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F-Numbers or F-Min System

1. What is F-min?

F-min is the superflat floor industry standard measuring system for very narrow aisle (VNA) Defined-Traffic floors. It is expressed as a unitless number for both the Longitudinal and Transverse axis for an exact wheelbase configuration of a given VNA forklift truck or order picker crane in high-stack warehouses, and the higher the number, the more flat and level the floor. An example of this tolerance is expressed as follows: F-min L 85/F-min T 100.

The primary reason for developing the F-min system was to quantify the threshold of mast sway for preventing lift truck payload racking strikes and analyze the bumpiness of VNA floors. The system allowed contractors to expedite floor repairs and ultimately paved the way for the fresh method of construction techniques to manufacture this type of floor and spawned a new breed of specialty contractors to better the installation of such high tolerance floors.

Because a VNA lift trucks wheel path does not vary in its movement down and aisle from side to side, it's important to measure the exact path that the lift truck will travel. Unlike the measurement criteria for the FF/FL or Random-Traffic system, F-min measurements are taken by a vehicle (lift truck) simulator that tracks the exact wheel paths the actual lift truck follows in an aisle. This proprietary measuring device, the F-min Profiler™, is a digital, semi-continuous recording dual-axis differential profileograph. The data from the profileograph formulates the F-min calculations to render a certification of compliance or report any noncompliance indicating the location of required remedial activity (grinding areas). Floor defects in the wheel paths that cause sudden changes in floor level is actually a flatness anomoly (Slope Defect) and over time will result in catastrophic truck failure such as broken mast welds, mechanical breakdowns, lost loads, conflicts between machine and racking, floor damage, wheel damage, bearing failure, hydraulic leaks, etc. etc. the list goes on. Simply put, a Flat floor saves money and an inferior floor causes many problems.

2. How is F-min better than FF/FL for VNA floors?

Although ACI 302 states floors are classified as a Superflat floor as generally meeting or exceeding FF 50/FL 50, it's important to note that the use of the FF/FL system will not guarantee trouble-free operations for VNA lift trucks. This is because the FF/FL system measurements are random 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 path 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.

3. Why is there a need to be so accurate with floor flatness on superflat floors?

The short answer is: to save time, to save money and improve productivity. Architects, engineers and the operations managers of new construction and existing distribution centers or warehouses often overlook the concrete floor as a means of saving money and daily operating costs. After all, it's just concrete - right?

On the contrary! Successful distribution center and warehouse operators will tell you that the most effective wheeled vehicle material handling system is one that is based on floors that have superior flatness and levelness. For any VNA operation, having a Superflat floor becomes even more important as rack heights increase and/or aisle pathways narrow to house more racks.

When rack height increases and narrows, the risk of rack to lift truck conflicts increased due to the lift truck leaning to one side and a seemingly insignificant bump or dip in the floor can cause major problems. A bump as small as 1/8th-inch in the floor means the mast will lean about 6 inches at 60 feet in the air. Add this to the dynamic flexing of the frame, or fishing pole effect combined with the speed of the lift truck and the inertia and the results are disastrous.

Extraordinarily flat level floors provide for quick and immediate access to inventory, proven by the FEM equation for single and double cycles, and they provide a measure of operator safety with regard to lift truck operations. If the lift truck operator must slow down for each bump they encounter in file, this translates into lost productivity and lost money.

Achieving maximum lift truck performance and machine utilization depends directly on floor flatness and levelness. The flatter and more level the VNA floor, the less problems one will encounter an overall material handling operations. In addition, many lift truck manufacturers will not warranty their equipment against mechanical failures the intended floor that the truck will operate on does not meet the required F-min tolerances. ACI 360-10 shows a list of F-min Toleances for such lift trucks.

Now let's talk about vehicle maintenance. Can you imagine what would happen to your car if you drove to work and it was on the road 24/7/365? Imagine your car with no suspension (rigid) and there are potholes in the road everywhere. Now drive for speed, hold on and put your mouthpiece in and protect your teeth. That is what it is like to material handling equipment (MHE). Many of these warehouses run on three overlapping shifts and the trucks do not get a break, except when they are broken and the shop for repair or refueling. Downtime cost is very, very expensive and the flatness component of an F-min floor is the tolerance that is responsible for vehicle chassis problems. This smoothness or bumpiness of the floor, whichever it is, can make or break a facilities throughput.

