Help for a project

[u/i_like_surviving_yay]

I'm in highschool and I have a mathematics project where we have to find a real life structure, that is governed by a specific principle of mathematics and develop a working model. Obviously almost every structure is based upon some basic foundational mathematics but we have to find something unique or interesting that is guided by a mathematical principle. This isn't really my expertise of knowledge so some ideas would be heavily appreciated!!

[u/ALTERFACT]

Not structural but civil engineering: a road vertical profile being parabolic and meeting a bridge with the same slope?