Deduct intersections in a supplied concrete rib grid.
Why is the sum of two directions of ribs larger than the actual material?
Use the matching calculator
Use this decision sequence
- Calculate the continuous top layer over the entire footprint.
- Measure rib depth below that layer, not total top-to-bottom thickness.
- Add the volume of each specified full-length rib direction.
- Deduct the common volume at every crossing once before combining with the top layer.
Keep the quantities distinct
| Quantity or assumption | How to use it |
|---|---|
| Top layer | Continuous area times top thickness. |
| Two rib directions | Include their crossing volumes twice. |
| Crossing deduction | Number of crossings times both widths times below-top depth. |
Worked comparison
A 4 m by 3 m top layer at 0.1 m contains 1.2 m³. Two 0.2 m-wide ribs in each direction, 0.3 m below that layer, add 0.48 + 0.36 = 0.84 m³ before deduction. Four crossings each contain 0.2×0.2×0.3 = 0.012 m³. The reconciled total is 1.2 + 0.84 − 0.048 = 1.992 m³.
Check before using the estimate
Counts, sections and layout must be supplied by the existing design; quantity does not demonstrate structural suitability.
All dimensions, product properties, prices and specifications in this example are illustrative arithmetic inputs. Use the values from your measured plan, selected product data sheet and supplier quote. This guide does not choose construction specifications or certify safety.
Calculation and scope checked 2026-10-04. Methods and scope.
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