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What are F-numbers? |
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Q. What are F-numbers, and what is the significance of “specified overall values” and “minimum local values?”
A. ACI 302.1R-04, “Guide for Concrete Floor and Slab Construction,” states that F-numbers define the flatness and levelness of a constructed concrete floor surface. The flatness F-number (FF) controls local surface bumpiness by limiting the magnitude of successive 1 ft (300 mm) slope changes when measured along sample measurement lines in accordance with ASTM E 1155 (Standard Test Method for Determining FF Floor Flatness and FL Floor Levelness Numbers). The levelness F-number (FL) controls local conformance to design grade by limiting differences in departure from design grade over distances of 10 ft (3 m) when measured along sample measurement lines in accordance with ASTM E 1155.
The F-number pair is always written in the order FF/FL. In theory, the range of flatness and levelness F-numbers extends from zero to infinity. In practice, FF and FL values generally fall between 12 and 45. The scale is linear, so the relative flatness/levelness of two different floors will be in proportion to the ratio of their F-numbers. For example, and FF30/FL24 floor is twice as flat and twice as level as an FF15/FL12 floor.
On random-traffic floors—those with varied and unpredictable traffic patterns—two tiers of specified FF/FL values should be indicated: one for the composite values to be achieved (specified overall value), and one for the minimum quality level that will be accepted without repair (minimum local value). Compliance with the specified overall value is based on the composite of all measured values. For any given floor, the composite FF/FL values are derived in accordance with ASTM E 1155.
Minimum local values represent the minimum acceptable flatness and levelness to be exhibited by any individual floor section. Minimum local values are generally set at 67% of the specified overall values, and are not normally set lower than 50% of the specified overall FF/FL requirements. Minimum local values should never be less than FF13/FL10, because these values represent the minimum local results achievable by any concrete floor construction method.
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Posted 2/15/06.
Disclaimer: Questions in this column were asked by users of ACI documents and have been answered by ACI staff or by a member or members of ACI technical committees. The answers do not represent the official position of an ACI committee. Only a published committee document represents the formal consensus of the committee and the Institute.
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