UBC 1997 and API 650 11th Ed. 1

[jramosjr]

I have come across this situation many times lately and I would like to hear your opinion. Most of the designers, when writing specs for steel tanks, use "generic" specs just becasue they are not familar with API 650 or AWWA D100-05 Standards. When specifying the seimic design requirements, all they mention is that it shall be in accordance with the UBC 1997.

As you all know, UBC specifies seismic zones (1, 2, 3 , 4 and 5) while API 650/AWWA D100-05 now specifies seimic use groups (I, II and III). I understand that API and AWWA incorporate by reference the seismic design criteria presented in ASCE 7. However, the criteria presented in ASCE 7 is quite different to that presented in UBC 1997. How are you meeting the requirements of both codes (UBC 1997 and API 650)? The current design code here in Puerto Rico is the UBC 1997. Should I continue designing tanks as per UBC 1997 or should I design them per Appendix E? Which do you think is more strict?

Jorge L. Ramos, Jr., MSCE, PE
Alonso & Carus Iron Works, Inc. (

http://www.alonsocarus.com)

Euro-American Steel Co., Inc. (

http://www.euroamericansteel.com)

 

[IFRs]

Designing to 10 year old codes is bound to give you fits - I'd use API Appendix E if possible.

 

[pmover]

Your question should be directed to your client. Appraise the client of the differences, the advantages/disadvantages, and any cost differences.

Yes, so often individuals that write the specs do not know that conflicts exists between stds. I believe this is simply because they do not know or care to read the stds/ref's. Chances are that you may not get a timely or adequate response from your client.

Short of getting a response from the client, find out which std has precedence and adhere.

My opinion only - me being a cautious individual, choosing the most technically sound choice (less risky) is preferred.

Good Luck!
pmover

 

[IFRs]

Question to the owner: If there is a failure and your tank leaks poison into the groundwater, is your defense going to be "I was told to use a 10 year old code" even though you knew there was a more current code avaialable and accepted by the specific industry?

 

[jramosjr]

Thank you all for your replies. When I present this situation to the owners/designers, the most common response we are getting is "use UBC 1997 requirements." But, my engineeering judgement always tell me to use the the current design standard (API 650 Ed. 11th or AWWA D100-05) and that's waht we have been doing. And anyways, we as tank manufacturers are responsible for the tank design.

Is there any correlation between seismic zones and seismic use groups? I know that there is a correlation table in AWWA D100-05 between occupancy catergories and SUGs.

Jorge L. Ramos, Jr., MSCE, PE
Alonso & Carus Iron Works, Inc. (

http://www.alonsocarus.com)

Euro-American Steel Co., Inc. (

http://www.euroamericansteel.com)

 

[JStephen]

There simply isn't a good answer to the question.

Most of the applications I've dealt with always required the "latest revision" of whatever I was working with. And in some codes, this is required, either by the code itself, or by a replace-this-page updating which effectively destroys your "old" code anytime you update. ASME B&PV is a good example of this.

It was recently pointed out to me in the Structural Forum that in fact most governmental building codes are not set up this way. A city or state will require a specific year of the UBC or IBC codes. That code in turns specifies a specific year of the ASCE 7 and other standards. ASCE 7 then specifies a specific year of AWWA or API standards. But this conflicts with the information included in the standards themselves. So using the latest standard may seem the thing to do, but you could just as easily be asked, "Why didn't you comply with this building code that required the 19xx Standard?" You also lose a couple of years in each reference, so the building code in 2008 will be the IBC from 2005, which requires ASCE 7 from 2002, which requires API from 1999, which references ASTM A36 from 1996, and so on down the line.

In actual practice, I haven't had any trouble with consultants or owners or plan reviewers questioning what version was used for design. It may help to note that API itself specifies when the new standard becomes effective, so anything that requires an older version is automatically contradicted by the standard itself.

 

[gdubyuh]

When I am designing a tank to API-650 that is subject to seismic loading, I will notify the customer of my preference to use App. E with ASCE 7-05 seismic acceleration coefficients, site class, etc. If a client insists on using some other standard (such as UBC 97, IBC, etc), I will design the tank in COMPRESS vessel software (with a flat bottom) and use the requested standard in COMPRESS. I then take the overturning moment obtained in COMPRESS, and substitute that value as the ringwall moment in App. E, and complete the calculations per App. E.