Why do I need the RF‑CONCRETE NL add‑on module for the stability design in RF‑CONCRETE Members? EC 2, Section 5.8.6, only speaks about geometric nonlinearity.

Answer

For the stability design of compression elements, you need the combination of RF‑CONCRETE Members and RF‑CONCRETE NL. The reason is the following:

First, the internal forces of the individual load combinations (second-order analysis + imperfection) are subjected to the linear-elastic calculation. For this, you basically only need RFEM.

Then, the cross-section design is performed in RF-CONCRETE Members with these internal forces determined linearly-elastically, and the required bending reinforcement is determined from these internal forces.

This bending reinforcement is then compared with the user-defined entries concerning the existing basic reinforcement or the minimum reinforcement and based on this, the reinforcement concept is generated (dialog box "3.1 Existing Longitudinal Reinforcement" of the module).

This existing longitudinal reinforcement is then used for the nonlinear design.

According to Section 5.8.6 (1), geometric nonlinearities must be taken into account according to the second-order analysis. However, the general rules for nonlinear methods according to 5.7 also apply.

In Sec. 5.7(1), "an adequate non-linear behaviour for materials is assumed." According to 5.7(4)P, the use of material characteristics which represent the stiffness in a realistic way but take account of the uncertainties of failure shall be used when using non-linear analysis.

This requires the RF-CONCRETE NL add-on module. Thus, the geometric and material nonlinearities are considered and the requirements of EC 2 regarding the ultimate limit state design are fulfilled.

Similarly, this method is also available in RSTAB in the CONCRETE add-on module.

Keywords

members compression general method nonlinearity stability design

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