3D printing: first 3D-printed steel bridge to be built over Amsterdam canal

The video discusses a project in Amsterdam where robotic arms are used to construct a bridge over a canal. The project is set to start in September. A computer program designs the structure, and robotic arms weld metal at high temperatures, eliminating the need for scaffolding. The arms are supported by the structure they build, allowing them to 'walk' across the canal as the bridge is constructed.

In what way does this technique eliminate the need for scaffolding?

Describe how the robotic arms interact with the structure they are printing.