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Re: FW: Anchor bolt with plate at bottom

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Ravi,

If you have not discovered this yet, the analysis and failure mechanism for headed bolts and rebar is much different.  For headed bolts it is assumed that there is no bond along the shaft and the head is sized just large enough to initiate a shear cone.  Tests have shown that a standard heavy hex head or nut meets this requirement.  As for using plates, you would think that larger is better but in fact larger plates can significantly effect your anchor bolt design once you start running the numbers.  For rebar it is assumed you have continuous bond along the entire length of embedment.  As far as using the two together, you assume your anchor bolt will develop the shear failure cone then at some point the cone will intersect and transfer the load to the rebar.  ACI has been terrible in providing supplemental rebar guidance and details however ACI 318-08 has finally provided a limit set.  The two requirements you need to be aware of are is that the rebar must be within 0.5hef of the anchor bolt and that the rebar needs to be fully developed on each side of the intersection point (i.e. straight length development or hooks).  See ACI 318-08 for all the other detailed requirements.

Thomas Hunt, S.E.
Fluor



"Vasu, Ravi" <Ravi.Vasu(--nospam--at)jacobs.com>
08/06/2010 07:06 AM
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FW: Anchor bolt with plate at bottom





List,

I need to know the difference between headed anchor bolt(A36, A307….) and anchor bolt with plate at bottom.  
I have a case of Steel column sitting on a concrete pedestal with rebars.  (ductile design
in SDC D)

1.  We need to develop the anchor bolt by providing sufficient rebars.  The (headed)anchor bolt length depends on the development length

of rebar we provide.  'ASCE guidelines on anchor bolt' gives steps to do this.

2.  Is providing a anchor plate, say 5 in dia for 2 in anchor bolt(at bottom) can reduce the Anchor bolt length by lot?  if we follow the 45 deg.

failure plane from the edge of the plate to the rebar, It does not reduce the bolt length by more than plate width/2.  That is hardly 2 to 3 inches

difference compared to headed bolt case in this case.  If so, what is the use of providing the plate?  Am I missing something here?

In certain cases, concrete compaction below the plate may not be good.

Appendix D, ACI 318, section D5.2.9 & D6.2.9 refers to take rebar strength instead of concrete breakout strength
In determining rebar/length in accordance with Ch. 12 (or Ch. 22 for seismic).  It does not say any detail about
anchor bolt w/ plate.  In the definition for anchor it says about hooked or headed bolts only.

Is there any reference material available?

Pl. let me know.  Thanks

Ravi Vasu

 
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