huangyhg

concrete specs & floor flatness
does anyone have any advice on specifying floor flatness for unshored elevated slabs in general office buildings? what is the difference between overall values of flatness and levelness vs. local value of flatness and levelness? i am specifying f(f)=25 & f(l)=20 for overall value...what should i specify for loca values? & is anything really specified for levelness in an unshored slabs?
there will be guidelines somwhere in your area which will give you indications of tolerance in building works.
in the uk bs5606:1990 guide to accuracy in buildings might be of some use. flatness of in situ floors is usually around 5mm deviation over a 3m length but you need to check what is acceptable for you location.
in addition you would find guidance in the national structural concrete specification for building construction (isbn 0 7210 1571 9). section 7 covers construction accuracy with things like twist, squareness, position, level, verticality, bow etc. again this is a uk document but i would imagine there is something similiar in you area.
this should help:
also see:
aci 302.1r "guide for concrete floor and slab construction"
aci 117-90 "standard specifications for tolerances for concrete construction and materials"
further to the aci & astm references above you can go to faceco.com/40q.htlm (40 most asked questions about f numbers). this was put together by face company who make profile surveys and/or equipment to do so. i have not used them or their equipment, but they seem to know a lot about it.
i do know that trying to obtain an overall value of ff25/fl20 is very hard (as our spec is the same) and the local labor here never achieved it. as a consequence we are going to have to do a lot of grining and filling to satisfy the client.
unless you are very certian about your contractor's capabilities you might want to consider lowering the slab a bit and using a self leveling topping.
special care must also be taken to fully understand what you are specifing. there is a certain timespan in which to complete the flatness testing. the design must be sufficient to account for creep and shrinkage and natural settlemet - things that the contractor cannot necessarily be blamed for. if the slabs are elevated, the construction process can influence the flatness and do note the typical finish tolerances are as cast prior to the slab carrying its own weight. do review testing procudures to ensure the slab you design and specify will be adequate for the final use.
contractors and suncontractors who specialize in such formwork and placement are often much more aware of when why and how a slab is to be tested. if your specs or methodology is questioned, do make sure you understand why you are specfying such numbers.
best of luck,
daniel toon

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