Conc. Wall or Column? 2

[jechols]

I have a series of 32"x8" concrete columns at about 12' on center. Several have 200+ kips (factored axial load) on them. I was planning to treat them as columns and provide confined reinforcement but some other engineers in my office say the columns are actually wall segments and can be designed using the empirical equation 14-1 ACI 318 which means only minimum reinforcing is required. Wall or columns? I cannot find a definition for a wall other than:

Member, usually vertical, used to enclose or separate spaces.

and using the column definition everything is a column.

Thanks for any input

 

[MotorCity]

I do not have the code in front of me, but I would not be comfortable with designing members carrying +200k using an empirical approach. Just my 2 cents.

 

[jechols]

The empirical equation yields a very high capacity and empirical equations are usually conservative if you meet all of the criteria, correct?

For my situation phi*Pnw= 0.55*.70*4000*32*8[1-(1.0*144/32/8)^2]= 269.5 kips

This is more than enough.

 

[UcfSE]

Is your resultant within the middle third, does it include moment magnification and/or minimum design moment? I suppose if you meet all the criteria then it is your decision but I personally wouldn't feel comfortable with a large load being supported on unconfined concrete, especially if you are in a seismic region. That's just my opinion though.

 

[aggman]

As long as you are meeting the criteria for the empirical design, and seismic is not an issue than I can not see any reason to go crazy with the reinforcement. A 32" x 8" column with 1% As and no bending is good for:

phi@Pn,max = .80*.65*[.85*4000(256-2.56)+(60000*2.56)
= 528 kips >>>= 200 kips.

This is a great deal more capacity than is required and you will be adding a lot of unwarrented labor. If you have concerns then require the wall detail to use closed ties instead of just horizontal bars. This will give some confinement.

 

[MotorCity]

I agree with the above posts. As a matter of personal preference, I try to avoid using empirical design whenever possible. Depending what seismic zone you are in, empirical design may not be allowed.

 

[14159]

If you do treat them as walls, you should design them for the design load, moments, and unbraced lengths because 8-inches is not very thick. I don't think that the empirical methods include slenderness, but might be wrong. Like others, I avoid the empirical method. PCACol is one example of a program that makes complete inclusion of slenderness, etc very simple and fast. I just don't see a reason to do something half-way when it's so easy to do it right.

You should try to find out what precast manufacturers do for their lite walls. That's the best comparison that I can think of.

Also, you could contact ACI for an opinion. They are pretty good at answering questions like this.

I would not use them unconfined until I found out more about this stuff.

DBD

 

[jechols]

I have decided to treat it as column. Thanks everyone for your input