Thursday, August 25, 2011

Propoane tank anchorage

The building inspectors in the two rural counties (former seismic zone 4 in California) where I work decided that propane tanks needed to be attached to the small concrete slabs that are also required (typically the length of the tank and width by 3" thick)  there is a flexible connection to the gas line- soft copper to the under ground steel pipe. They decided that plastic coated cable over the tank to some bolt or bent rebar embedded in the concrete was an adequate connection. This was enacted 10 years ago. These tanks are for single family homes or businesses. the large tanks the propane company has are 10'x 40 ft and sit in concrete saddles. seem like the should be bolted down.
With the change in concrete anchorage requirements it seems they need to make the tank anchorage meet the new code
I ran a calc for the 250 gallon residential tank per ASCE 7-05 section 15.7.14 horz tank as rigid mass, I got the tank would turn over and slide. I don't have the petroleum codes. I know it could be refined with sloshing and some other assumptions.  But it seem bad to have a propane tank rolling around spewing gas in a seismic event.
I have a past project that in near a small tank farm for a small subdivision it has 8 -500 gallons tank on a concrete slab attached like this. I don't like it. but the propane company has no issues with it.
Any thoughts on this ? What is done in other areas for propane tanks? 
Tim Rudolph PE
Bishop CA