calculating Ca,max in a round pier 1

[joshsd]

I have a wide flange attaching to the top of a circular pier with a base plate and anchor bolts and am struggling to figure out what to use for my Ca,max value.

The base plate is square and the anchor bolts are layed out in a line with 4 on each side of the wide flange. I would like to lay my vertical reinfocing steel out in a symmetric circular pattern around the perimeter. However, I have to keep the reinforcing steel within 0.5hef of the anchor centerline and hef will equal Ca,max/1.5. So, even though I do not need to calculate the breakout strength I still need to find my Ca,max value. Any suggestions?

 

[bones206]

You should use hef as it is defined. i.e. effective depth of the anchor. Ca,max/ 1.5 is a limiting value for the breakout calculation which shouldn't be applied to hef when choosing reinforcement spacing.

 

[civilperson]

Use three each #3 ties at the top 5" of the pier and do not worry about breakout strength.

 

[joshsd]

I should have specified that the load is from a high moment and little shear, so it is the tensile breakout I am referring to. But, I am not worried about the breakout strength just making sure my anchors fall under the 0.5hef per section D.5.2.9.

Bones,

Look at the example 34-8, they used the Ca,max value in this one instead of hef.

 

[Lion06]

hef is what it is. The modification you're referring to is meant only to apply to concrete breakout. If you read D.5.2.3, it says "....the value of hef used in Eq. (d-4) through (D-11) shall be.....". It isn't meant to modify your hef for compliance with D.5.2.9.
That's pretty sweet, having your hands on a copy of PCA Notes for ACI 318-08!

 

[Lion06]

I also want to point out that this example doesn't satisfy the reinforcing being with 0.5(smaller hef). The smaller hef=6", which means the reinforcement should, by your thinking, be no more than 3" from the anchor rod. On page 34-84, when they are calc'ing the req'd length of anchor rod, they assume a 2" cover which puts the outer-most #8 6.5" away from the anchor (9"-2" cover - 0.5"). I would also point out that they conservatively used the distance from anchor to reinforcement as 9" (the actual edge distance), which is again larger than 0.5(smaller hef).

 

[joshsd]

That makes sense to me. I will just go with my standard hef value then and it simplifies a lot.

I also have this, a friend of mine went to a conference and got it, but these two parts are what he sent me that applies to my struggles.