Pin Connection - Slotted Hole

[Jerehmy]

I have a situation where I need to be certain that a beam has a pinned and not a moment connection. It's a clip angle with a two bolt connection to a beam and 2 adhesive anchors to a concrete wall. The adhesive anchors can't take the full moment.

I wish to horizontally slot the top bolt hole to ensure a pinned connection. Has anyone done this with good/bad results?

Thanks

 

[thaidavid40]

A short slot on the bottom, and a long slot on the top, sure seems like a reasonable proposition to me. I should think in this case that the connection bolts should be only finger-tight, just to preclude any clamping friction from transferring additional strong-axis moments.
Dave

Thaidavid

 

[Jerehmy]

What's the purpose of the short slot in the bottom hole?

 

[KootK]

Unless loads are very light and things will remain very clean (corrosion etc), slotted holes tend to make pretty unreliable movement joints. The bolts tend to plow a bit perpendicular to the slots and lock up.

When I've had the same concern, I've bolted a plate to the concrete and then used clip angles with three sides welds to connect the beam to that plate.

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.

 

[Jerehmy]

Loads are light (1.6 kip shear, ASD) and its aluminum members with stainless steel fasteners. It's in a wastewater treatment plant. The location of this particular beam is above a non-potable water pit, not sewage.


That's a good idea too. I may have to see which one the fabricator prefers because they get all whiny when it's not a typical detail they use.

 

[bowlingdanish]

Why is it a concern that the adhesive anchors can't take the full moment? Surely the connection would permit some rotation before it failed.

 

[Jerehmy]

The point is, how much? I did an experiment in grad school where we tested several connections. Pinned connections weren't entirely pinned, somewhere in between. Same for moment.

Also, the pinned connection with the angle welded to the supporting member and bolted to the supported member is fairly flexible because of the small return at the top of the angle. I'm not sure how flexible an angle with two adhesive anchors is compared to the welded angle.

It can take maybe half the moment. If something simple like a slotted hole can alleviate most of the moment, I'd like to do it.

 

[CANPRO]

If you wanted to get real technical on the slots, wouldn't they have to be sightly inclined to match the expected rotation of the beam? Otherwise the top bolt will pull down on the top slot and the bottom bolt would push up on the bottom slot. I'm sure this isn't an issue, just thought I'd throw that out there.

Can you adjust your anchor detail to give yourself some more wiggle room with the potential moment?

 

[Jerehmy]

hmm.

First, the angle of rotation is very small so the bolts shouldn't really come do what youre saying very much.

Second, the forces are all vertical so per the code the slots must be perpendicular to the force, which they wouldn't be if I inclined the slots.

No, the reason they don't work is because the concrete edge distance is only 3-5/8" for the top anchor. Pullout is an issue. And they're post installed plus we are just a sub so I can't reinforce the anchors. Another option is seated angle support but then I'd need brackets near the top to prevent rotation which is a pain.

 

[Jerehmy]

I could actually just bolt to the seated angle to prevent rotation since the loads arent very high and the member isnt very deep.

 

[thaidavid40]

@Jerehmy,
The short slot on the bottom is to allow for usual fit-up tolerances - just like any normally fit steel-to-steel connection. The long slot allows for that, plus the hoped-for rotation.
Dave

Thaidavid

 

[CANPRO]

I wasn't suggesting to actually incline the slots. I guess what I was getting at is I don't think the horizontal slots will provide any additional rotation in the beam.

It's late and I've had a long day so maybe I'm not following, but why do you need brackets to prevent rotation? I thought you were trying to achieve a near true pinned connection?

 

[Jerehmy]

maybe twist would have been a better word for me to use as I meant rotation perpendicular to the length of the beam. long day here too, nothing a cold oktoberfest wont fix! (recommend spaten's).

 

[CANPRO]

Ah, I see what you're saying.

Cold beer helps with the long day...not sure reading eng-tips late at night helps much, although it's interesting following a few eng-tips heavyweights debate long-term concrete deflections!

 

[RPMG]

A few thoughts:

1. Bolting near the neutral axis should reduce translation at the bolts

2. Excluding thread's at the shear plane improves ease of rotation

3. Welding aluminum reduces its strength significantly

4. I would think that 2 short slotted holes would be better than 1 standard and 1 long

5. Old connections with rivets had bolts staggered at the clip angle to reduce eccentricity. The beam side bolts should be higher than the support side. I believe that bolt offsets were 1 3/4" vs 2 1/2"

6. Is there space to use an L8 with 4 small adhesive anchors?

7. The seated connection sounds like a good alternative because it's symmetric, but wouldn't the top stability piece create the same problems with moment.

 

[Jerehmy]

Too stability piece wiuldnt be connected. itd be like a clip on eitber side that isnt bolted so it can rotate for moment but cant twist

 

[RPMG]

Were you planning on using 1 horizontal row of fasteners?