Anchor Bolt - Masonry Crushing 1

[StrEng007]

Does anyone know how Equation 8-7 used in TMS 402-16 is derived?

This mode of failure uses the area of the anchor bolt for crushing of the masonry. I thought crushing in this scenario would be dependent on the depth of embedment.

I'm seeking this out because I'd like to determine the shear capacity of an anchor through the face shell of hollow CMU (actually, through bolted to the opposite face of wall). It's in the field of the wall (not close to any wall edges). I figured that pryout and breakout wont be applicable. Wanted to consider the crushing area as a function of the anchor's diameter and the thickness of the face shell.

 

[SwinnyGG]

Are you doing this just for fun?

What you're after is in the Hilti book. I don't see any reason you'd want to calculate it yourself.

 

[StrEng007]

Hilti does through bolts into hollow masonry walls with bearing plates at the opposite face? I didn't realize that.

 

[jerseyshore]

TEK 12-3C is very useful for these calcs:

https://ncma.org/resource/design-of-anchor-bolts-embedded-in-concrete-masonry/

 

[JStephen]

A similar situation in concrete, see ACI-318-14, commentary on 17.4.3.4.

 

[dik]

I generally like to know...

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[dik]

Thanks, jersey...

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[phamENG]

No, Hilti does not cover this situation. If you do some searching, you'll find that no technical publication does a great job of covering this scenario. I think there might be some literature as it relates to non-participating infill connections for steel frames, but that's about it and is very narrowly tailored to that use case.

It is odd that there's not more out there on the derivation of that equation. You may want to reach out to The Masonry Society or NCMA and see what they have to say. (The Tek jersey posted is good, but doesn't get into the derivations - it's a how to, not a why do).

With a through bolt you have to draw out a FBD of the whole thing, and look at the bolt as a simple beam with a point load on the overhang. Then compare your reactions to the various shear capacities. Make sure they epoxy it in or you won't have good bearing at the face shells.

 

[dik]

...and once the concrete crushes locally it takes more load.

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[StrEng007]

Thanks all.

Yeah, I've been through the publications from NCMA and BIA and there doesn't seem to be any derivations. I like the ACI section JStephen pointed out. There is most likely a similar explanation where the equation was derived based on local crushing of the masonry as some logical embedment or thickness of the masonry unit.

Pham, thanks for mentioning the epoxy. Such a simple thing but really provides a lot of QC.

Based on my FBD, I have to consider the combined effect of bending, shear, and tension. I've been around in circles trying to evaluate these combined forces for typical baseplates (that's a whole other topic). I've reread Design Guide 1 and there doesn't really seem to be a consensus on how to actually combined these forces, but rather how to avoid the calculation by making assumptions, providing grout, shear lugs, applying 0.8 factors, 2 bolts in shear etc. The only mention I've seen about combining these forces has to to with the fatigue equations.

 

[jerseyshore]

I've talked to TMS/NCMA people before and they are very helpful, worth a shot.