The Members | Plasticity tab is available if the "Perform advanced plastic design" check box is selected in the Members | Main tab. Here, you can specify additional settings for the partial internal forces method (PIFM).
Partial Internal Forces Method
The partial internal forces method is based on the approach described by Kindmann/Frickel [1]. The allowability of this method depends on whether the design standard permits alternative calculation methods for determining the plastic cross-section resistance and on the requirements imposed on the alternative methods. The conditions, according to EN 1993-1-1, Section 6.2.1(6), for example, are fulfilled, so that the partial internal forces method can be applied for this standard.
The partial internal forces method allows for plastic reserves to be utilized even with more complex combinations of internal forces and cross-section shapes—especially in the case of highly variable stress distributions in the cross-section. In the case of uniform stresses, however, it provides little advantage, as only small plastic reserves can be utilized.
Using Advanced Plastic Design
The partial internal forces method should be used to design “Only nonslender sections” with plastic capabilities. For testing purposes, it is also possible to analyze “All sections”.
Performing Advanced Plastic Design
There are two different methods for partial internal forces.
Partial Internal Forces Method with Redistribution
In this method, the internal forces in the partial cross-sections are redistributed. This allows thin-walled hot-rolled or welded cross-sections consisting of two or three plates to be designed: upper flange, web, and lower flange, if applicable. It is necessary to arrange the flanges horizontally and the web vertically. This method is also suitable for flat steel, tubes, and hollow sections, covering most of the cross-sections commonly used in steel structures.
Partial Internal Forces Method Without Redistribution
This variant allows you to design all thin-walled cross-sections, regardless of the manufacturing method. There is no redistribution of the partial internal forces. This makes it less efficient.
Additional Settings
The “Use constant shear stress for circular hollow sections” check box allows you to control whether constant shear stresses are taken into account throughout the entire cross-section according to [1], Figure 10.28.