As well as helping to check a frame's compliance with the design rules, Steel Designer can also help you to select the lightest weight section that satisfies the design rules.

To design a member or group of members

Ø  Select the required members in the Frame window

Ø  Choose Design… from the Design menu

       ASD, AIJ

       AS4100, NZS3404

Ø  Check the boxes of the design rules to be used when designing

Ø  Shift-Click on the load case names in the list to include or remove them from the check

Ø  If you want a summary report in the Report window, check the Brief or Full report radio buttons

Ø  Click OK

Steel Designer will design each of the selected members; searching through the group of sections the member's original section comes from, to find the lightest section in this group that meets the design rule requirements. Once the design has finished, you can view the optimum section in the Best Section column in the Member Efficiency table in the Result window. If you want to automatically assign all of the optimum sections to their respective members, you can use the Use Best Sections command from the Design menu to do this. Because changing the sections will change the results of the analysis, you will have to re-analyse the structure after doing this. You may find it useful to wait until you have designed all of the members you wish to optimise before using the Use Best Sections command.

Once you have computed an optimum weight section for a member using the Design command, the best section will be displayed in the Design Efficiency table in the Result window. You can refer to this table to compare the optimal section with the original section. If you decide that you want to permanently replace the original section with the best section you should use the Use Best Sections command from the Design menu. If you have selected members in the front window you can choose to only update the selected members or you can update the entire frame. In any case, only members, which have been designed, will be updated.

To change sections to the optimum sections designed

Ø  Choose Use Best Sections from the Design menu

Ø  Click the radio button to change just the selected members or the entire frame

Ø  Click OK

The sections of the member’s chosen will be changed to the optimal sections. After using this command you will have to re-analyse the frame to determine the effect of your change on the structure.

The user can override the design and specify the optimal section for a member using the command from the Design menu in which case the select section dialog will be displayed.  As this command does not invalidate the results of analyses it can be used to temporarily store the next section shape to be allocated to a member.  In this way other members in the frame can be investigated before having to reanalyses the structure. 

When you use the Design command, Steel Designer will try to find the lightest weight section in a member's group, which will satisfy the design requirements. If there are a large number of sections in the group, this may take some time. If you use the options to constrain the width or depth of the optimum section, Steel Designer will automatically skip the check for any sections, which don't satisfy these criteria. This means you can speed up the optimisation greatly by specifying constraints for the size of the section. For example, if you are selecting an optimum section from the W sections in the United States Section Library which contains a large number of sections, specifying an upper and lower bound for the depth will let Steel Designer automatically skip most of the sections and quickly find one of the right size.

Checking for sway when using the Design command is not recommended. It is unlikely that Steel Designer will find an optimum size member because the amount of sway is likely due to the stiffness of other members (probably the columns in another part of the frame) rather than the member under consideration. These other members will not be changed while the current member is being checked.

The Find command from the Edit menu can be used to automatically search through the structure to find members that have design values exceeding a specified value for the current load case. You can search for actions, deflections, stresses or efficiencies.

To search for a category of members

Ø  Choose Find from the Edit menu

Ø  Click on the pop-up menu to choose the category to search for

Ø  Click on the radio buttons to set the criteria for the search

Ø  Click OK

After searching through the frame, Steel Designer will select all of the members, which meet the specified criteria.