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RF-CONCRETE Members Version 5

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2.2.3 Minimum Reinforcement

Minimum Reinforcement

The minimum reinforcement area for crack control is determined according to EN 1992-1-1, clause 7.3.2 (2), Eq. (7.1), simplified as follows:

As,min · σs = kc · k · fct,eff · Act  

Equation 2.10 (7.1)

where

    • As,min : minimum area of reinforcing steel in tension zone
    • σs : allowable stress of reinforcing steel according to Figure 2.3
    • kc : factor for considering stress distribution in tension zone
      • kc = 1.0 for pure tension
      • kc = 0.4 for bending
      • For bending with axial force, kc is determined as follows:

kc = 0.4 · 1 -σck1 · h/h* · fct,eff  1

Equation 2.11 EN 1992-1-1, Eq. (7.2)

    • where
      • σc : mean concrete stress acting on part of section under consideration, σc = NEd / (b ⋅ h)
      • NEd : axial force acting on part of cross-section under consideration
      • h* : = h < 1.0m
      • k1 : coefficient for considering effects of axial forces on stress distribution:
          • k1=1.5 for NEd = compressive force
            k1 = 2h*/3h for NEd = tensile force
    • k : coefficient to consider nonlinearly distributed self-equilibrating stresses
      • k = 1.0 for webs with h ≤ 300mm
      • k = 0.65 for h ≥ 800 mm
      • k = 1.0 for restraint caused outside (e.g. column settlement)
    • fct,eff : mean value of effective tensile strength of concrete when cracks occur
    • Act : area of concrete tension zone
Figure 2.3 Limit diameter Øs* for reinforcing steels according to EN 1992-1-1, Table 7.2

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