Minimum embedment of a steel pipe into a concrete cap?

[abusementpark]

The CRSI Design Handbook indicates a minimum 6 inch embedment for steel piles into concrete caps, stating that it is a good practice for structural steel shapes to avoid use of cover plates for bearing.

Why would embedment affect the bearing capacity at the interface between the top of the pile and the cap? It seems to me like it would all be based on contact area. Why would the embedment matter? I know a certain amount is required for lateral stability.

 

[dik]

I don't know where the numbers come from, but the embedment would help increase bearing by confinement.

Dik

 

[Ron]

Friction interface between the steel and the concrete adds to the bearing...the more embedment, the more capacity.

 

[abusementpark]

I don't know where the numbers come from, but the embedment would help increase bearing by confinement.

Is the embedment contribution quantified somewhere? What if I can prove that the top of the pile meets ACI's bearing provisions?

Friction interface between the steel and the concrete adds to the bearing...the more embedment, the more capacity.

I thought natural friction bond between concrete and steel was minimal without an applied normal force. How would you calculate the contribution from the friction interface?

 

[Quanski]

I highly doubt the friction between the non-deformed steel surface and the concrete is of any significance. What type of pile do you have? pile or H?

 

[abusementpark]

Circular pipe pile.

 

[LOKSTR]

See the link for effect of pile embedment for different conditions under lateral load.

 

[BAretired]

That link didn't work for me.

I would not rely on friction between steel and concrete. I can't see anything wrong with using a cap plate if you need more bearing area.

BA

 

[LOKSTR]

Try the link by copy and paste in a new window.

ntl.bts.gov/lib/35000/35400/35444/UT-10.16.pdf

 

[charliealphabravo]

The 6-inch embedment looks like a prescriptive minimum for stability and integrity of the connection under vertical and lateral loads. It is basically just twice the cover requirement for reinforcement in concrete cast against earth. I can't imagine that it is an actual calculated criteria since breakout strengths of the cap would depend on the reinforcement size and configuration.