Steel Angle Ledger

[SteelPE]

Looking to do a project where we need to support new concrete plank onto an existing concrete wall with a steel angle ledger. I have two options in terms of angle position, option #1 toe up and option #2 toe down (see attached).

Both configurations offer some advantages over the other. However, I believe option #1 is better as you can rely on the plank to help reduce the tension load on the anchor. Basically the anchor will only see tension load from dead weight of the plank as once the dry pack/grout is in place the bending loads in the angle can be supported by the plank itself. Is reducing this tension load a valid option with option #1?

 

[TXStructural]

Using a WT section would get you the best of both. With a leg down, you can add stiffeners if needed for stiffness (removing the risk of bending of the horizontal leg.)

 

[BAretired]

Will there be a positive tie between the planks and the outstanding leg of the angle?

BA

 

[SteelPE]

I would be a bit worried about a WT as the "web" tends to be rather thin... but it is a good idea.

BA, the sketch is rough for the purposes of conveying the problem. In the end, I believe the plank will be welded to the ledger.

 

[BAretired]

The angle should be galvanized to prevent rust, so welding may be problematic. I believe it is important to tie the planks to the angle and if this can be accomplished, I would agree that the first detail is preferable.

 

[Stenbrook]

Me personally, I would go with option #2 and provide stiffeners for the leg if needed. I don't think I would consider the planks to help resist any tension on the top of the angle for option #1. But I also tend to stay a little conservative, especially on something like this.

 

[KootK]

I vote for option #1. With option #2, you get prying action on the bolts which can be quite difficult to predict.

It's a pity really, as I like the geometric simplicity of #2. I like that the angle fillet doesn't interfere with the precast and the welds to the plank embed plates seem cleaner.

However, I believe option #1 is better as you can rely on the plank to help reduce the tension load on the anchor. Basically the anchor will only see tension load from dead weight of the plank as once the dry pack/grout is in place the bending loads in the angle can be supported by the plank itself. Is reducing this tension load a valid option with option #1?

I don't believe this to be the case. In the final state, the plank and dry pack will rotate away from the wall and thus the dry pack will not really participate. With appropriate welds on the horizontal leg of the support angle you can, however, make an argument that you've moved the shear close to the vertical angle leg and thus eliminated most of the tension from the anchor. And this would apply to both options. I rarely do this though as it requires more attention to detail in the design and construction of both the embed plate and the connecting welds.



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.

 

[SteelPE]

This is a garage against an existing house, so it will need to be waterproofed and appropriately flashed. So I don't think the angle will need to be galvanized.

KootK

Missing from both options is a 2" concrete topping. The plank will be attached to foundation wall on 3 of the 4 sides of the structure (1 side being the existing concrete wall 2 sides being new). The 4th side is the entrance to the garage. So in this instance, for the plank to move, the entire structure would need to move and I don't think that is going to happen (that wasn't obvious in the thread above).

 

[Brad805]

Depending on the precast design gap your bolt heads might be in the way with option #1. Grooved welds will add to the cost and contractors tend to complain. Either option can be made to work and we have done it several times before.

 

[KootK]

@SteelPE: the new information doesn't alter my original recommendation. The planks, as simple spanning elements, will still rotate at the supports and separate slightly from the walls.

@Brad: are the groove welds that you mentioned the welds between the horizontal angle leg toe and the plank embed plates in option #1?


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.

 

[SteelPE]

Kootk,

In order for the plank to rotate about the support opposite the section the plank would need to move laterally away from the existing wall. Again, I don't think that is going to happen.

 

[Brad805]

Yes, I think you would might need to a groove weld in option #1. That will allow you to cut the bolt flush with the angle. The problem we find is you cannot prepare the angle before it goes to site, and doing so on site is more costly. Generally, we find 15 - 20% of the hilti bolts will need to move if they hit rebar or other constraints. We have found it is easier to cut a 2" or 3" square hole in the ledger angle and field weld a tab (with correct hole size) to the angle to make it easier to install. If you do not flush the bolt to the angle I suspect you will need a 1.5" design gap, and that I believe defeats the benefit. I suppose you could field grind the slabs for the bolts, but if that has to be done when it is hanging off the crane, the contractor would much rather you spec twice the number of hilti bolts rather than add that much crane time. I would go with option #2 and add a few extra bolts to add that comfort you need.

 

[KootK]

In order for the plank to rotate about the support opposite the section the plank would need to move laterally away from the existing wall. Again, I don't think that is going to happen

I don't see it. See sketch A below for the rotation that I'm thinking of that would be unaffected by lateral restraint. For sport, I threw in my favorite new construction version and an FBD of the angle model that eliminates/reduces bolt tension. I have to admit, however, that I'm finding Brad805's latest comments pretty persuasive.

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.