Seismic provision is rewrited in API 650 11th Edition. Until 11th edition, the seismic provision of API 650 was based on Uniform Building Code (UBC). In 11th edition, API changed their mind accordign to American Society of Civil Engineer (ASCE). New seismic provision is based on Minimum Design Loads for Buildings and Other Structures (ASEC 7-05).

This was the big change! Because all of calcutaions was changed. But, I think the most important cahnges that data inputs were changed. All our customers are still get their seismic information us as per UBC-97 data. Unfortunately, ASCE 7-05 inputs are different than UBC. What shall we do? We must convert these UBC input datas to ASCE data. Here is the solution steps:

1. Calculate fundamental vibration figure of storage tank considering roof, roof structures, appertunances etc.
2. Ca, Cv, Nv figures read form tables 16-Q, 16-R and 16-T of UBC-97 accordingly.
3. Calculate Sp figure using with Eq.30-4, Eq.30-5, Eq.34-2, Eq.34-3 of UBC-97.
4. Select Sp figure.

After that we use Sp figure in seismic provision of API-650. This post is an idea that how you can convert UBC seismic data to ASCE. I hope it is usefull for you.

The buckling behaviour of shells is not widely known and simple procedures for analysis of buckling of shells are avaliable only to a very limited extent in design codes. Although AWWA D100 considers the buckling effects in itself, API 650 doesn't investigate any buckling behaviour of shell structure.

Storage tank designers must be consider the buckling behaviour due to self weight, vacuum load, wind load and seismic load effects on shell. At the present time, several papers or standars are avaliable :

• Det Norske Veritas: DNV-RP-C202 : Buckling Strength of Shells
• DIN 1880 Part 4: Structural Steelwork Analysis of Safety Against Buckling of Shells
• ASME Code Case N-284: Metal Containment Shell Buckling Design Methods, Miller C.D. 1991,

In my oppinion, DIN 1880 Part 4 has more practical solutions instead of others.

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