large peg, stake, post, pillar
栱 centers on a sturdy vertical wooden piece used for support or fastening: a large peg, stake, post, or pillar.
栱 combines 木 (tree/wood) with 共, which likely contributes the sound and may suggest something shared or joined, fitting a wooden peg or post used in construction.
A wooden 木 post that is shared 共 in a structure, like a large peg or pillar holding things together.
For キョウ, imagine a large wooden peg in Kyoto 京都 (きょうと) holding up an old temple gate: Kyoto -> キョウ.