Anchor Bolts with Embed W-Shape Welded to Anchors (Not Shear Lug)

[cpatt95]

Completing Seismic evaluation for project built in 1961 (near Charleston,SC). Anyone know the purpose of the wide flange welded to the anchors or have seen this before?
First thought was a shear lug, but it is not welded to the baseplate (all details are consistent and do not call out welds to the base plate)
Second thought was for breakout but why not place it at the bottom of the anchors?
Maybe to keep the anchors in place during construction (pouring of the concrete)? Idk any help would be appreciated.

 

[dik]

No idea... first time I've seen this. I generally stipulate that anchorrods are installed using a template, and it's not often that there is a problem.

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Do you feel any better?

-Dik

 

[GC_Hopi]

Someone previously posted a similar design and it was an shear lug. Link I think it is an uncommon shear lug method that has fell to the wayside.

 

[KootK]

Like GC_Hopi, my money's on a misguided attempt at a shear lug. It's hard to believe now but, back in the day, the thinking on anchorage used to be quite different:

1) Much less testing was available.

2) Much less literature was available.

3) The internet wasn't around to help disseminate what was available and to connect technically weaker engineers with technically stronger ones.

Still, to this very day:

4) It is common to use hairpins at PEMB anchorages which has a similar problem with bolt bending and;

5) Never does a 12 month period pass where I don't encounter at least one base plate design where the shear anchorage "check" is nothing more than having checked 0.6Fy shear on the bolts.

When you think about it, few things could probably be worse for shear breakout than to have such a big discontinuity in the concrete right in the middle of your pier.

 

[JStephen]

In the olden days, anchor bolts were assumed to develop the load through friction at the bolt-concrete interface. Following that reasoning, that detail would furnish a whole lot more friction-area.

 

[GC_Hopi]

KootK: Can you elaborate on what you mean in #4? You are not a fan of hairpin reinforcement like this.. just curious/maybe there is an alternative scheme

 

[MotorCity]

Maybe to increase the surface bond area to resist pullout/uplift?

 

[KootK]

You are not a fan of hairpin reinforcement like this.. just curious/maybe there is an alternative scheme

I'm fine with the particular sketches that you posted as those are:

1) Embed plates small in scale.

2) ACI approved.

3) Backed by testing.

4) In my opinion, the rebar is primarily fastening the breakout frustum concrete to the surrounding concrete. The requirement to run the bars behind the anchors is just feel good bullshit in my estimation. Anchors bearing on rebar isn't really a viable load path.

It's the condition shown below that I don't like. Much heavier loads and, I believe, an intent to transmit shear directly from the anchor bolts to the hairpins. Some more reliable alternates include:

4) Direct tension ties detailed properly.

5) Resist the overturning at the pier foundation.

I still do the hairpins myself sometimes but I don't feel especially good about it.

 

[KootK]

@cpatt95: what's the situation where this detail is applied? Braced frame? Moment frame? Neither? I can now see this being either a shear lug or an attempt at improved uplift resistance. Knowing the situation might tilt things in one direction or the other. Not that it's a great detail either way.

 

[cpatt95]

@KootK: it is apart of a braced frame with braces in both directions. But I don't see it really helping with breakout due to tension with the anchors being 2' and the wide flange section being only 6" long and being 1" from the top of slab.

 

[cpatt95]

See following screenshot without my edits. You can see the breakline in the anchor bolts.

 

[KootK]

Is this a two bolt connection or a four bolt?

Am I seeing a 3/8" base plate?

 

[cpatt95]

Yes it is a two bolt connection....

And kind of....it's two 3/8" plates stacked on top of each other.