asce 7-02

[gwn]

Question related to calculated seismic forces for cylindrical, flat bottom vertical tank. Tank is anchored at grade.
Per asce 7-02, table 9.14.5.1.1; R = 3.0 for steel tanks.
Can I use R = 3.0 for fiberglass (FRP) tanks?

 

[JAE]

I'm looking at the 7-02 table you reference and I see the type indicated as "All other self-supporting structures, tanks, or vessels not covered above or by approved standards that are similar to buildings." R = 1.25.

I would think you'd use that.

 

[aggman]

I would use R = 1.5. This is for flat bottom ground supported tanks or vessels using "other material". (Same table, same location, at bottom of section.

 

[rd78]

The R value of 1.25 is probably the strictest reading of the table although a case could be made for 1.5 "Tanks with unanchored and unconstrained flexible base". Intuitively however, fiberglass would seem to be closer to steel in terms of flexibility, ductility, etc. and using the conservative values based on "other materials" might be a severe penalty.

Having faced this issue a year or so ago, the research led to the 2003 NEHRP (Chapt 14) which specifically lists fiberglass in the table. (I hope I remembered the reference right). The R value in that document is 3.0.

Good luck.

rd78

 

[JAE]

rd78 - good find on the NEHRP table.

 

[JStephen]

I believe "unconstrained flexible base" is referring to a concrete tank where the tank shell simply sits on the floor slab- the floor isn't connected to the slab, if I understand it right. I assume the fiberglass tank shell is connected to the floor.