Reinforced concrete vs. steel posts

[Environmental_Guy]

Hello out there, I'm an environmental guy for a concrete company and I usually design secondary containment for all of the diesel and hazardous waste storage tanks. My usual design is a reinforced concrete wall around the tank with enough volume to contain the tank and the local jurisdiction usually approves this.

A plan checker has insisted I follow fire code (for vehicle impact) and install 4" concrete filled steel posts for a new tank instead of the usual concrete wall surrounding. She has said that if I can prove the relative strength of the two for equivalent surface areas she'll approve my design. How does one calculate the overturning moment (??) for reinforced concrete vs. steel posts?

Details:

4" concrete filled steel posts, 3' above grade with a footing 3' deep and 15" diamter

vs.

12" thick concrete wall, 3' high, 10"slab, and 18" footing, reinforced w/ #6 rebar @ 12" o.c.

Intuitively it sounds like a no-brainer but she wouldn't buy it. Anyone seen anything like this in any manual?

No need to solve this for me, if someone could just help me out a little, that would be great. If not, no big deal either.

Thanks!

 

[Desert Engineer]

This isn't related to your question. But just out of curiousity, is the purpose of the wall to contain a spill or prevent people from knocking into the tank? Do they want the posts in addtion to the spill containment?

 

[Environmental_Guy]

This isn't related to your question. But just out of curiousity, is the purpose of the wall to contain a spill or prevent people from knocking into the tank? Do they want the posts in addtion to the spill containment?

The posts are for vehicle impact protection, the plan checker is citing Cal Fire Code 8001.11.3 They aren't requiring us to do both wall and posts, but we prefer to build concrete walls, being a concrete company and all. The tank itself, being a double wall, satisfies the secondary containment codes.

This is in Murrieta, CA, by the way. Not too far from you.

As for the original question, I think I am just going to consult with a pro instead.