| 52 / | HD | STATIC STRUCTURES (E.G., BUILDINGS) |
| 720.1 | DF | SHAFT (I.E., ELONGATED RIGID STRUCTURE) {15} |
| 730.1 | DF | .~ Longitudinally related striplike sections {5} |
| 731.1 | | .~.~ Structural support {2} |
| 731.2 | DF | .~.~.~> Forms hollow enclosure (e.g., box beam) {3} |
| 731.7 | DF | .~.~.~> Having angular component (e.g., having L, T, Z cross-section) {2} |