as provided in whatever other standards exist for other materials. If you just give them a reference to the tank standard, which doesn't have seismic, and throw some seismic values into the spec without clear requirements, you've probably got at least a 50% chance that no seismic design gets done.

 

[FTCTanks]

You could look at AWWA D121-12 that has a whole chapter dedicated to the subject.

 

[Jacst3]

Thanks guys for the response. I have seen straps specified from the manufacturer before for wind and seismic stability. I know that API 650 has seismic design provisions for steel tanks, so I wondered if anyone had seen another API standard covering seismic for FRP - API website was no help.

I have tanks being delivered to a client, both steel and FRP and I wanted to discuss with them the standards that they should be following for proper design.

From what I gather form your responses, when it comes to FRP, the manufacture should have their own engineering department provide adequate design for anchorage, based on their own interpretations of the applicable codes.

 

[JStephen]

The API-650 standard requires the tank to be designed for wind, seismic, etc.
The API-12F and 12D standards are for similar tanks, but don't require any design other than the roof rafters and center column, if any. These standards specify dimensions, thickness, etc., but do not give a basis for general design. Basically, those tanks are treated like if you bought a 55-gallon drum or a bucket where you just buy it and use it and if blows away, you buy another one. Keep in mind, these are intended for oilfield use.

If the API-12P is written the same way, then tanks furnished to it may get furnished in s similar manner, where there's not any wind or seismic design performed. Not to say this is how they SHOULD be furnished, but if nobody requests anything different, then that's what you're likely getting.

As an aside, I heard of one plastic tank being used in North Dakota that blew away, and they finally found it 7 miles from where it had been placed.

 

[TLHS]

I was actually just checking up on some stuff in ASCE 7 yesterday and there is a section for tanks that specifically mentions FRP.

There is a line item in table 15.4-2 for "Flat bottom ground supported tanks: Steel or fibre reinforced plastic". It points you towards section 15.7.

The tank and vessel parts of the seismic section are written to cover the holes in the various specs that don't have seismic considerations in them, or have outdated seismic considerations in them. So it deals with sloshing, and magnifying forces, and additional hoop stresses and things of that sort. Read the commentary as well. It won't help you on the material strength side, but it'll definitely help you on determining the forces and doing the analysis.

I'm assuming API 12P can do the strength side of things, so the two in combination might get you to the right place.