Pressure Vessel Design for Seismic Loading

[solerpanel]

Hello,

This is my first post on eng-tips. I hope there is someone out there with experiance in PV design for seismic loads. Here goes...

I am doing some work with seismic design for water storage tanks. Nothing too fancy, horizontal and vertical vessels. I have the Pressure Vessel Design Manual from Dennis Moss (Ive heard mixed reviews about this text). The question I have is as follows.

The determination of the seismic loading value is based on geographical location of the pressure vessel. This location will be in a seismic risk zone identified by a map from the UBC. Using the UBC methods, the seismic design loads are developed. The loading is determined as a fraction of the operating weight of the vessel. The ratio of the design load over the vessel weight is equal to the ratio of the ground acceleration to the acceleration of gravity.

The ground acceleration value determined by the UBC is far less than the potential ground accelerations identified by the IBC/USGS hazard maps. Does anyone definitevly understand why?

Is the UBC method still in practice?

My apologies for the long question. Any technical insight would be appretiated.

Many Thanks

 

[weab]

If the tank is in the United States, then you should probably be using the applicable code of that jurisdiction, usually IBC latest edition. IBC is more precise, I would think higher or lower loads depending on specific location.

If you are comparing to UBC94, then yes UBC94 loads are much lower because they are at service levels. Starting with UBC97, ultimate seismic load is calculated and should not be factored.

 

[IFRs]

The siesmic maps are now done by zip code. I use

http://earthquake.usgs.gov/research/hazmaps/design/.

Definitely get the applicable code - maybe AWWA D100-05?

 

[MJCronin]

I suggest that you stay away from the Pressure Vessel Methods in the Moss text if you have a flat bottomed tank.

There is an appendix to API-650 which addresses seismic design.

There is also a chapter in the "Storage Tank Handbook" which talks about seismic design for flat bottomed tanks