Concrete cover c
The concrete cover c is to the axis of the bottom wire.
Total length L
The total length is the net calculation length – axis to axis.
Age concrete is when the top layer is poured, supported by the strut.
Extra load q
The extra load is set at a value of 1 kN/m², see art. 188.8.131.52.3 of NBN EN 13747, the European standard for precast floor plates. The Belgian national annex to the European standard, NBN B 21-606, increases this value to 2 kN/m². Belgian wide plate manufacturers all use a value of 2 kN/m² for the determination of strut spacing. Dutch manufacturers calculate with a lower value, usually 1 kN/m²