Fold line location determination

The determination of the shape of a fabric form under hydraulic pressure requires the resolution of an equation with five variables. The solution is found recursively and can be seen in the image below where the height of the concrete footing (12") is found in over 5,000 lines of the Excel spreadsheet. In this case the contact width is 8". The spread sheet calculates the fabric upper length of 22.18". The bottom edge of the ICF block is located at 0 on the "X" axis and 12" on the "Y" axis.

Hoop tension in fabric

The Excel program also determines the hoop tension in the fabric induced by the hydraulic pressure of the concrete (in this case 4.848 pounds per lineal inch of fabric). If the fabric is attached with a plywood batten with screws 8" on centre, the pressure on each screw will be 4.848 lbs. x 8" = 38.8 lbs., well within the pullout strength a screw in a typical ICF web.

Monopour lift heights

In the example shown below, the height of the concrete poured into the stem wall is 15.5", 30% greater than the footing height of 12". When monopouring it is extremely important that the first lift fills up the footing and part of the first block, and the concrete is then allowed to "go-off". If the concrete height is excessive and if vibration is encouraged, the concrete in the wall will attempt to blow up the bag and lift the form. You can easily see when this is about to occur as the angle of the fabric by the plywood batten will be greater than 90 degrees.

If you wish to download the Excel spread sheet, click on the image below.

Excel calculator

Concrete consumption

As can be seen in the curve in the image below, concrete is wasted in the bulge area, and saved by in the sloped region on the upper edge of the footing. Concrete is also saved as you pour into a closed form, hence no leakage. When ordering concrete it is best to assume concrete consumption is the same as with a rectangular shaped footing.

Cross section of monopour