In the Stiffness Analysis Configuration dialog box, you can define basic specifications for determining the stiffness of a steel joint. The specifications are applied to a submodel that is created in the background for the calculation.
A "list" on the left shows all configurations available in the model. Use the
button to create a new configuration based on the default values of the design standard spacified in the
Base Data
. As an alternative, you can copy the existing configuration by using the
button and then adjust the design parameters. The
button deletes the configuration selected in the list.
Main
The Main tab manages important "Design Parameters" for the stress analysis.
Stiffness Analysis Type
Define whether to determine the 'Initial Stiffness' Sj,ini or to create a 'Stiffness Diagram' ( in preparation ).
Joint-Structure Interaction
The "Generate hinges in global model" check box provides the option to apply the stiffness analysis results in the RFEM model in the form of member hinges. RFEM creates hinges with the spring stiffnesses of the joints and assigns them to the members.
Classification by Stiffness
The "Frame with bracing systems" check box indicates a bracing system that reduces the horizontal displacement by a minimum of 80%. By selecting this option, you can ultimately influence the coefficient Kb, which is then only 8 instead of 25.
Analysis
The Analysis Type list provides a selection option between the geometrically linear analysis and the second-order analysis (PΔ).
If the calculation does not converge in the case of the default setting of the maximum of 100 iterations, you should increase the "Maximum number of iterations" accordingly. Further information can be found in Chapter Static Analysis Settings of the RFEM manual.
For better convergence and to avoid instabilities in nonlinear structural systems, it is recommended to use several load steps. However, a large "Number of load increments" has a detrimental effect on the speed of the calculation.
Modeling
A "member length factor" specifies the length of the member equivalent model. The larger value of the length and width of the circumscribed rectangle is multiplied by the value entered here.
Mesh
The last category provides various setting options for an FE mesh, as different meshes may be required depending on the joint type. You can specify the minimum and maximum element size in "General".
Furthermore, you can adjust the number or size of the finite elements for various components, such as members, plates, bolts, or welds, to correspond to the joint geometry. The greater the number of elements or the smaller their size, the finer the meshing.
The default settings of the design parameters should be used for the most cases, as they provide sufficiently accurate results with regard to the calculation time.