length, height, warp
竪 centers on vertical extension: length or height in an upright direction. The warp sense is a specialized textile application where vertical threads are stretched on a loom.
竪 combines 臤 (possibly a phonetic element) with 立 (stand), suggesting something that stands upright. The exact historical development is uncertain, but the modern form clearly links to verticality.
The top 臤 looks like a firm hand (臣 and 又) holding something upright, and the bottom 立 means stand. Together they show something standing tall and vertical, like a length of cloth stretched upward on a loom.
For ジュ, imagine a jeweler measuring the height of a gem: jew -> ジュ, and the gem stands upright on the scale.