what is the bearing area formula for anchor bolt plate?

[delagina]

I'm looking at aci/pca and it has a chart for bearing area of anchor bolt head.

what is the bearing area formula for anchor bolt PLATE?

 

[ingdaniel]

The area of the plate less area of the bolt.

 

[delagina]

it's been sometime since I've done this manually so bear with me.

my understanding is even if I add plate at the bottom of anchor bolt,

I'm only increasing pullout strength.

I'm still not increasing concrete breakout strength?

any other option of increasing concrete breakout strength?
Anchor bolt is embedded on a footing, no pedestal.
I initially want to add hairpin/tension reinforcement but anchor bolt embedment is already the same depth of footing.

 

[delagina]

in summary,

what are the option to increase concrete breakout strength of anchor bolt in shallow slab?

 

[JStephen]

Depending on how shallow, you may can still add shear reinforcing in the footing.
Options: Adjust slab dimensions, increase concrete strength, reconfigure anchor layout.
Double-check the psi factors, see if any of them can be increased.

 

[delagina]

I don't understand how shear reinforcing would help, my main concern is tension on anchor bolts.

slab thickness and anchor bolt distances can't be change. anchor bolt distance is dependent on base plate holes which cant be change.

 

[delagina]

after some googling I saw this..
this is similar to hairpin tension reinforcement but since slab is too shallow they anchor it to longitudinal bars..
any comments..

Since ACI 318-08 explicitly allows using reinforcement developed on 4 sides of the concrete breakout frustum as the design strength instead of determining the concrete breakout strength per Appendix D, we use stirrups, anchored to 4 additional longitudinal bars in both directions of the ATS rods to absorb the heavy uplift.

 

[jvvse]

Sorry to show up late. There is a lot of interpretation with what is applicable when using bearing plates.

ACI 318-11 is a little more explicit with what is applicable. D.2.2 specifically says that multiple anchors connected to a single steel plate are not applicable, and D.2.3 does not mention a single anchor connected to a bearing plate. It's obvious that putting a 3" square bearing plate at the end will have more resistance to pullout/breakout than a simple headed bolt.

At least, you can take Abrg from the edge of the plate instead of from the center of the bolt without any argument. At most you can probably check the bearing plate for punching shear instead of Appendix D. We do the latter for plates connected to multiple anchors.