Conform deck upside down 1

[AJC3636]

Had a contractor install the deck for a platform upside down. The deck has 4.5 “ on concrete on it to make a 6” total thickness. He is using 1.5C vulcraft confirm deck. Essentially it is just a form, correct? Doesn’t really matter after it is cured.

Am I missing anything? Any other considerations?

 

[DTGT2002]

Without pulling the specification for the product, their are typically small differences in sectional properties by orientation, but that would impact the design for installation and form use. Since your slab design did not count on the form deck for anything, there should be no consequence, though it would be prudent to verify there are no unanticipated exposed edges or openings where the layup of the deck started or ended.

 

[SlideRuleEra]

The deck has 4.5" on concrete on it to make a 6” total thickness. Essentially it is just a form, correct?

The properties (moment of inertia, section modulus) of the steel deck will be the same, but consider how the concrete is shaped by the deck corrugations in both cases.

When right-side-up, about 2/3 of the concrete is 6" thick:

When upside-down, half that amount (about 1/3 of the concrete), is 6" thick:

Is that difference significant? IMHO, it depends... review the concrete mix design used, especially the size of the coarse aggregate. If the coarse aggregate is "large", compared to the size of corrugations that contact supports, there may be reason to take a closer look.

http://www.SlideRuleEra.net

 

[BridgeSmith]

It would seem to me that it would depend on whether the design counted on the section properties of the actual slab with the form right-side-up, or if the slab is adequate ignoring the concrete in the form.

When we use similar forms for bridge decks, they're oriented in what SRE shows as the "Upside-Down" position, usually with foam filling half or more of the flutes to keep the weight below what we accounted for in the design of the bridge. Of course, we ignore the contribution of the additional section depth to the structural capacity.

 

[rapt]

It will affect your deflections. Did you ignore the deck and the concrete loss in the original design, assuming that the slab was the full 6" thick? If yes, you have underestimated the deflections.

Now with it upside down, deflections will be even worse with the extra concrete loss.

 

[Celt83]

To expand on SlideRuleEra's sketches where did the reinf. end up?

Open Source Structural Applications:

https://github.com/buddyd16/Structural-Engineering

 

[Agent666]

If its a composite slab (deck is part of the permanent slab reinforcement) then I think it would definitely be an issue. But looking at the profile on the manufacturers site I believe they only classify it for non composite slabs. So I think its fairly safe to assume its been designed as a non composite slab. Whether this means the deck is the final structure with no additional reinforcement, or if additional reinforcement was provided and the deck was essentially only a permanent form would obviously require clarification from whomever designed it.

If its the final structure then the properties bending one way could potentially be different than the other way due to slenderness of longer sections being in compression instead of tension. However I guess because the deck is usually installed in continuous runs there are areas both in +ve and -ve flexure so perhaps this is accounted for in the published capacities. Best to run it past the supplier of the deck as they will be in the best position to comment on any issues. Usually the critical case is during concrete placement at the supports where combined bearing and flexure are the critical limit state base don my experience with other deck profiles (having bearing on the opposite narrower face to may impact on this check).

If its upside down and its was a profile meant for composite slabs then all the little stiffening elements typically present in the deck are essentially inverted so the mechanical bond to the slab concrete would be affected.

Fire performance is something else that would potentially be affected which has not been mentioned by anyone else. Totally depends on where the reinforcement ends up like Celt83 noted.

 

[JLNJ]

If you have heavy wheel loads you might be losing some shear capacity near the supports. It also might be a little harder to make the deck-to-beam connections with the upside down deck due to the narrow flutes (doubly true if shear studs are involved).