pattern - What is a Structurally Sound Word™?

_{This is in the spirit of the What is a Word/Phrase™ series started by JLee with a special brand of Phrase™ and Word™ puzzles.}

If a word conforms to a special rule, I call it a Structurally Sound Word™.

Use the following examples below to find the rule.

And, if you want to analyze, here is a CSV version:

Structurally Sound Words™,Not Structurally Sound Words™
DENIED,ALLOWED

DETERMINED,UNDETERMINED
FEEBLEMINDED,STRONG-WILLED
FREETHINKER,FOLLOWER
IDENTIFIED,UNKNOWN
INFIELDER,PITCHER
INFINITE,BOUNDED
MILLIMETER,CENTIMETER
PRETEEN,TEENAGER
REMEMBERED,FORGOTTEN
REPENT,RELAPSE

RETIREMENT,CAREER
THIRTEENTH,FOURTEENTH
LIMITED,EXTRA

Answer

A structurally sound word is one such that

each letter has a full-height vertical component that could be "load-bearing" -- like a stud -- were it a physical thing. Letters that are full height but without a full vertical component, such as 'A', 'C', and 'X' are structurally 'unsound' since they don't have a "load-bearing" component that runs from top to bottom.
Structurally sound letters: BDEFHIKLMNPRT
Structurally unsound letters: ACGJOQSUVWXYZ