Rebar Layout

[SemiPE]

For pile caps with three piles (3 piles forming a triangle, column on center), designed using strut-tie method or truss method, aren't the rebars supposedly parallel to the 3 tension chords of the strut-tie/truss model? which in this case would form a triangular shape on plan.

However, on most drawings that I have seen, the rebars arent laid out in this manner. The rebars are often laid parallel to the plan orthogonal axis (Horizontal and vertical axis at right angles). I know it is more practical, but isn't this an incorrect way of laying out the rebars for the tension chord? I dont think that the 2 tension chords, oriented at 60 deg on plan (the third tension chord being parallel with the x-axis) could be converted to an equivalent x & y tension chord.

anyone care to help me on this

 

[BUGGAR]

I've always seen the main reinforcing in three-pile caps oriented in a triangle above the piles, including and especially shear reinforcing. Secondary reinforcing (the "just because" steel) is frequently on an ortho grid.

In these situations, headed dowels in the piles are a good way to go.

Bob

 

[SemiPE]

Hi Buggar, Thanks for your reply. May be it is a regional thing. I haven't seen a drawing showing a triangular lay out of rebars even though they are designed as as Truss-Tie model. Not much reply on this thread, may be i am alone on this boat.

 

[hokie66]

Triangular primary reinforcement is the way I have always done it.

What do you mean by "headed dowels in the piles"? What is their purpose?

 

[BUGGAR]

Headed dowels have round heads attached to their ends to provide embedment strength without hooks. Remember when you have beam reinforcing intersecting from two directions over a pile with hooked dowels from the piles looking for a place to go? The headed dowels eliminate the need for hooks, which never point in the right direction anyway. I also use them at the ends of the main reinforcing to get away from hooks.

Headed bars are covered in ACI and have helped many an Engineer and Detailer to achieve sobriety.

 

[TLHS]

For three piles I'll usually throw a couple of bars in a triangle and then do skin reinforcement in whatever direction makes the bar cuts less stupid.

I'm pretty sure I've seen strut and tie done, though, when you have a grid or rebar that's not necessarily in the same direction as the load. It certainly conceptually seems like it should work.

 

[TXStructural]

CRSI Design Handbook uses bars across the piles (i.e., a triangle/3 ways), as direct tension ties (even though the design method is not strictly strut and tie. We are currently in the midst of a rewrite, including analytical work using strut and tie, sections (as in the current Handbook) and some new FEA. The research has found that the Handbook is conservative for all caps shown, but not excessively so. The new work also extends the caps to new jumbo pile sizes.