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Calculation x_u,lim Dutch NEN NA

There is special requirement in Dutch NEN NA (6.1(9)) for calculation of limited value of x_u,lim. In sections of beams subjected to bending without normal force - other than by pre-tensioning the height of the concrete compression zone x_u must be limited. This limitation also applies if the relevant section is loaded by a normal force - other than by pre-tensioning - less than 0.1 ∙ f_cd ∙ A_c.

Must be fulfilled the condition based on f_ck:

• x_u ≤ x_u,lim

where f_ck ≤ 50 MPa

• x_ulim = 500 ∙ d / (500 + f)

otherwise

• x_ulim = ε_cu2(3) ∙ d / (ε_cu2(3) + 7 ∙ f)

where

This calculation is done as part of the following commands

• Design of As
• Check capacity - response
• Check capacity - diagram

Design As

Limit value of x_u is set as limit for design of reinforcement.

Check capacity - response

Limit value of x_u is taken into account in calculation of check response, see Detailed output

Check capacity - diagram

Limit value of x_u is taken into account in calculation of interaction diagram, see Detailed output

Setting related to calculation of x_u

In case of Check response and Check capacity , there is a special setting how the value of compression zone is calculated. There are three options as can be seen in Concrete settings > Solver settings > Interaction diagram.

• No verification - check of x_u,lim is skipped even NEN NA is selected
• Calculation x_u based on acting load - value of compression zone is calculated based on internal forces coming from the load
• Calculation x_u based on resistances - default, it means at first the resistances are calculated using interaction diagram and these resistances are used as forces for calculation of compression zone

The information about the type of calculation is also presented in detailed output.

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