Ponding of Concrete on Composite Steel Deck Floor
Ponding of Concrete on Composite Steel Deck Floor
(OP)
When I've used composite floor decking over steel beams in the past, I've typically cambered the joists to avoid ponding issues with the concrete topping.
On my latest project, we're going to go with unshored, uncambered steel beams beneath the composite deck. Therefore, the concrete will pond to some degree.
How have others gone about accounting for the additional dead load due to concrete ponding in this situation? I've read a couple of articles on the subject and it sounds quite daunting.
The steel decking deflects and increases ponding; the steel infill beams deflect and increase ponding; the supporting girders deflect and increase ponding... on and on it goes. And it's iterative to boot.
Is there a simpler yet still rational way to deal with this?
Also, where the ponding occurs, flexural capacity will also increase as result of the increased effective depth of the system. Is this typically utilized?
Thanks for your help.
KootK
On my latest project, we're going to go with unshored, uncambered steel beams beneath the composite deck. Therefore, the concrete will pond to some degree.
How have others gone about accounting for the additional dead load due to concrete ponding in this situation? I've read a couple of articles on the subject and it sounds quite daunting.
The steel decking deflects and increases ponding; the steel infill beams deflect and increase ponding; the supporting girders deflect and increase ponding... on and on it goes. And it's iterative to boot.
Is there a simpler yet still rational way to deal with this?
Also, where the ponding occurs, flexural capacity will also increase as result of the increased effective depth of the system. Is this typically utilized?
Thanks for your help.
KootK






RE: Ponding of Concrete on Composite Steel Deck Floor
You also have to remember that each beam will have a natural camber and that the fabricator is suppose to place the camber in the upwards direction, so even if you don't specify camber you will always end up with at least a little.
RE: Ponding of Concrete on Composite Steel Deck Floor
RE: Ponding of Concrete on Composite Steel Deck Floor
RE: Ponding of Concrete on Composite Steel Deck Floor
RE: Ponding of Concrete on Composite Steel Deck Floor
Don't count on any increase in capacity due to increased section.
WillisV's approach is good. You might want to increase the percentage to 15 if your design is stretched.
Another consideration...place the concrete in two lifts. You can put stud rails in the bottom of the flutes to tie together the two lifts.
RE: Ponding of Concrete on Composite Steel Deck Floor
RE: Ponding of Concrete on Composite Steel Deck Floor
Their recommendations include limiting the residual deflection of the decking soffit to span/180 but not more than 20mm. This can be increased to span/130 where the design allows for ponding.
They also recommend allowing for an increased weight of concrete where the predicted deflections are greater than 10% of the overall slab depth.
I normally allow an extra 15-25mm of wet concrete for the construction stage and limit deflections to 25mm.
Another important check during the construction stage is for beams running parallel to the ribs where the decking/fixings may not be adequate against LTB.
RE: Ponding of Concrete on Composite Steel Deck Floor
For further corroboration AISC discusses this same issue and recommends the same percentage in the composite beam design example for the 14th Ed. Design Examples on page I-9
(http://www.aisc.org/designexamples)
Ruddy, J., "Ponding of Concrete Deck Floors," Engineering Journal, V. 23, No. 3, 1986.
RE: Ponding of Concrete on Composite Steel Deck Floor
RE: Ponding of Concrete on Composite Steel Deck Floor