Improvements to the "Large panel buildings" system

The functionality of the "Large panel buildings" system is expanded. The additional parameter "design resistance of concrete in compression" in the material properties for reinforced concrete is provided. This allows you to calculate the strength of horizontal joints and panel elements of the framework according to various building codes available in the LIRA-FEM software.

The option "Unloading with initial stiffness" is added for the FE of joint.