Dear Mr. Delaforce,

To comment the original question, it was one of Open-Ended category.
"My question is how to compute Gx & Gy acceleration based on seismic zone and applicable parameter."

Even it wasn't my question, I do not understand the answer so I'd like to comment it.

First about the sentence "Just enter reasonable values for Gx and Gz and you will get a simple result." I can say that acting as a Client representative I would reject a calculation based on such approach. Using software and "just" feeding software with numbers as input is the modern "plague" in engineering. It is the Software user responsibility for the input values. A part of the responsibility is proved by the user explaining the input values.

Second, what Rajendra said is the fact Software warned that applying a building code [which assumes that all of the mass is located above the point of support] makes its use on lug supported vessels questionable. I think the warning is correct in intentions, however I would be not so convinced that the root of the problem is the mass distribution vs. supporting point. May be the rigidity of the legs vs. vessel, as well. In my opinion what I need to know better is the first mode of vibration and the relationship with the seismic spectrum- mass distribution, rigidity of components, etc- all have consequences here.

Third, you mentioned 0.4G as quite conservative and probably thought as reasonable conservative. It is reasonable as ground peak acceleration and the vessel will "see" such acceleration in case has a quite rigid behavior. It is not reasonable in case has enough flexible behavior and the vessel would be subject to the maximum value of the design spectrum acceleration, which can be 2.5 to 3 times the peak ground acceleration.

And last- your advice was to not worry about the R value when calculation a vessel. An R=1 value means the calculation is developed in the elastic domain. A value of R=2 for example is currently associated with inelasticity based on structure ductility.
Here I have an open question: what exactly we accept as inelastic behavior when adopting such value for a vessel calculation?

Thank you and best regards.