Facade Loads on Hollow Core Plank

[ROFSD]

Among the structural framing schemes being proposed for a 5 story Hotel is one that would have 8" deep hollow core plank spanning parallel to the exterior wall with a brick veneer finish supported by the edge of the plank. Plank spans would be at least 20 ft. Does anyone have pratical experience with this approach?

 

[spats]

You need a concrete beam at the parallel edge to support the brick. It is not practical to size the hollowcore for such an eccentric load. You may not need the beam at every floor if you can support two stories of brick at, say, the second & fourth levels.

 

[shin25]

Are you going to have a CIP topping on top of these hollow core precast slabs?

Your situation is almost like having bridge barrier on the sides of the deck.

Your design needs to account for proper distribution of load from the exterior wall to the adjacent slabs by shear and flexure interaction. A decent thickness CIP topping can handle this.

 

[spats]

Since I responded earlier, I have to respond to shin25... a brick veneer wall with metal stud backup, sheathing, etc., will weigh close to 50 psf. That's 500-600 lbs/ft on the edge of what's probably a 4' wide plank, for a 10'-12' story height. Normal topping is only 2", and it would not be sufficient to enhance the plank enough to carry such an eccentric load. You can't eccentrically (side-to-side) reinforce a prestressed plank.

Also, what about deflection? What about fighting the camber in the hollowcore at each level when the brick is installed?

I say an edge beam is the only real solution.

 

[shin25]

spats,

my comment was, "Your design needs to account for proper distribution of load from the exterior wall to the adjacent slabs by shear and flexure interaction. A decent thickness CIP topping can handle this."

If the above cannot be satisfied, then you are right, an edge beam may be needed. Or, the hollow core properly designed to carry this load.

 

[WpgKarl]

We have done this type of thing successfully in the past. The loads can be distributed into the adjacent slabs through the grouted shear keys between slabs. If there is a concern with load transfer between the shear keys, local pockets can be opened up between the slab joints and U-shaped shear friction bars can be grouted in place.

Supporting one storey of brick per level, on an 8-inch slab spanning 20 feet would work, based on what we have done in the past. We take the line load from the brick and magnify the shears and moments on the slab system as per the PCI Design Handbook - Load Distribution Method. This method empirically magnifies the shear stresses to account for the torsional stresses.

Note also that the brick wall load they give you would be conservative, as there will likely be windows - however, I wouldn't support more than one level of brick per floor.

As far as deflections go, we use the distributed load method to check the service stresses and deflections. We are wanting to do a mock up load test to see what the calc & actual deflections are as we are only approximating them.

The key is that the slabs are working together as a system to resist the loads. I would recommend proving solid concrete void fill in the edge void along with angles c/w anchors grouted into that edge void. However, you'll need to check if you need any more voids grouted.

 

[ROFSD]

Thanks to all for your helpful comments.

 

[JLNJ]

If the load is at the outside (exterior) edge of one plank it can't get re-destributed into the interior planks.

Call your precaster and ask him what they can handle. Then talk to the architect and mason about constructibility.

 

[cooperDBM]

The PCI load distribution method mentioned by WpgKarl includes a specific distribution for edge loading of an exterior hollow-core plank. This distribution magnifies the end shears to account for torsion and distributes some of the midpsan flexure to the adjacent interior plank, depending on the span length.

 

[jike]

An edge loading still has an effective width of slab that resists that load. The precaster usually has this info.

I would suggest that you check long term effects and how that may affect the deflections and joints.