There are many types of tippers and dump trucks and trailers. Each one should ideally have a fit-for-purpose design. And they have many names.
Heavy loads in a box body put pressure on the insides of the body depending on gravitational movement. The pressure is usually greater at the bottom than at the sides. This means that there will be maximum stress at the corners in a box shape design.
In a U-shape design, sometimes called a half-pipe design, part or all of the body is rounded in the shape of a U.
A U-shape design presents many advantages over a box shape design: