How to a set up a equation when modelling a steel beam when adjusted over a certain length the thicken and size of the beam will change.

Hi,

I'm designing a steel frame construction and all the lengths and cross bars are individual parts which will bolt together. I would like to have the cross bars and legs size and thickness to change if the spread/width/length of the frame is increased.  Iv seen this done function work but would like to know how thank you

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