Headed Anchor Rod Confinement Steel per ACI

[scanf1027]

I am trying to understand the provisions of ACI Appendix D (318-08), specifically Section D.6.2.9 on anchor confinement reinforcing. To me, the code doesn't specifically state how to design the confinement steel, but states the steel must be developed in accordance with Chpt 12.

I checked in the PCI Design Handbook and it uses shear friction. Why shear friction? Is the thinking that the confinement steel isn't engaged unless the concrete cracks considerably, so you want the shear friction to equal the shear force?

Any suggestions or comments?

 

[JennyNakamura]

Google "Design of Anchor Reinforcement in Concrete Pedestals" by Widianto. It will describe in detail how to do what you are trying to do. It's a paper by some guys at Bechtel. As you say, the code doesn't give much guidance on supplementary reinforcing; this paper will be a big help.

 

[amec2004]

What you are taking about is the Anchor Reinforcement which is newly codified in ACI 318-08. Clause D.5.2.9 is on anchor reinforcement for tensile resistance to replace concrete tensile breakout strength, and clause D.6.2.9 is on anchor reinforcement for shear resistance to replace concrete shear breakout strength.

ACI 318-08 and other ACI publications, PCA notes on ACI 318-08, ACI 349.2R-07 Guide to the Concrete Capacity Design (CCD) Method-Embedment Design Examples, ACI 355.3R-11 Guide for Design of Anchorage to Concrete: Examples Using ACI 318 Appendix D, didn't give the specific example on how to calculate Anchor Reinforcement for shear as per clause D.6.2.9

One of the popular reference for shear Anchor Reinforcement calculation is from Bechtel technical publication

Design of Anchor Reinforcement in Concrete Pedestals by Widianto, Chandu Patel, and Jerry Owen

It's available for download at

http://www.bechtel.com/assets/files/TechPapers/design-of-anchor-reinforcement.pdf

The anchor bolt design spreadsheet created based on above reference, not from the original author, is available for download at

http://www.civilbay.com

The anchor bolt design spreadsheet provides both options: using anchor reinforcement and without using anchor reinforcement, for group anchor capacity design.

 

[Lion06]

ACI 318-08 is pretty clear on how to design reinforcement to take shear and tension breakout off the table. It wasn't clear in '05, but it's spelled out very clearly in '08.

 

[amec2004]

I think ACI 318-08 is clear on the requirement of development length ldh beyond failure plane, or anchor reinforcement to be min(0.5ca1, 0.3ca2) away from anchor rod etc, but not clear on how the shear force get transferred from anchor rod to horizontal anchor reinforcement. If I miss anything, please provide more details on the ACI 318-08 provision on shear anchor reinforcement calculation.

Anchor Reinforcement is not mentioned in ACI 318-05 code.

I cannot find more details on shear anchor reinforcement calculation in the ACI 318-11 code either, hopefully ACI can give more insights in the future publications? or we can find some formal procedure in the coming 2012 Edition of ASCE Design of Anchorage in Petrochemical Facilities ?

 

[scanf1027]

Lion06,
Where in D.6.2.9 does ACI explain how to design the anchor reinforcement?

Thanks for your responses.

 

[Lion06]

It's telling you that you an use the reinforcement instead of the concrete breakout strength. The reinforcement is in tension, so it's pretty clear that you design the reinforcement as As = Vu/(phiFy), where phi is 0.75.

The shear force gets into the reinforcement by virtue of being hooked around the anchor - i.e. fully developed on both sides of the plane.