ACI 350-06 Minimum Wall Thickness Requirements

[JMarch]

Hey guys,

Chapter 14.6 Minimum Wall Thickness

I'm designing a 110ft x 45ft x 10ft tall concrete cooling tower basin. Above ground. The owner wants it designed per ACI 350. Hypothetically, if my analysis tells me that an 18" thick wall is sufficient for flexure and shear, do I have to meet the "nor less than 1/30 the least distance between members that supply lateral support" requirement?

That would be 110ft x 0.0333 = 3'-8" thick!

If it was a 60ft long wall, it would require a 2'-0" thick wall! Can I get around this requirement?

I know the answer to this would be buttresses, wingwalls, or pilasters, but I'm trying to get away without them.

Who can help? Thanks.

-JMarch

 

[TXStructural]

I do not have full copy of ACI 350 in my hands, but having looked at the 14.6.1 & .2 provisions, the short answer is "yes". The owner has already said that they want it designed to that criteria, and the minimum is the minimum, so don't try to save money which they feel they need to spend.

If you feel the need, economize elsewhere, by selecting less expensive details, for a quicker build, easier construction, and more durability.

 

[JMarch]

The owner wants to maximize speed of construction and economy I'm exercising due diligence. Out of all of the references I have, this is the only thing that gives a minimum thickness based solely on length of unsupported wall.

-JMarch

 

[hokie66]

110' is a long way to span a wall. Can't you build it as a cantilevered wall?

 

[JMarch]

sorry I left that detail out. yes it is a cantilever wall

-JMarch

 

[JAE]

For a cantilever wall, isn't the "member providing lateral restraint" the base slab?....which is continuous.

 

[hokie66]

JAE is correct, of course. A cantilevered wall could be miles long, and the thickness required would be unrelated to the length.

 

[JMarch]

It was unclear to me, that's why I consulted the experts here. I see now in section 14.1.2 where it says "Cantilever retaining walls are designed according to flexural design provisions of Chapter 10..."

Thanks all for your input.

-JMarch