From the design moments the required bending reinforcement in x- and y-direction are calculated according to [2] 3.1.7 and 6.1 with a stress-strain condition according to the below figure.

• λ = 0,8 and η = 1 for f_ck < 50 MPa
• λ = 0,8 - (f_ck / 50) / 400 and η = 1,0 - (f_ck - 50) / 200 for 50 < f_ck < 90 MPa

The value of the design compressive strength is defined as:

f_cd = α_cc f_ck / γ_c

α_cc = 1,0

γ_c is the partial safety factor.

 British annex

α_cc = 0,85

 Finnish annex

α_cc = 0,85

If the design moment is larger than the moment corresponding to balanced reinforcement required compression reinforcement is calculated.

Minimum reinforcement area

Minimum tensile reinforcement in the main direction should according to [2] 9.3.1.1 should not be less than:

A_s,min > 0,26 f_ctm / f_yk b d > 0,0013 b d

where

• b is the width of the slab perpendicular to the reinforcement direction
• d is the effective depth of the slab in this direction.