撑 has a great colloquial use: 撑死了 (stuffed to bursting). Also: 撑伞 (open/hold an umbrella), 撑船 (pole a boat), 撑腰 (support/back someone up). Figuratively, 撑 means to endure or hold on: 撑不住了 (can't hold on anymore).
Left hand radical - the side-form of 手. Anchors 撑 as a hand action: propping up, holding open, poling a boat, supporting a friend. Same radical fronts 拿 to hold, 提 to lift, 抬 to raise, 扛 to shoulder - the family of bear-and-support verbs.
Right component 掌 (palm) - supplies the sound (zhǎng drifted to chēng, same zh-/ch- alternation as 长/常) and a bonus image: the palm holds things up. So 撑 reads as 'using a palm to prop' - phono-semantic, where the phonetic also carries real meaning.