4. How does the F-min system work?

Four separate floor measurement characteristics make the F-min system. It's expressed as a two number system (e.g. F-min L 65/ F-min T 85) but actually has four components:

F-min L tolerance band consisting of;

Longitudinal levelness

F-min T tolerance band consisting of;

Transverse levelness

F-min L rate of change within 12 inch intervals

Longitudinal flatness

F-min T rate of change within 12 inch intervals

Transverse flatness

Longitudinal refers to the long axis of the aisles and truck and the relationship and rate change between the front and rear wheels of the lift truck. Transverse refers to the side-to-side relationship between the right and left side of the vehicle that either the front or rear sets of wheels, but more predominantly the fork and/or picking and of the vehicle for the mast is positioned, also known as the load end.

5. How do bumps or dips in a VNA floor affect lift truck operations?

In the following table, the effects of seemingly insignificant floor height discrepancies clearly show the amount of mast lean a forklift will encounter while at rest. This is called static lean, which is one front wheel resting on top of a known defect of the size indicated. The bump or dip creates lift truck static lean as shown here in this table below:

48 inch front wheel with lift truck

side to side wheel elevation difference resulting in static lean from the theoretical vertical position: ((insert chart))

in addition to the above static lean values, the added effect of dynamic flexing or the dynamic lean fishing pole effect is the static lean multiplied by a factor of 3 to 5 (caused by inertia) to the frame and mast clearly show the potential for disastrous results. In short, the relationship between mast height, aisle width, size of the floor defect, and inertia determine the F-min requirements for a particular lift truck application. The following table identifies the F - min tolerances for typical rack heights: ((insert chart))

6. Since I have been meeting FF/FL standards for years, what kind of problems will I face with an F-min floor?

The factors affecting superior floor finishing are too numerous to list here. But, we can truthfully say that although F-min may sound intimidating at first, it's really not any more difficult than any other high-quality floor finishing procedure. The difference is tolerance control all along with the correct tools and techniques, which are totally different from Random-Traffic (FF/FL) applications.

You should consider hiring a competent and well experienced consulting firm such as ALLFLAT to help you through the first few F-min pours. We will be there to personally guide you through every step of the process from the pre-construction meeting to the floor measurement certification. After that, you will be an expert in the forming, placement, and finishing of F-min floors.

7. What if the floor does not meet the F-min specification?

The “what ifs” need to be addressed long before construction begins. Typically, successful effort and floor contractors have several discussions with the project decision makers regarding for specifications, anticipated problems, and remedy plans in the pre-construction meetings. After all, concrete is a dynamic media and things do happen. Having discussed the “what-ifs” beforehand, makes life much easier for all parties involved.

If a particular slab is out of tolerance, there are a few available options. These range from corrective spot grinding and a full aisle grinding, to removal of the discrepant floor and replacing it with a new slab. All of these operations should be discussed and well understood by all concerned parties prior to beginning construction of the F-min slab. But, it is our experience that the vast majority of the F-min contractors have less than 10% discrepancies in their slabs and may have 0 to 5% discrepancies.

8. So what's wrong with the old straight-edge specifications?

There is a general disagreement and what exactly 1/8th-inch in 10 feet means. Does it mean that you can only have a gap of 1/8th-inch anywhere under the straight edge? Or, does it mean that there can be a gap of plus or minus1/8th-inch anywhere under the straight edge? If it's the latter then in reality, there is a ¼-inch tolerance band around the theoretical perfectly flat plane that is horizontal. In addition, the question of “where to measure” complicates the matter. What if the floor is good in one direction, but not in the other direction? Grinding down one area may make the floor appear better for that spot in that direction, but one could have just made the opposite side of where the trouble was with respect to its chassis length twice as bad on the other side. Confusing isn't it?

Let's say we inspect the floor along the side of the form, and it passes. But, if we turned the straight edge 45° to 90° and the floor fails in that direction, what then? In short, the straightedge technique is unscientific, unpredictable, unreliable and non-repeatable. Two different people can get two different results on the same floor with the same tools. To further complicate things, there is no standard way of testing a floor using a straight edge; so who is right and who is wrong? In short, this method is just not practical for VNA measurement applications. And who wants to crawl around on the floor with a straight edge for hours, days or even weeks anyway when one can run the F-min Profiler™ and get it done in minutes!

Although the straightedge method is still in use and has been for an unknown number of square feet of concrete construction, the typical flat work slab rarely meets the 1/8th-inch requirement anyway. In reality, floor slabs measured with electronic instruments indicate the measurements are more like 5/8 inch than 1/8 inch.

