Answer:
Member stiffnesses can be modified using the member stiffness modification and the structure modification. Member Stiffness Modifications can be found in the Data navigator under "Types for Members". If necessary, you can create a list of various modifications in the corresponding dialog box. Under "Modification Type", you can modify partial stiffnesses and the weight; see Image 01.
In the next step, you can also create a structure modification using "Special Objects" in the Data navigator. Activate the "Members" option in the "Main" tab of the respective dialog box to activate the "Members" tab; see Image 02.
Then, select the corresponding member stiffness modification including the respective members in the "Members" tab; see Image 03. Of course, you can also create a new member stiffness modification directly, using the drop-down menu.
In the last step, activate the desired structural modification in the corresponding load case or combination in the "Load Cases and Combinations" dialog box; see Image 04. Again, a new structural modification can be created directly from here.
