joist, cane, club, king-post
梲 centers on a sturdy wooden support piece: a joist or king-post in construction, and by extension a cane or club as a wooden rod.
梲 combines 木 (tree/wood) with 兌, which likely contributes the sound. The character refers to a wooden beam or post.
The left side is wood 木, and the right side 兌 looks like a sturdy post with a top piece. Picture a wooden joist supporting a roof, or a strong wooden cane.
For セツ, imagine a wooden joist being set into place: set -> セツ, and the beam fits perfectly.