Shear Lug bearing capacity 3

[BAGW]

Hi,

AISC Design guide 1 provides different capacities for shear lug bearing against concrete (0.8fc) and column bearing against concrete (0.55fc). Why is there a difference? I know 0.8fc comes from ACI - 349. Is the difference because of different experimental setups?

Also, what value to use while checking shear lug bearing? I am tending to use 0.8fc as the design guide clearly states bearing capacity for shear lug as 0.8fc. Any opinions?

Thanks

 

[KootK]

Can you cite the pages for the two values?

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[BAGW]

Its on sheet 28 of Design Guide 1 AISC

 

[Celt83]

the paragraphs above the noted bearing equations note where those values come from.

Lug bearing is per D4.6.2 of ACI 349-06 phi*1.3F'cA1 phi = 0.65 so 0.85F'cA1 and column bearing is from 10.14.1 ACI 318-08 phi*0.85F'cA1 phi = 0.65 so 0.55F'cA1

Edit:
Didn't read your post fully you saw the ACI 349 reference. Difference may be confined bearing area below the surface vs surface bearing for the base plate. From commentary in ACI349 the 1.3F'c is recommended based on the tests described in Reference D.20 - Rotz, J.V., and Reifschneider, M., "Combined Axial and Shear Load Capacity of Embedments in Concrete," 10th International Conference, Structural Mechanics in Reactor Technology, Anaheim, CA, Aug. 1989.

So as you guessed seems to come down to the testing methodology.

Interestingly enough in their own design example 4.9 they use the column bearing formula for the lug design. Be sure to follow thru and check your shear failure for the concrete block in front of the lug as well.

 

[KootK]

Not sure it answers your specific questions but there's some good, related info here: Link

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[WARose]

[blue](BAGW)[/blue]

AISC Design guide 1 provides different capacities for shear lug bearing against concrete....

Don't mean to be getting (somewhat) off-topic, but I went to a seminar a few years back and the guy said those equations overestimated the capacity of that particular connection. (IIRC, I think he said by as much as 50% considering the side blowout capacity.) Not sure what has been done about it since but just wanted to point that out.