Column Pedestals - Do Stirrups Need to be Developed?

[sticksandtriangles]

We've got a debate in the office if stirrups used to resist a concrete breakout failure plane in typical shear lug need to be developed on both sides of the failure plane in order to be effective.

Do the stirrups that do not meet Ldh on the free edge of the failure plane fail to develop Fy?

A counter argument to this is that for small depth beams, the same shear equation is utilized, regardless of development length.

Does anyone have a code reference/testing that makes a statement regarding the need for development of this reinforcement?

One item found this statement in the best paper on anchoring to concrete,

https://www.sefindia.org/forum/file...forcement_a_petrolium_project_papers_199.pdf,

it looks like they recommend 20ksi max on the 135 end seismic hook. No mention of Ldh.

Thanks!

S&T -

http://www.re-tug.com

 

[BridgeSmith]

So, right at the one corner, the stirrup/tie is only partially developed. If you're designing close enough to the capacity for it to matter, I'd say just add an extra tie. You'll spend more time trying analyze it than it's worth to save a couple pounds of steel.

Rod Smith, P.E., The artist formerly known as HotRod10

 

[Celt83]

edit: same paper you already found.

Leans on curved bar node theory in strut and tie models to pass the tension around the stirrup bend. I believe they indicate a reduction at the the 135 degree tails.

 

[KootK]

There's a provision for beam stirrup anchorage that allows you to consider a hooked bar developed almost instantaneously so long as:

1) There's a longitudinal bar inside the stirrup bend and;

2) The stirrups are #5 or smaller.

I've been employing that same relaxation to situations like this.

 

[bugbus]

Agree with KootK

 

[bones206]

I follow the hooked anchor approach that the paper proposes. Here is one implementation in a design spreadsheet:

http://asp.civilbay.com/15-anchor-bolt-all/02-shear-key/01-aci349-06/calc.aspx

 

[sticksandtriangles]

Thanks everyone, as with most things, it doesn't look like there is a definitive answer on this.

I have generally followed KootK's approach, if it is in the shear failure plane and anchored by a longitudinal bar, assume it is fully developed and move on with my design. Looks like maybe that reference is 25.7.1.3 in ACI 318-14 that Koot mentionded.



S&T -

http://www.re-tug.com