In the Ultimate Configuration dialog box , you can define the basic specifications for the ultimate limit state design that applies to the steel joint design. You can create several configurations and appropriately assign them to the connections. The specifications are respectively applied to the Submodel that is created in the background for the calculation.
The 'list' on the left shows all configurations available in the model. You can use the
you can create a new configuration based on the default values of the
General Data
standard. As an alternative, you can copy by using the button
you can create an existing configuration and then adjust the design parameters. The
deletes the configuration selected in the list.
Base
The Main tab manages important 'Design Parameters' that affect the stress-strain design checks.
General
The "Perform buckling analysis" check box controls whether ultimate limit state design checks are carried out in addition to the buckling analyses. This option is deactivated by default. Select the check box if you want to perform a buckling analysis. You can then check the parameters for the buckling analysis in the Buckling tab.
Partial Safety Factors
The partial safety factors of the material γM as well as γc and γinst affect the design. In this category, you can check the preset values and adjust them, if necessary.
Analysis
The list for the Analysis Type provides a selection option between a geometrically linear and a second-order analysis. (PΔ ).
If the calculation does not converge with the default setting of a maximum of 100 iterations, you should increase the 'Maximum number of iterations' accordingly. Find more information 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 duration of the calculation.
Design check
If necessary, you can adjust the default setting for the 'Limit Plastic Strain'. Based on EN 1993‑1‑5, the default value is 5%. The parameters 'Friction coefficient for prestressed bolts' and 'Preloading force factor' affect the design if you use high-strength bolt connections. Optionally, you can perform an 'elastic design of the free bolt shaft'.
Concrete Block
In this category, you can define the 'Friction coefficient' for the concrete block in a base point. It affects the sliding resistance between the base plate and the grout layer. The value of 0.20 recommended for cf,d in EN 1993-1-8, Clause 6.2.2 is preset.
Modelling
The 'member length factor' controls the length of the equivalent model of the member. The larger value of the length and width of the circumscribed rectangle is multiplied by the value specified here. Furthermore, you can influence the 'Number of segments' that are created for round geometries. Optionally, you can arrange the 'welds on the full length of the member plate edge'.
Net
The latter 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 the 'General'.
Furthermore, you can adjust the number or size of finite elements for various components - members, plates, bolts, welds - to the geometry of the joint. The greater the number of elements or the smaller their size, the finer the meshing.
The default settings of the design parameters should be suitable for most cases and also provide sufficiently accurate results with regard to the calculation time.
Plate buckling
The Buckling tab is displayed if you have selected the Perform buckling analysis check box in the 'Main' tab.
Stability Analysis Software
In this category, you can define the 'Analysis Type' and the number of 'Eigenvalues' for the buckling analysis.
In the list, three eigenvalue methods are available for selection.
- With the default setting of 'Eigenvalue method linear', the mode shapes are determined linearly. The properties of elements acting nonlinearly, such as tension members or supports with failure criteria, are not taken into account.
- The 'Incremental Method with Eigenvalue Analysis (Nonlinear)' option allows you to consider all nonlinearities when determining mode shapes. In the course of a load step by step increase until failure occurs, the failure criteria and nonlinear effects of members, supports, or hinges are determined. The calculation is performed iteratively, and thus requires a corresponding amount of time. With this method, only the lowest eigenvalue can be determined reliably.
- With the 'incremental method without eigenvalue analysis (non-linear)', the load is increased until failure occurs. No mode shapes are determined.
Four eigenmodes are preset as the 'Number of lowest eigenvalues'. Thus, it is usually possible to obtain a reliable information about the buckling behavior.
Structural Analysis
For the buckling analysis, you have access to the same calculation parameters as described for the general settings in the Analysis section.
Design check
The plate buckling design is considered to be fulfilled if the 'limit load factor' is 15 or more. This value is recommended in EN 1993-1-1, 5.2.1(3) for αcr in a plastic design. A critical load factor of less than 15 thus represents a stability failure. You can change the default value, if necessary.