Footing Piers Cracking Region for Anchor Bolts? 3

[waytsh]

Referring the ACI 318 Appedix D - Section D.5.2.6. Would a properly reinforced footing pier need to be considered a region that is likely to crack? I know the examples shown in the PCA notes show that this should be the case, but I think they are working off the assumption that there is no reinforcing in the pier.

Just wondering whether everyone else is using the 1.0 or 1.25 adjustment factor for this condition with cast in place anchors and reinforced pier.

Thanks,

 

[dik]

You should check the pier and the development length of the reinforcing and anchor rods.

Dik

 

[waytsh]

My thought was that since the anchor bolts are extending down into the pier stirrups they would be more confined than in plain concrete and I could perhaps use the 1.25 factor.

 

[dik]

If pier reinforcing has a greater area than the anchor rods, you should still check for splice length... If the first tie is say 3" from the top, it is possible for the anchor rods to pull the tie and the blob of concrete off the pier vertical reinforcing. The tie, can offer no resistance whatsoever if it gets pulled off in the block of concrete...

Dik

 

[miecz]

See the article on page 39 in the July 2004 issue of Structure Magazine for a practicle approach to this problem.

 

[jt12]

I believe all testing backing up app D was done with concrete unreinforced, so that shouldn't matter. I'd think if you calculated your stresses and they were all less than rupture stress then you could use the 1.25 factor

 

[waytsh]

Thank you all for the input. I did find the article from Structure. I must have missed it somehow on my first search throught the threads. It was very helpful. I plan to use some of the techniques mentioned.

 

[waytsh]

Getting off the subject slightly, what is the c a,max term exactly when you are on a pier? Is it the distance from the center of the anchor bolt to the furtherest of any of the four sides or is it the greater of ca1 and ca2?

 

[miecz]

According to the commentary to RD5.2.3, Cmax is the largest of the edge distances that are less than or equal to 1.5hef. Under D.1, Edge Distance is defined as the distance from the edge of the concrete surface to the center of the nearest anchor. So, it would seem that cmax is the greater of c1 and c2.