Strut and Tie with Drilled Piers

[ron9876]

My condition is a grade beam (6'x6' beam)that spans an underground pipe. It has a 30"x30" column at the top and 60" diameter drilled piers at the ends. The design examples that I find determine the dimensions of the nodes and related struts based on the applied loads and allowable stresses. However, when this doesn't work for the applied loads, it seems reasonable to me to assume that the node bearing area could be the equivalent square of the drilled pier at one end. This means that the strut dimensions will vary along it's length. Does this approach make any sense to anyone else. To decide that the condition doesn't work because you use a 30" wide strut at lower node doesn't seem reasonable to me.

Also, based on ACI318, to use the strut strength based on section A.3.3 wouldn't you need reinforcement parallel to the face (side bars), vertical (ties) and perpendicular to the face to reinforce the bottle shaped strut in both directions?

Thanks

 

[KootK]

Certainly, I agree that you don't need to consider only a 30" wide node at a 60" pier. That said, your node directly below the 30"x30" column needs to work.

And yeah, by the book you do need crack control reinforcement. It's pretty common to ignore that for pile caps for some reason. We discussed that recently here.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.