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# Re: Anchor Bolts embedded in Reinforced Concrete

• To: seaint(--nospam--at)seaint.org
• Subject: Re: Anchor Bolts embedded in Reinforced Concrete
• Date: Fri, 30 Jul 2004 12:15:16 -0700 (PDT)

PCA was the first to come out with a publication for anchor design. Its formulae were restricted to unreinforced concrete, though it was not mentioned so anywhere in the booklet. I expected ACI 318, Appendix D to do much better than PCA. My hopes were in vain. ACI 318 App D was practically a copy of PCA. Somewhere in that document there was a passing mention of a need to design reinforcement if the capacity requirements, according to the listed equations, were not met. There were no suggestion for designing the reinforcement to transfer the anchor bolt forces to the concrete. Most concrete foundations in practice do not have the width and length required to deliver required capacities derived from unreinforced considerations. Thus the equations in ACI 318 have very limited practical use. The adaption of the equations and their extrapolation to real life foundations has been left to the judgment of the engineers.

For taking care of anchor bolt tension, I use the development length concept to determine bolt embedment. For lateral force transfer, I don't have a uniform methodology.

Rajendran

"Kestner, James W." <jkestner(--nospam--at)somervilleinc.com> wrote:
I have recently waded thru all the formulae in ACI 318-2002 Appendix D for computing anchor bolt capacities! IBC 2000 Section 1913 is similar. Wow!

It seems all the formulae are based upon capacities of unreinforced concrete.

When anchor bolts, subjected to shear, are embedded in a reinforced concrete pier, it would seem that the ties will work like stirrups to resist the shear if they are spaced at d/2. For some pier sizes, the d/2 requirement is a tighter tie spacing than normally required for piers. The compressive force in the pier (if there is any) will obviously increase the shear capacity. To prove that the anchor bolts are OK in shear, it seems logical to check the allowable shear of the reinforced pier instead of the breakout strength of the anchors in the unreinforced concrete. Steel strength and pryout strength of the anchors also need to be checked.

When anchor bolts, subjected to tension, are embedded in a reinforced concrete pier, it would seem that the overlap of the anchor bolts and the reinforcing steel has to be long enough to transfer the tensile forces. To prove that the anchor bolts are OK in tension, it seems logical to check the tension that can be transfered to the reinforcing instead of the breakout strength of the anchors in the unreinforced concrete. Of course, the steel strength of the anchors also need to be checked.

I would then use the minimum values of the capcities in the combined stress equations.

For anchors in footings, I use the formulae in the code for anchors in unreinforced concrete.

Is this how others are currently doing it or are you relying on old tables like I used to? You need a major spreadsheet to handle these new calculations. Pretty involved process!

> Jim K.

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