F min numbers (ACI360R-10)

* Free Movement

First used on a large-scale commercial project in 1983, the F-number system for measuring floor flatness (FF,) and levelness (FL), then had been perhaps the most significant factor in enabling the construction of flatter and more level (horizontal) concrete floors. However, because the dimensionless F-numbers are derived by processing the data from a large number of measurements, it can be difficult to grasp exactly what it means.

* Defined Movement

The most practical way to measure a defined movement floor is by making continuous measurements of each aisle. Such direct measurement will usually involve point separations other than 300mm or 3000mm. FF and FL cannot be used since they are random measurements across the entire slab. There is a great probability that significant floor defects in the wheel path will be missed; furthermore, if one did measure each individual wheel paths with a random traffic measuring device the results are an average at best and F-min cannot be averaged. Therefore, there is no direct correlation between FF/FL and F-min. The FF/FL and F-min systems are completely different measuring systems and there is no corresponding index for comparison purposes. A single F-number “F-min” is therefore used to define the worst acceptable flatness and levelness conditions in a VNA aisle, and this F-min value is assigned based on the expected lift truck and rack height.