# What is the purpose of the function "Design of longitudinal reinforcement for percentage of utilization" in the setting for nonlinear calculation in RF‑CONCRETE Members? I have selected this option but the structural system is unstable anyway. Why?

This option is only effective if the utilization of 1/γ > 1.000 results in the NL calculation with the existing longitudinal reinforcement (resulting from the statically required reinforcement, linear analysis) or preset basic reinforcement.

If you select this option, the required reinforcement or specified basic reinforcement is increased accordingly to achieve a ratio < 1.00 for the NL calculation. However, this option only works for cross-section design (NL utilization 1/γ > 1.00, see the result window 6.1.1, Column E).

Important: If there is a stability problem (message => structural resistance not sufficient, for example, a stability analysis of a column according to the second-order analysis), this option does not help. In this case, it is necessary to specify the reinforcement manually or adjust the structural system / load.