Like a spider spinning its web, the Structurobot rides along the metal spikes and connects new ones building trusses and connecting them into a lightweight structure. A la Eifel tower.
They go along the existing structure and add to it, perhaps analogous to ribosomes on the DNA. So typically there
are many of these structuRobots running along the beams on the construction site doing their thing.
They could be made very small, for tiny ultralight and ultra-strong miniature structures, or very large for building buildings.