Seismic Response factor (R) for supporting structure of a horizontal vessel

[afmunene]

The guy who review our engineering, told me that we have to use a response factor R = 2, for the structure in the subject in this forum. I think this is very conservative, because the vessel is supported by steel structure at ground level upon a slab that supports the whole thing (equipment and structure). He is taking into acount the table 4.C.1, point 2.0 of the "ASCE Guidelines for Seismic Evaluation and Design of Petrochemical Facilities". There is clearly shown that if T < 0.06 s, you can use R = 3; other way, you have to use R = 2. In staad I model the vessel to obtain T (with the Rayleigh tool), but of course, software gave me what I do not want, that is T > 0.06.

The question is easy: Can I demonstrate him that is rigid to use R = 3? How can I do that?

 

[SAIL3]

The vessel itself probably is rigid, but the support stl which you have not described may not be rigid....

 

[JoshPlumSE]

I'm looking at Table 15.4.2 of ASCE7-10 and I'd say this sounds like it is probably a "Horizontal, saddle supported welded steel vessel" with R = 3.

If you consider it to be an "elevated tank on unbraced legs or asymmetrically braced legs" then it could be R=2