Base Plate and Anchor Bolts - Pedestal 2

[Eng-Tareq]

Hello All,

I have a question that I was wondering about for a while. Many steel column base plates are designed to sit on a pedestal that connects to any foundation type below. These pedestals are usually tight and slightly bigger than the base plate (maybe 2" in every direction). I was always wondering how these anchor bolts pass the code checks when it comes to "Concrete breakout resistance of Anchor in Tension" when the full length of embedment probably will not be realized as it can't develop in the concrete. Referring to Canadian codes (CSA A23.3-14 - D6.2) here:

h_ef=max(C_a,max/1.5; s/3)

Where:
h_ef: Depth of Embdement used in calculations
C_a,max: Maximum Distance from the Anchors to one of the closest edges
s: Maximum spacing between anchors

This h_ef value feeds directly into N_br: Basic concrete breakout strength of a single anchor in tension
Where:
N_br=k_c*Φ_c*λ_a*√f'_c*h_ef^1.5*R

So if you have a base plate slightly bigger than the column and a pedestal slightly bigger than the base plate h_ef becomes small, therefore how do these pass code requirements?

See a picture of a real-life example:

https://files.engineering.com/getfi...b774-4ee91a2d18b3&file=thumbnail_IMG_0742.jpg

 

[KootK]

Oftentimes engineers will bypass the breakout mechanism by justifying strut and tie informed offset laps between the anchor rods and the pedestal rebar. The, now classic, Widianto paper on the topic can be found here: Link

 

[WesternJeb]

I have been trying to get my firm to take advantage of Koot's reference for a while now. Thousands of engineers have taken advantage of the paper's advantages and I haven't heard of any failures that contradict this paper.

 

[KootK]

Thousands of engineers have taken advantage of the paper's advantages and I haven't heard of any failures that contradict this paper.

Meh, I wouldn't put much too much stock in that. Millions of engineers have done nothing at all for anchorage but to check tension on the rods and, somehow, that also has not caused many problems.

Interested parties would do well to follow the AISC research being done by this Kavinde fellow: Link. AISC seems to be throwing some real resources at improving this aspect of design. AISC seems to be throwing some resources at this issue, finally, and Kavinde's work seem to be pretty avant garde.