Advance Design provides the option to define other steel sections than those already available in the libraries. These user-defined sections can also be used for section optimization in Steel Expert.
To use the automatic section optimization with user-defined sections, a single rule must be followed: all the sections defined must be grouped in families.
There are three methods to add new sections:
2. By defining the sectional characteristics Iy, Iz, Wy etc. or using the section calculator (see FAQ: How is a user-defined section designed using the calculation program?) - user sections;
3. By defining compound sections.
The particularities of the first two methods will be presented regarding section optimization since the compound sections cannot be grouped in libraries.
Open the Description of defined geometries window and select the Defined tab.
Sections will be added in the User sections library in a new family titled New sections.
First define the section's geometrical characteristics and from the drop-down list next to Library select User Sections, and then in the Family field add a new name for the section family. Confirm by clicking the Export button. A confirmation window will appear if the export is successful. The defined section is part of the New sections family.
The same steps will be followed to add all the sections available for this family.
In the current example a couple of alternative sections have been selected in case the previously defined sections are not verified.
The new added sections are in the User sections library:
Open the Description of defined geometries window and the new sections will be added from the User tab. Select the User sections library, right-click on it and from the menu select Add a new family.
A new window will appear in which the Name and the Description of the new family are entered.
Select the created family and click the Modify button. The user can add sections by completing manually all the sectional characteristics or using the section calculator.
The following sections have been defined using the Section calculator; all the sections are "I shaped".
By using the section calculator, the fields from shear area Sy and Sz, centrifugal moment of inertia Iyz, torsional moment of inertia It, warping constant Iw and the fields for the plastic sectional characteristics are empty. These must be entered manually to successfully calculate the steel verifications of Eurocode 3. Depending of the loading state of the structure all these characteristics may be needed.
The section profile is selected in the Import user cross section families from previous versions column.
Because of the particular sections a user can define, when the section calculator or the definition of the section characteristics is used, some geometrical characteristics must be defined as well.
Open the stored shapes window from the menu: Assumptions - Steel Design - Stored shapes. In this window the section geometrical characteristics will be entered: h, b, tw, tf, r, d.
For the parametric sections the geometrical characteristics are filled automatically.
After the definition of the sections to calculate, the optimization rules must be defined in the Calculation assumptions window. From the menu select Assumptions - Steel Design - Calculation assumptions.
Select the optimization mode:
- By elements: when an element is under or over sized, the steel expert proposes to replace the first and the last cross section with more suitable shapes.
- By section: the operation is applied to all the elements with the same cross sections. The elements with variable inertia are ignored.
- By template: the operation is applied to all elements defined by the same design template.
- By name: the operation is applied to all the elements with the same name.
Calculation of new cross sections: Define the work ratio limits taken into account for the cross sections optimization. You can define the work ratio of steel elements by one limit or by both (upper and lower limits):
- If the work ratio obtained on a shape exceeds the limit set by the user (by default 100%), the steel expert proposes a more resistant shape.
- If the work ratio is less than the limit set by the user (by default 50%), the steel expert proposes a weaker cross section for which the work ratio is less than the set limit.
Maximum number of iterations per cross section: The optimization is an iterative process. Each iteration represents an increment of the cross sections in order to obtain a work ratio included in the range defined by the user. In case of failure, the process stops after a fixed number of iterations.
Number of complete calculations (This feature is available only for EC3.): When the chained optimization option is enabled, this defines the iteration number for the optimization process. The process of iteration is done alternatively for the cross section and finite elements.
This option is useful when, after the optimization, the structural efforts are redistributed within the structure.