Bored Piers/Piles Central Tensile Bar 1

[MHassanAbdi]

We are building a raft with bored piers/piles. The site team have cut the tensile central bar flash with the concrete pile cut off level , while they left Pile cage reo projection as per the required projection(1000mm into the Raft ). The issue I have is does the tensile central bar need to go all the way into the raft ( 1500mm Raft) ?. Currently the Central bar is only intruding 50mm into the 1500mm Raft. What do you guys think ?

 

[HTURKAK]

What is central reinf. ? A sketch would help to see your problem. If the raft found. transfer bending moments and uplift, you need to extend the rebar cage. Check your case if the piles subject to bending and uplift. If necessary , you may use welded lap reinf.

The following figure from TOMLINSON, Pile design and construction.

He is like a man building a house, who dug deep and laid the foundation on the rock. And when the flood arose, the stream beat vehemently against that house, and could not shake it, for it was founded on the rock..

Luke 6:48

 

[BAretired]

Reinforcing steel should be adequate to resist loads, including bending moment. If some bars have been cut off too short, they must be spliced in accordance with code to develop the full strength of the bars. A bar terminating at the pile cutoff doesn't do much good for the connection from pile to pile cap.

 

[SlideRuleEra]

...the Central bar is only intruding 50mm into the 1500mm Raft.

The central (tension) bar is probably much larger in diameter than bars in the cage. Chip down into the the bored pier's concrete. Depending on bar size, expose (and clean) another 25mm+, of the central bar (making the total exposed length of the central bar 75mm+. Use a CADWELD Rebar Splice, with end packing cap to make the (same size) spiced rebar as long as required... and develop full tensile strength.

This type splice is routinely use for electric generating station foundations.

 

[BAretired]

My thanks to SRA for the explanation. I have not encountered the use of a central rebar, but the Rebar Splice appears to be the logical answer.

 

[Just Some Nerd]

I've had a scenario at my company where the larger inner bar is there primarily for the lower portion of the piles where the moments/shears were lower (~20m deep overall with the top 8m having the cage) while the cage was doing all the work for the upper portions.

The engineer who designed this would know the specifics of what reinforcement the pile needs where, so ask him whether what you've done is a problem or not.

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Why yes, I do in fact have no idea what I'm talking about

 

[WestLevel]

Just for my knowledge. When they design these with the larger tensile bar in the center. Is it basically a simpler way to design a pile/piletop where there is moment and tension? So you just plunk a large bar in the center for tension and then the cage for the moment?

 

[SlideRuleEra]

WestLevel - Your description is exactly right. We used proprietary DeWaal piling for one of our generating stations. Installation was quick; the piles have performed as expected.

I have no interest in or connection to DeWaal piling or the contractor that installs them.