Corrosion on metal deck

[MasterB]

In a recent site observation I noticed some rusting on the underside of an existing metal deck. The existing roof system is 5" concrete(overall thickness) over an unknown metal deck thickness. Our office is taking the stance that without proper testing of the deck it would need to be replaced. There is no way we can tell how the deck will perform in a loaded condition. I am seeing resistance from the contractor on replacing the deck. The contractor is wanting to grind the metal deck, prime, and paint. Grinding would reduce the properties of the deck and without qualified personnel, if they exist, to perform the proper grinding we are in jeopardy of ruining the deck further. It is my understanding the existing roof surface will be replaced thus reducing the risk of water infilltration. Does anyone know of a product that could be applied to the underside of the deck after is is cleaned to preserve it properties, and or make it stronger. I am thinking in similarities, in concrete rennovation fiber wrap can be used. Your information will be greatly appreciated.

 

[archeng59]

is the deck painted or galvanized? how much rust? if it is surface rust, a stiff wire brush can be used to clean off the loose scale and then coat the area with a rust inhibiting paint/primer if the deck is painted or zinc-rich paint/primer if galvanized.

if the corrosion is signifant and the metal is flaking off, you could recommend removing and replacing the section that is damaged. depends on how severe the corrosion is.

based on your statement that you don't know the deck thickness, this is an existing building? any structural drawings to know if the slab is reinforced? it may be possible the slab can span without relying on the deck. the deck may be considered a temporary formwork.

 

[UcfSE]

Have you looked into bonding FRP cloth material to the deck after cleaning? I don't know if it works for metal deck but maybe a manufacturer can answer that.

http://www.fyfeco.com/

 

[MasterB]

The deck has the grayish color of the galv coating, however the amount of corrosion ( along a 10'+ length) tells us it is only painted. If the contractor were to clean it up as best as he could, and there ends up being some left over this could hurt us down the line. A chance we are not willing to take.

In this existing building, the deck is reinforced with mesh. However I am hesitant to check if the slab itself can span the gaps. We all know that the mesh gets pushed down to the bottom of the deck most times, even if we specify that it gets chaired and has the appropriate cover. From a positive moment standpoint it is helpful but what if we do not have the cover beneath the mesh and hence the development. There realy is no way to know.

Thanks for the info archeng.

 

[MMOT]

If you are confortable with the shear capacity of the concrete at the supports of the deck span, what about having them find a new piece of deck with the same profile just short of the span length and nesting it from below with the existing one (cleaned and refinished)? Then anchor it each end with either powder actuated fasteners (or welds if the existing is thick enough). I would use additional fasteners in the field of the panel for constructability and additional load transfer. I have done several renovations and the available deck profiles seem to have been pretty standard for a while...

 

[Ron]

UcfSE is right on track....consider using a carbon fiber overlay on the deck rather than replacement. Grit-blast the surface to remove rust then treat per CF manufacturer's instructions.

 

[jike]

Is this composite deck, roof deck or form deck?

 

[MasterB]

Thank you for your replies. They were helpful in working with other parts of the structure. In the end a testing lab was highered to perform an analysis (more like an observation) of the deck and found that it appeared to be in adequate condition. Thanks again.