What method of analysis is used to validate an offshore vessel is structurally sound?

[JoshRanch]

Howdie Structurally inclined friends.

We are replacing an offshore separator, and our client wants us to run some type of additional structural analysis using their measured spectral accelerations.

As is, we are accustomed to using ASCE-7 and our software Compress is set up for this. This code is also referred to in section 8 as well, but this validation is outside of that scope.

They supplied spectral accelerations measured at the platform level the vessel is intended for install. Our team is mechanical, with 2 AI's and they have not been able to provide a direct response.

 

[JStephen]

I haven't used Compress, so I don't know what all the capabilities are. But you should be able to use the seismic design aspects for their accelerations.
Normal seismic design calculates an elastic response, then divides by R to account for inelastic action and limited damage, and depending on the details of their accelerations, you may need to use lower R values.
Typical seismic values are based on a specific period of return expected, and if that is different from their spectrum, you'd need to adjust for that.
If the separator is small enough and stiff enough to be considered as "rigid", that will simplify things considerably.

 

[phamENG]

When you say 'offshore vessel' are you referring to something on a ship?

If so, I think you need to consult with a naval architect experienced in this sort of an analysis. Most of us are building structural engineers, and while some of the basic theory may apply the methods we use practice aren't going to line up.

I'd be hesitant to use seismic relationships...the behavior of a building structure in an earthquake is relatively well understood and specific. The accelerations you're looking at are likely to be very different than an earthquake and it may be unconservative to try to swap them out.

 

[JStephen]

I assumed "vessel" as in Pressure Vessel per ASME Boiler and Pressure Vessel Code, Section VIII.
And I assumed "offshore" as in oil/drilling platform.
Assuming pressure vessel, it would likely fall under the "non-building structures not similar to buildings" in ASCE 7. So most of the building behavior is not applicable.

 

[phamENG]

If the accelerations are seismically induced, then yes. But any other source and I'd be very hesitant to assume they're compatible without a thorough investigation into their source and how they compare with seismic accelerations.

 

[HTURKAK]

We are replacing an offshore separator, and our client wants us to run some type of additional structural analysis using their measured spectral accelerations.
As is, we are accustomed to using ASCE-7 and our software Compress is set up for this. This code is also referred to in section 8 as well, but this validation is outside of that scope.
They supplied spectral accelerations measured at the platform level the vessel is intended for install. Our team is mechanical, with 2 AI's and they have not been able to provide a direct response.

I understand that the vessel is oil seperator ( probably skid mounted Hydrocyclone for fixed offshore platform ) at platform level.
If this is correct, you can follow ASCE 7-16 section 15.3 NONBUILDING STRUCTURES SUPPORTED BY OTHER STRUCTURE, and 15.3.1 adresses 13.1.6
Good Luck!