The non-linear calculation is activated by selecting the design method for the designs in the serviceability limit state. The various analyses to be performed as well as the stress-strain diagrams for concrete and reinforcing steel can be selected individually. Furthermore, the iteration process can be influenced by the control parameters for the convergence accuracy, the maximum number of iterations, the arrangement of layers in relation to the cross-section depth or the damping factor. 

The limit values in the serviceability limit state that shouldn’t be exceeded can be set for each surface individually, but it is also possible to define them for an entire surface group. As allowable limit values you define the maximum deformation, the maximum stresses and the maximum crack widths. When defining the maximum deformation, you have to decide additionally if you want to use the non-deformed or the deformed system for the design.

The non-linear deformation analysis is carried out by an iterative process for which the stiffnesses in cracked and non-cracked sections are taken into account. Concerning the non-linear reinforced concrete modeling, you have to define material properties that vary across the surface thickness. Therefore, to determine the cross-section depth, RF-CONCRETE NL divides the finite element into a certain number of steel and concrete layers. 

The mean steel strengths used in the calculation are based on the "Probabilistic Model Code" published by the JCSS technical committee. It is up to you to decide if a steel strength is applied that is increased until the ultimate tensile strength is reached (increasing graph in the plastic range). Regarding the concrete's material properties, you can control the stress-strain diagram for the compressive and the tensile strength. When determining the concrete compressive strength, you can choose between a parabolic and a parabolic-rectangular stress-strain diagram. On the tension side, you can either define the tensile strength according to the CEB-FIB model code 90:1993 or apply a concrete residual tensile strength to take into account the tension stiffening between the cracks.

You can choose which result values you want to receive when the non-linear calculation in the serviceability limit state has been completed:

Subsequent to the design, RF-CONCRETE NL lists the results of the non-linear calculation in clearly arranged result tables. Moreover, the module displays all intermediate values. The graphical representation for design ratios, deformations, concrete and reinforcing steel stresses, crack widths, crack depths and crack spacings in RFEM allows you to identify critical or cracked sections quickly.

Error messages or remarks concerning the calculation help you to find design problems. As the design results are displayed by surface or by point including all intermediate results, you can retrace all details of the calculation.

By exporting the input and output tables to MS Excel or OpenOffice.org Calc, the data becomes available for further use in other programs.

Due to the output's complete integration in the RFEM printout report, a structural analysis prepared for the check by test engineers is guaranteed.