Concrete slab form work removal with limited vertical clearance
Concrete slab form work removal with limited vertical clearance
(OP)
I am working on a concrete platform project that may have a construction issue due to the limited vertical clearance available to remove the form work for the proposed cast-in-place (CIP) slab. The slab will be between 12 ft to 25 ft in width and the span length varies between 10 ft to 20 ft in length. Currently, there is a 4'-3" minimum vertical clearance available under the slab.
Does anybody know the minimum vertical clearance required for form work removal? Would 4'-3" be sufficient?
Many thanks!
Does anybody know the minimum vertical clearance required for form work removal? Would 4'-3" be sufficient?
Many thanks!






RE: Concrete slab form work removal with limited vertical clearance
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RE: Concrete slab form work removal with limited vertical clearance
RE: Concrete slab form work removal with limited vertical clearance
RE: Concrete slab form work removal with limited vertical clearance
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RE: Concrete slab form work removal with limited vertical clearance
RE: Concrete slab form work removal with limited vertical clearance
IMHO, there is no such thing as a "standard" form. A Contractor looks at this type situation differently than an Engineer:
The Engineer typical investigates cost effective form design. The Contractor does this, too... but the economics are different. Each Contractor's approach will vary.
The Contractor views form design "backwards". That is, "How do I design the forms to make use of materials that I already have (in other words, materials that are 'free')?" The Contractor's result is often different and innovative. An Engineer would have ruled out a Contractor's proposal as not economically viable.
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RE: Concrete slab form work removal with limited vertical clearance
RE: Concrete slab form work removal with limited vertical clearance
Access after casting the slab is critical. You say the slab is supported by walls - if the perimeter walls have no openings, how does one get the formwork out?
Ralph
Structures Consulting
Northeast USA
RE: Concrete slab form work removal with limited vertical clearance
RE: Concrete slab form work removal with limited vertical clearance
I agree with Teguci that lost in place forms may be the way to go. My experience is that these are frequently cheaper since there are no stripping costs. And what you could strip from your project likely wont be salvageable.
The piers on the Dumbarton Bridge in CA are still full of wood and plywood forms that I designed.
RE: Concrete slab form work removal with limited vertical clearance
We considered using metal deck forms to leave the forms in place, but the options are limited for the 20'-0" spans. The cost as Teguci said is much higher, about $14/sq.ft vs. $2/sq. ft for shorter spans. However, we also have an area that will require a 40'-0" span and will need to be cast-in-place (with the 4'-3" vertical clearance limitation as well).
RE: Concrete slab form work removal with limited vertical clearance
RE: Concrete slab form work removal with limited vertical clearance
fsosa - You haven't mentioned the slab thickness. Is it a flat plate or are there beams involved (concrete or steel)?
Leaving the forms in place will involve more than just the plywood. I really do not see a problem with clear height under the slab, although I personally wouldn't enjoy stripping out the formwork. As far as being able to see the underside after construction I don't see this as being any different than a slab on metal deck. You can't observe the integrity of a slab on metal deck after construction.
Ralph
Structures Consulting
Northeast USA
RE: Concrete slab form work removal with limited vertical clearance
RE: Concrete slab form work removal with limited vertical clearance
fsosa - This certainly would not be formed with plywood plus a few posts. I would expect that the plywood would be supported by joists 12-16" c/c. The joists in turn would be supported by stringers at perhaps 48-72" c/c, and the stringers supported by posts at an appropriate spacing. The posts would have to bear on mudsill/mudpads whose size would depend on the soil conditions. Spacings of course would be determined by the actual members' material and size. Certainly a lot more material than anyone would want to abandon in place.
Perhaps the use of geofoam blocks might be appropriate if no subsequent access under this slab is anticipated. Provide a reasonably graded/leveled base and fill the space with geofoam blocks.
In either case, the owner will be paying for the material used or abandoned.
Ralph
Structures Consulting
Northeast USA