9. If the straightedge method is so inaccurate how, how can you measure VNA defined traffic floors?

For the past three decades, great strides in improving the accuracy of concrete measurement techniques continue to increase measuring accuracy. For VNA defined traffic floors, the simplest way to verify that a floor will not lead to lift truck failure or racking conflicts is to use the ALLFLAT F-min Profiler™.

The F-min Profiler™ is a robotic, electronic dual-axis differential profileograph that measures both the elevation difference between the left and right front wheels and the difference between the front wheels and the rear wheels simultaneously! Plus, at the end of the run, the results are available instantly. No waiting around for hours or days to have tapes analyzed or data sent off to someone so that they can imported into a spreadsheet to provide you with profiles of numbers that make no sense. Simply read the results right on the computer screen indicating compliance, or grind off the marks the machine automatically delineated on the floor while autonomously measuring the aisle. It's that simple!

This feature is a revolutionary concept for measurement because it allows the placement and finishing crew to get immediate feedback on the quality of their work and allows them to make appropriate changes for the next concrete pour to improve the quality of the floors whereby significantly increasing Superflat slab production. Just ask some of our clients for a testimonial for confirmation.

10. What good does it do to find out after the slab is poured? Isn't it too late?

The F-min system is not intended to be a witch-hunt to lay blame. Rather, it's used as a tool for improvement. It's been our experience that when finishing crews realize how good they can make a floor, they tend to challenge themselves to do better and try to achieve higher F min numbers on the next pour. These measurements keep the spirit of competition alive; consequently, providing a superior floor for the client and increasing the chance to the contractor to win a Golden Trowel™ award.

Typically, we make F-min measurements at the end of the hard trowel work. The results assist with making the appropriate decision to correct any errors to keep them from being repeated on subsequent pours. After a few times of working with us, most contractors feel at ease when bidding on an F-min project because they have first-hand knowledge of fishing practices that lead to superior flat and level floors.

11. That's great for the second pour and subsequent pours, but what about the first pour?

Contractors have come to rely on ALLFLAT Consulting to assist them with ensuring that every detail of the concrete flat work project is in accordance with proven F-min finishing techniques. We can assist you with everything from planning your next bid proposal to providing advice on finishing techniques. Our team of professionals have decades of concrete fishing experience and can tell you exactly what to do in order to achieve the highest possible F min results for a particular application.

12. How can I find out what kind of F-min floors I have been producing?

It's simple - call us for a consultation appointment and arranged to have us come out to measure some of your exitsting floors or concrete placements for evaluation. The results are immediate and there is no waiting for report. We can tell you right there on the spot what you are or are not achieving and why.

13. How long does it take to measure a VNA defined traffic aisle?

The answer depends on the length and width of the slab and the number of VNA aisles for that slab. Typically, a slab that measures 15 feet wide by 350 feet long takes about 15 minutes to measure. Add to that another 30 to 45 minutes to allow for setup and breakdown of our measuring equipment. But most importantly is the fact that you do not have to wait for the results. At the end of the aisle the machine displays results instantaneously and again; any out - of - tolerance anomalies were marked automatically while profiling.

14. What happens if the floor doesn't meet the F min specification?

That question needs to be answered long before we measure the floor. Ideally, we would have one of our team members present at the concrete placement preconstruction meeting to advise the interested parties on corrective action options. This way, if there are any discrepancies in the slab, there'd be no delay in making a decision for corrections to bring the slab into F-min compliance.

15. What are the corrective action options for F min discrepancies?

Most often, remedial grinding of the out-of-tolerance area(s) is the way to bring a floor back into tolerance. The F-min Profiler™ marks the floor exactly where the out-of-tolerance area(s) need grinding. Upon completion of the measurement run, remedial spot grinding of the freshly placed concrete brings the aisle back into tolerance with little or no lost time. Another method is the application of a topping or covering material to the concrete however, it's been our experience that these methods tend to amplify the problem because of improper installation or overtime (six months to three years) the toppings failed and begin to delaminate and pop out or blister and peel. This causes major problems with material handling equipment (MHE) and drastically increases downtime. Once this happens extremely expensive alternatives have to be performed to get the floor flat and level.

16. How do I get more information on VNA defined traffic floors?

ALLFLAT has a team of professionals on staff to assist you in many ways. Simply call our Toll-Free number 877–ALLFLAT and speak to one of our experienced staff about your next project. We are here to help you make sure your world is FLAT!

Digital Profileograph measuring F-min in existing problematic warehouse