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krus1972 (Structural) (OP)
8 Aug 08 22:50
The edge distance from the edge of a pile to the edge of the pile cap is determined by the punching shear from the pile. I have a round augur cast pile that if it is placed on the exact edge of the pile cap on the two sides at the corner it will not create a problem with punching shear within the pile cap.   

The CRSI has minimum critera that defines the minimum edge distance from the edge of a pile to the edge of the pile cap. CRSI does not explain where and why this criteria was established.

Over the years I see that many designers place piles closer then the minimum edge distance as defined by CRSI.

My question is what is the REAL minimum edge distance requirement for piles and what defines the minimum edge distance if punching shear doesn't control?  Is it a constructablilty issue?

Any insite to this would be well appreciated.  

 
SlideRuleEra (Structural)
9 Aug 08 9:55
That's a good question, and I don't know the answer, but do have an opinion:

1. As you have suggested, constructibility. With a plus or minus 3" tolerance allowed by many specs on pile location, some "wiggle room" is needed to make sure the cap can be constructed exactly at the planned location even if the piling are off a little. And...

2. If the pile cap is underground, the protective rebar cover is, of course, 3 inches. To guarantee that the rebar mat completely covers the top of the pile, the edge of the pile cannot be any closer than 3" to the edge of concrete. I prefer to have the mat completely cover the the pile top to make absolutely certain that no (vertical) load can be applied to rebar "cover" concrete.

Add these two reasons together, and you get a minimum theoretical clearance of 6" between edge of pile cap and edge of pile.

Again, I don't know if any of this is true, but it seems a reasonable thing to do.

www.SlideRuleEra.net idea

www.VacuumTubeEra.net r2d2

civilperson (Structural)
11 Aug 08 18:06
CRSI says: "To prevent vertical edge splitting, minimum edge distance, E, to center of piles is 15 inches for pile capacity (P)< 60 tons, 21 inches for 60< (P) <120, 27 inches for 120 < (P) <200 and 30 inches for P > 200 tons."  
JKStruct (Structural)
11 Aug 08 21:59
agree with civilperson... I've used the CRSI edge distances as a minimum on my previous ACP designs.   
pelotoner (Structural)
12 Sep 08 8:38
I just delved into the strut and tie design for a shearwall pilecap.  However, a typical pilecap is very similar in design.  Most pilecaps are designed using the strut and tie method because of the efficiency of design and the increased accuraccy of the load path.

That being said, the bottom steel needs to be developed past the inside face of the pile.  This is where the critical tension section is located.  To obtain the appropriate embedment of the reinforcement, a hook is supplied at the end of the rebar and the additional embedment length (ldh, see ACI 12.5.2) is supplied.  Many times this dictates the minimum pile cover.

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