Minimal reinforcement area (9.2.1.1(1))

The area of tensile longitudinal reinforcement has to be limited by minimal value A_s,min calculated as follows.

A_s,min = max(Coeff_As,min,2∙f_ctm∙b_t∙d / f_yk; Coeff_As,min,1∙b_t∙d)

where

• Coeff_As,min,1and Coeff_As,min,2 - values from formulas 9.1N Coeff_As,min,1= 0,26; Coeff_As,min,2 = 0,0013;
• f_ctm - mean tensile strength of concrete
• b_t - mean width of cross-section in tensile zone of cross-section
• d - effective depth of cross-section
• f_yk - yield strength of reinforcement

Calculation of tensile area of reinforcement in considered cross-section A_st.

Finally unity check is calculated as follows:

UC_9.2.1.1(1) = A_s,min/ A_s,t.

Clause 9.2.1.1(1) - Minimal tensile reinforcement for National annex

There are the following differences in particular NA.

National annex	formula 9.1N	formula 9.1N
Standard NA	CoeffAs,min,2∙fctm∙bt∙d / fyk	CoeffAs,min,1∙bt∙d
German DIN-EN NA	Not used	Not used
Dutch NEN-EN NA	max (As,min,1; As,min,2) *	-

German NA doesn’t give the limit for minimal tensile area of longitudinal reinforcement. In this case unity check is = 0.

* The procedure for Dutch NEN-NA is different. The minimal allowed value of longitudinal reinforcement is: A_s,min = max (A_s,min,1; A_s,min,2). A_s,min,1 is calculated as ULS design on three combinations of bending moment M_E,min and normal forces N_E,min. Maximal value of it is used as A_s,min,1. Additionally necessary area from ULS (A_s,req) is calculated as A_s,min,2 = 1,25 ∙ A_s,req. For more details see Theoretical background document "National annexes to EN 1992".