For members with elasto-plastic sections, identical results are available as for members with standard sections: deflections, internal forces, and stresses at any point along the member length. Afterwards, elasto-plastic members can be verified and designed in Robot using calculations for steel codes.
Also, the section plastic ratio is available for members with elasto-plastic sections. It is the ratio of the area of the plasticized section to the total section area. It assumes values from 0.0 (for an elastic section) to 1.0 (for a fully plastic section). The plastic ratio is displayed in the form of maps on members.
Another option that displays results for non-linear analysis is Advanced analysis diagrams (Results menu > Advanced > Diagrams). On these diagrams, you can display the values that are assumed during the iteration process. For example, these can include diagrams of force variability or of displacements for a given point or a relationship between force and displacement during the iteration.
DEFLECTIONS
During elasto-plastic analysis, Robot calculates deflections directly within a member. A user obtains the values of displacements and nodal rotations within an internal member division. To achieve deflections at any member point, linear interpolation is performed between the points of the internal division.
INTERNAL FORCES
Internal forces in a member are calculated the same way as for linear analysis. Based on the forces and moments in the initial node and the load along the member length, Robot calculates internal forces at any point of the member.
A different algorithm is applied only for P-delta analysis. In member internal forces, the effect of the eccentricity caused by a member deflection is accounted for. Deflections are obtained at the points of member internal division.
STRESSES
In elasto-plastic analysis, normal stresses in a section are not distributed linearly. They are calculated independently for each zone. Some of the zones might fall within the plastic range; whereas, others might still belong to the elastic range of stresses. Therefore, you cannot determine unambiguously the stresses at a point along the member length.
The table (Results menu > Stresses) shows the maximum and minimum values of stresses within a section. For elasto-plastic sections, separate stresses resulting from bending and those resulting from longitudinal forces are unavailable.
Accurate stress analysis within a section of elasto-plastic members using the Stress Analysis module is impossible.