Not quite sure how to determine the amount of profile data or how to layout survey lines for floor flatness tests?
ASTM E1155 (F-numbers) and E1486 (Waviness Index) have formulas for determining the minimum amount of data required to meet the statistical criteria of each standard. The formulae for data minimums are stated similarly, i.e. Area divided by 30 for F-numbers and Area divided by 16 for Waviness Index, but each refers to different data elements.
In the case of ASTM E1155 F-numbers, the minimum data point count refers to the number of 10 ft. elevation differences to be evaluated. This is confusing because people know the standard is based on data points that are 1 ft. apart and they assume the formula is indicating how many feet of data must be gathered. It doesn’t. For example, in a ten foot survey line of data there will be one ten foot elevation difference: the one between the measurement starting point and the end point of the line. Thus, an 11 ft. run has two; a 12 ft. run has 3, and etc. A simple way to figure how many 10 ft. elevation differences are in a survey line based on elevation data points 1 ft. apart is to subtract 9 from the number of feet in the line.
In the case of ASTM E1486 Waviness Index, the minimum data point count refers to the number of elevation points spaced apart by 1 ft. (or less). This is fairly straight forward. Since a survey line of data gathered by most test instruments like the FloorPro® is based on elevation differences (slopes), there will be one more elevation than the number of feet in the run. It’s a picket fence situation. For example, for a data spacing of 1 ft., a ten ft. long survey line has 10 spaces of 1’ each and has 11 elevation points when counting the starting position of the test device.
To comply with the minimum data quantity for F-numbers, use the formula of Area divided by 30 to determine the number of 10’ elevation differences needed. Divide that by two, to figure out how many are needed perpendicular to each other. Divide that result by the number of survey lines to be made in one direction on the slab. Then, add 9 ft. to each survey line. For example assume a 9,000 sf slab is to be tested with survey lines parallel and perpendicular to each other. Divide 9,000 sf by 30 to obtain 300 and again by 2 to obtain 150 each 10 ft. elevation differences needed in each direction. Let’s say there are 5 equally long lines in one direction and 3 equally long lines in the other. Each line in the first direction will need to be a minimum of 150 divided by 5 plus 9 ft. long, which is a minimum of 39’ long. Each line in the second direction will need to be a minimum of 150 divided by 3 plus 9 ft. long, which is a minimum of 59’ long.
To comply with the minimum data quantity for the Waviness Index, use the formula of Area divided by 16 to determine the number of elevation points needed. Divide that by two, to figure out how many are needed perpendicular to each other. Divide that result by the number of survey lines to be made in one direction on the slab. For example assume a 16,000 sf slab is to be tested with survey lines parallel and perpendicular to each other. Divide 16,000 sf by 16 to obtain 1000 and again by 2 to obtain 500 each elevation points needed in each direction. Let’s say there are 5 equally long lines in one direction and 10 equally long lines in the other. Each line in the first direction will need to be a minimum of 500 pts divided by 5 lines minus 1 or 99’ long (for 1 ft. data). Each line in the second direction will need to be a minimum of 500 pts divided by 10 lines minus 1 or 49’ long (for 1 ft. data).
Note that assumptions were made about the number of survey lines made in each direction. Both ASTM E1155 and E1486 are vague about the quantity of survey lines. Both standards require you to distribute the surveying across the slab surface so as to be blind to anisotropies and still be representative of the entire surface. ASTM E1155 requires no testing closer than 2’ to any slab termination whereas the Waviness Index specifically permits crossing construction joints. Some test agencies will test exactly 2’ from construction joints, columns, block-outs, and other slab terminations when evaluating F-numbers.
One way for a survey to be representative of the surface is to distribute survey lines across the surface so that an equal surface area is represented by each survey line. Most people will distribute the survey lines across the interior of the slab, while some test agencies will test exactly 2’ from construction joints, columns, block-outs, and other slab terminations when testing F-numbers. Some of both is recommended.
Usually the slab shape determines the number of survey lines to be used. For instance, if a 9,000 sf slab is 20’ x 450’, the limiting 20’ dimension will govern the minimum number of survey lines in that dimension. For E1155, we would calculate 9,000 sf / 30 sf/10’ elevation difference / 2 directions = 150 each 10’ elevation differences per direction. Given a 20’ dimension and the rule that no data be collected more closely than 2’ from the slab edge, there is a maximum survey line length in the 20’ dimension of 16’. Every 16’ line has (16 – 9) = 7 each 10’ elevation differences. The minimum number of 10’ elevation differences of 150 each direction divided by 7 per survey line in the 20’ dimension = 23 survey lines that are 16’ long.
It’s simpler for the Waviness Index, since there is no 2’ limiting factor and the data points required are within 1 of the line length in feet. Given a 16,000 sf slab that is 160’ x 100’ and dividing the area by 16 and again by 2 yields 500 elevation points required in each direction. For practical purposes let’s say the survey line length will be shorter than the width or length of the slab. For instance in the 100’ dimension assume 75’ long survey lines (with 76 elevation points per line). 500 divided by 75, rounded to the nearest whole number = 7 survey lines. For simplicity’s sake you could use 75’ long survey lines in both directions for a total of 14 survey lines for that slab.
It’s obvious any number of survey line lengths and survey lines can be used to measure the surface flatness of a given slab. The bottom line is that if there is any question of the results obtained, gather more data. There is no upper limit on the amount of surface profiling for a slab for either ASTM E1155 or ASTM E1486.