Normal Forces (Stiffness Change)
In the case of a non-linear solution (p-delta effects, large displacements) the superposition of load cases is theoretically not allowed. The normal forces used for the calculation of the stiffness matrices must therefore represent total states. It is therefore necessary to define an initial state of the normal force distribution in the system, if differential loading cases are investigated. This might be done for single Load Cases by specifying these initial normal forces as a Load Set assigned to the Load Case to be calculated.
For these Load Sets the following two load types are available:
Assign normal force directly (just stiffness) – load type PDFOR
| Load Type | Description |
|---|---|
| PDFOR | Direct assignment of a user defined normal force intensity to an element series |
This load type allows for assigning arbitrary user defined normal forces to any elements of the structural system (Fx internal normal force in kN). These normal forces are not applied as a loading inducing deformations of the structural system, but as initial values influencing the stiffness of the respective elements in calculations taking into account P-Delta effects. This allows for performing geometrically nonlinear analyses also for differential load cases.
Assign normal force from LC (just stiffness) – load type PDFLC
| Load Type | Description |
|---|---|
| PDFLC | The normal force is read from the load case results pool and assigned to the appropriate element series. |
This load type allows for assigning normal forces due to previously calculated load cases to any elements of the structural system. These normal forces are not applied as a loading, inducing deformations of the structural system, but as initial values influencing the stiffness of the respective elements in calculations taking into account P-Delta effects. This allows for performing geometrically nonlinear analyses also for differential load cases.