Dear all,
As per B31.3, A302.3.4-(a)Wind and earthquake forces need not be considered as acting concurrently. refer the below load case is the acceptable or not.
1) W+P1+T1
2) W+P1+T2
3) W+P1
4) WW+HP
5) U1
6) U2
7) U3
8) WIN1
9) WIN2
10) D1
11) L1-L3
12) L2-L3
13) L1+L5+L7+L8+L10 Algebraic
14) L1-L5+L7-L8+L10 Algebraic
15) L1+L6+L7+L9+L10 Algebraic
16) L1-L6+L7-L9+L10 Algebraic
17) L5+L6+L7 SRSS
18) L3+L17 Abs
19) L3+L8+L17 Abs
20) L3+L9+L17 Abs
21) 2L10+L11+L12 Abs

For Load case 13 to 16 and 18 to 21. they mention the combination of wind and seismic acceleration.

Is it possible to combine. could you please guide me.

Note:
We are doing pipe stress analysis of FPSO.

Earthquake on an FPSO ?
Do you mean a tsunami ??

hi Moverz,

No. Tsunami and Earthquake. A floating production, storage and offloading (FPSO) unit is a floating vessel used by the offshore oil and gas industry for the processing of hydrocarbons and for storage of oil,

we considered ship acceleration in g's loads in U1,U2 and U3.

I know what an FPSO is, but I am not so sure that an earthquake would have too much effect on a vey large floating mass.

Looking at the normal seismic data for onshore plant, the cyclic response is in the milliseconds area, so I wonder howe a big ship would react to this.

Hi Shabeer,

FPSO required lot of load cases and special attention. Please find the list of load cases required for 1 year wave and 100 wave.may be use full for you.

Regards,

akula

Shabeer,

Ref. my question above, please explain how you intend to model an earthquake on this FPSO.

Hi shabeer,

The U1 , U2 and U3 are acceleration due to wave and nothing to do with seismic activity. The load cases are correct. The code says not to combine wind(gust) and earthquake as these occur occasionally, but the acceleration due to waves are actually operating condition and not occasional.

Regards,

There's no seismic acceleration on FPSO, as Moverz says a Tsunami???. The U's are the vessel acceleration due to wave which is present all the time, the vessel acceleration is considered as operating case, that is why your U is combined with your Wind. Don't be confused between seismic and vessel acceleration, once again there is no seismic loads in FPSO in the first place.

~Clyde