Seismic Design - Pressure Vessels -Chemical Plants

[condesinc]

Am looking for guidance on treatment of seismic loads for pressure vessels. Our application: Polyester Chemical Plants.

Up to now, we have just been using a "g" load of .06/.07 corresponding to Mercalli scale of VI. A new client is in a zone VIII, which gives a horizontal g of .25/.3 to use.

The problem: Client has come back and said a soil factor of 1.5 is applicable. Our vessel expert in India says we do NOT have to apply this factor to the basic g loading, this is for civil structural only. I think he is wrong.

Further complication: much of the equipment is not at ground level but at elevated levels in a large re-inforced concrete building.

Am looking for: Does multiplier apply or not and any other words of wisdom, listing of good references without spending a fortune, understanding of why softer soils gives a higher soil multiplyer, and exactly why the multiplier comes into play; ie, is the acceleration actually higher, etc.

Any assistance would be most appreciated

 

[MJCronin]

I suggest that you re-post this question on the structural engineers forum....you will get a lot more people with experience in the use of seismic soil factors.

Boiler and pressure vessel people are more involved with the subtleties in the design of components rather than the definition of loadings,

My experience with seismic analysis of equipment located within concrete/steel structures was in the nuclear power plant design business....in the 1980s.

The structural group would define "amplified response spectra" to be used in the analysis of piping and equipment contained within the buildings. The spectra represented the eartquake loading as seen by the equipment

Hope that this helps....


MJC

 

[prex]

I agree with MJC on reposting this on the structural forum.
Anyway ASCE 7 has rules for calculating lateral forces on elements of structures and nonstructural components, but of course this is not necessarily applicable in India. An importance (not soil) factor of 1.5 is provided for equipment required for life safety systems or if the plant is classified as an essential facility (what is likely to be).

prex

http://www.xcalcs.com

Online tools for structural design

 

[DSB123]

codesinc,
MJC is correct. If your equipment is located in a structure/building then it's response to an earthquake must be considered. The structural guy's should provide you with a modified response spectra dependant upon the level of the equipment within the structure.