The most common and most likely answer to this crossword clue is the 10 letter word CROSSPIECE
I've seen this crossword clue in The Times
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More clues leading to the result CROSSPIECE
Buddy explains!

The straight part
We know that "No upright member" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case no upright member = crosspiece.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does CROSSPIECE mean?
CROSSPIECE noun- A horizontal or transverse beam or similar member that extends across or perpendicular to something.
- A bar or timber connecting two knightheads or two bitts; a timber over the windlass, with pins for belaying the running rigging.