For example in yellow:
if all bars were rectangular, the entige frame would tend to skew. To prevent this, these diagonal bars are mounted.
What is the term for them?
Engineering Stack Exchange is a question and answer site for professionals and students of engineering. It only takes a minute to sign up.
Sign up to join this communityThe generic term is Bracing.
You will often find it further qualified as Cross Bracing, Diagonal Bracing or Triangular Bracing, depending on the whim of the person doing it.
Another common term, used in many trades, is bracing, such as diagonal bracing.
A term I recall from undergraduate Mechanics classes is Truss https://en.wikipedia.org/wiki/Truss