 # RF-CONCRETE Surfaces – Online Manual Version 5

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# 2.6.4.7 Limitation of concrete compressive stress

#### Limitation of concrete compressive stress

In window 1.3 Surfaces, the concrete compressive stress is limited to σc,max = 0.45 ⋅ fck and the steel stress to σs,max = 0.80 ⋅ fyk.

For concrete C30/37, the maximum (negative) concrete stress σc,max is thus determined:

• σc,max = 0.45 ∙ fck = 0.45 ∙ (-30.0) = -13.5 N/mm2

The provided concrete compressive stress is determined under the assumption of a linear stress distribution because the multitude of iterations for determining the suitable direction of the concrete compression strut would be too time-consuming. A linear distribution is sufficiently accurate because in the serviceability state, there are normally concrete compressive strains of at most 0.3 to 0.5 ‰.

The maximum stress σc,max is to be compared with the provided stress of the concrete compression zone for both reinforcement directions.

The provided concrete compressive stress σc is determined as follows:

where

 mEd applied moment ideal moment of inertia in state II b width of element (always 1 m for plates) αE ratio of elastic moduli as provided tension reinforcement d effective depth depth of concrete neutral axis

For the reinforcement direction φ1, the following neutral axis depth x-z,φ1 is thus obtained:

The same value and the related intermediate values can also be found in the details table.

For the reinforcement direction φ2, the neutral axis depth x-z,φ2 is obtained:

This value and the related intermediate values can also be found in the details.