Pile cap edge

[Enhineyero]

Hi all. I was wondering why most of the pile cap design adopt a pile face to edge of pile cap distance of 150mm? i assume that if concrete cover is 75mm (3") and ties diameter is 16mm (5/8") and rebar diameter of 32mm (5/4") = 123mm or 125mm (5") that is a conservative estimate of the pile face to edge of pile cap distance. because we can still reduce 75mm concrete cover by use of formworks, and using a smaller rebar diameter.

but why adopt 150mm?

 

[slickdeals]

One of the important things is that pile caps work as a tied-arch. Once you do a Strut and Tie analysis, the requirement is that the reinforcing bars (tension tie) be developed on either side of the "node". In this case, the more distance you have toward the edge helps you to develop the hooked bar.

Also, in thinner pile caps, you should be checking corner pile's punching shear capacity, although it rarely controls for normal pile caps.

One other thing is that the piles are more than frequently allowed to be installed with lower tolerance levels. I remember 3" being an acceptable number.

 

[wannabeSE]

The IBC specifies a 4" minimum. Larger dimensions help with punching shear. Also, the larger distance may be intended to accomodate the construction tolerances of the pile location.

 

[asixth]

The concrete code which I use (Australian) specifies that at least 50% of the reinforcement be developed at the start of the nodal zone (pile edge) and that the development of the reinforcement at the node (pile centreline) be used for the design when strut-tie design is used. This 150mm allows for cover, a cog or hook to be placed (I think the internal radius is 5*db for cogs) and allows for a good portion of reinforcement development but the time you get to the pile centreline.

It also allows some tolerance, driven piles will have a 2-3" driving tolerance and unless the installed pile is outside this tolerance, the reinforcement scheduler will not allow for minor dimension changes following pile installation.

 

[Enhineyero]

Thank you for all your replies, now i know that its mostly for site considerations