Form Deck Corrosion Fix 1

[TurtleboyTom]

I have a metal deck form that has fallen apart. An engineering firm was consulted to address the building and originally their recommendation was to replace the deck. We had asked if there was any harm in removing it. They said if it considered form deck, there's no issue with removing it to just clean and coat the exposed concrete. However, others disagree with that recommendation.

Our drawings are a bit hard to decipher but here are the deck specs:

18 gage, ASTM A446, Grade A, galvanized, 1.5" depth
Epics - "Type IB30", Inryco - "Type B", H.H. Robertson "Section 3", E.G. Smith - "Peterson Types B"

Concrete thickness 6"

Above is a centrifuge and below is the flood in which the solids dump onto.

Any thoughts of suggestions on the matter would be helpful. Thanks in advance.

Support Steel

 

[jayrod12]

I don't see any reinforcing called off on that spec for the concrete. If that is the case, i.e. no reinforcing in the concrete, then you must maintain something to support the slab. The concrete alone, without reinforcing, cannot span between the beams.

 

[TurtleboyTom]

Sorry, I have a drawing showing:

main reinforcing #5@12
temp reinforcing #4@12

another drawing I have just shows the reinforcement on the bottom.

 

[phamENG]

I agree with jayrod. You need to determine what, if any, reinforcing the slab has. From there, an analysis needs to be performed to see if the slab is capable of supporting it's own dead load and the the loads imposed on it from above. 6" seems like an awful lot to just be a topping slab. It also sounds like this is in a wastewater facility? If so, they'd be crazy to rely on the deck staying in place for the life of the structure.

 

[phamENG]

Well that answers that question. The decision to allow it remain as is or replace the slab (because replacing the deck seems just this side of impossible without removing the concrete?) should be based on an analysis of the slab. I'd still want to take a core somewhere to verify the reinforcing if that's a possibility.

 

[Rabbit12]

The engineering firm recommended to replace the deck? By that do you mean the steel deck and concrete? If just the steel how the heck did they expect that to be accomplished?

 

[TurtleboyTom]

Just the metal deck, they said the concrete is in good condition.

"The floor deck has severe corrosion and metal loss, with some deck missing or hanging from the steel framing. XXX recommends cleaning the floor deck, replace, in kind, the deck that is badly corroded and hanging from the steel, then paint the floor deck in its entirety".

Then we asked it was ok to not replace in kind and they said it was fine.

Thanks to all who have replied!

 

[Rabbit12]

I'd love to hear how they think you can remove that steel deck and replace in kind.

 

[phamENG]

Interesting. You should ask them to explain how that's done. Typically, this is built by installing the beams, laying the deck across the beams (usually a minimum of 3 spans), fastening it to the beams with welds, pins, etc., laying the reinforcing, and pouring the concrete. It's possible to design a structure so the deck is permanent - it carries the dead load of the concrete, and the concrete carries the live loads and dead loads above. It's also possible to ignore the deck - make sure it's strong enough to hold the self weight of the slab, but the slab is able to carry itself and all loads above. If the latter, the deck doesn't matter and you could strip it away and nothing would happen (though I'd suggest coating the underside of the slab to protect it and the embedded steel that likely doesn't have enough cover for this application). If the former, it's dependent on the deck and the deck is dependent on its bearing on the steel beam and probably its continuity over several beams. Cut out one span, the other span(s) are weaker for it. And then there's the question of installing new deck effectively. How do you get it under the concrete and over the steel beam at both ends?

 

[Rabbit12]

I'm with pham, for our entertainment I'd like to know how they were planning to remove the deck and replace.

 

[dik]

If the concrete deck has been designed using the deck as formwork, it should be able to span without the deck. It should simply be a matter of determining what steel is required and hopefully it is less than that provided.

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik