RAM SS Pile Cap Design Question

[AtlAC]

I'm using RAM SS to design some pile caps. We are able to use just a 2 pile orientation with overall dimensions of 4.5'x9'. The program seems to giving output for the reinforcement in the long direction that is using the loads and meets minimum requirements per ACI 318. However, in the short direction the program is saying no steel is required. I'm at a loss as to why RAM SS would not check minimum steel requirements in the short (minor) direction. If anyone has ever dealt with this before, I would greatly appreciate any information regarding to what the program is doing.

 

[dik]

Is the steel in the short direction for distribution of loading?

Is the element small enough that temperature or shrinkage issues are not a problem?

Is the element thick enough that it could be considered as 'mass concrete'?

Irrespective of the program's output, is this a discretionary issue for the engineer?

Dik

 

[AtlAC]

The Pile Caps are 4.5'x9' with a thickness ranging from 2' to 2'-10" thick. Based on CRSI it says to use ACI 7.12 and 10.5 for minimum reinforcement in pile cap foundations.

 

[dik]

Is it a requirement to use the ACI recommendations... or only that CRSI suggests it (position may be indefensible in court)? They are in the business of selling rebar.

Dimensions are small enough that shrinkage may not be an issue... doesn't qualify as mass concrete but there would be some heat generated.

Dik

 

[AtlAC]

That's kinda what I'm trying to figure out what other Engineers do in pile caps and if anyone has run into this situation in 2 pile orientations where from a pure load perspective only bars in the long direction are required.

 

[dik]

Current practice for pilecaps is to use a 'Strut and Tie approach' If designed as a flexural item, then I've often used a few stirrups to support the top bars and keep everything in place; I've never considered temperature reinforcing as a criteria.

Don't know what anyone else does... but suspect many use S&T method. It seems to be trendy.

Dik

 

[structSU10]

As long as you have some kind of element on top of the pile cap (grade beam maybe) to handle any moment from tolerance of piles / pile cap location in the short direction, then you can probably get away with it. If you don't, then you need to develop a torsion in the pile cap and moment in the top of the piles.

 

[sticksandtriangles]

I've been designing pile caps via strut and tie.
Pretty quick to do in simple cases, but can get complicated quickly.

 

[SethGuthrie]

Ram Foundation uses a beam flexure approach for pile cap bending design. The demand is derived from the pile reactions and hence, in the 2-pile cap we are only looking at behavior in one direction. It does not use the strut and tie method which would probably better for thick caps.

 

[KootK]

The only strength demand for transverse reinforcement that I'm aware of would come from this kind of thing for caps designed by strut and tie. You know, other than conventional shear and torsional rreinforcing ties.

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.