Steel Bar Joist Supported on Steel Ledger 1

[omoreno80]

I have an LH series steel bar joist spaning about 40' spaced at 4" o.c. The architect is sugguesting to to support the bar joist via a steel ledger attached to the side of masonry wall. While it would facilite the construction of the wall, I am concerned about the viability of this connection. This connection will add a Pe/2 moment to my wall. I can handle this with additional reinforcement, but I am concerned about the connection itself. I typically like to see the bar resting on top of the wall. Now, besides the combined bending and torsional moments imposed on the ledger and the problems with anchoring this connection on the wall. How can I accomplish any shear transfer to the masonry walls below? I believe the bar joist has some rollever capacity, but I am concerned on how to transfer the forces from the steel deck to the masonry. I have not heard got things about this connection from a collegue. Any ideas anyone. Thanks

 

[JAE]

You are correct to be concerned about the eccentric moment induced on the wall from the joist. The distance from the center of wall to the joist bearing might be as much as 6 inches (wall thickness/2 + 1/2" wall to joist clearance + 2" to joist bearing).

The problem with putting a moment at the top of a wall is how to develop the bending reinforcing above the joist bearing. A vertical bar in the wall (with no parapet) must terminate near the top of the wall and this might not be enough distance.

Secondly, the ability to anchor a steel angle to the wall and support 40 feet of joist is questionable in light of the fact that you also have lateral shear to take through the same bolts that support the gravity loads.

To get the shear down from the deck diaphragm and into your support angle you need to have a second agnle along the top of the joist to serve as a diaphragm edge collector. You can then transfer this shear down to the support angle by including short segments of 5" deep channels or tubes between the joists.

 

[omoreno80]

Thank JAE for the response. I also had the thought of having an additional continous angle directly underneath the deck anchored to the side of masonry wall. In other words, a larger steel ledger to support the bar joist for gravity and uplift loads (lets say 6x6-LH series requires 6" bearing so this may have to be larger) and a smaller one at the deck level (lets say 3x3) to transfer the diaphragm shear loads to the masonry wall. So the deck and the bar joist would be in between two sets of angles. Has anyone dealt with this type of connection? It seems to have some applications in residential masonry construction as I have researched this out. But I cannot find a commerical building application on this.

 

[BAretired]

If the joists are spaced at 4'-0" o.c. (not 4") you do not have to tie the deck to the wall. The deck is tied to the joists and the joists are anchored into the wall.

A continuous ledger is possible, but it adds moment to the wall for no good reason. Much better to anchor the joist shoes directly to the masonry using standard details.

BA

 

[JAE]

BAretired,

Typically joist manufacturers do not like engineers to depend on the joist seat taking lateral load (perpendicular to the joist).

I've seen some engineers demand on their plans that the joist mfr. provide X kips rollover capacity, but SJI doesn't seem to be too keen on this idea. Thus, a continuous deck edge angle (on top of the joist, under the deck) is used to tie the deck pieces together and collect the load into one long steel piece. The lateral force in this collector then needs to be delivered to the wall in one of three ways.

1. Anchor the angle directly to the wall.
2. Add tubes/channels between the deck angle and the supporting steel below the joist (which is anchored to the wall).
3. Demand that the joist seats have rollover capacity and thus the lateral shear is taken through the deck angle, into the joist seat, and then into the steel support, which is connected to the wall.

All three of these work, except that number 3 isn't acknowledged by SJI that I'm aware of.

 

[BAretired]

JAE,

On further thought, I agree that a more positive tie is needed between deck and wall. Thanks for pointing that out.



BA

 

[omoreno80]

The joist roll-over capicty might be an idea, my shear loads are pretty low. It may over stress the anchor bolt connecting the angle to the wall. I'll examine that option. The continous angle would provide my sidelap fastening at the deck. Thanks for the idea JAE.