Before revision: Steel framed housing development upRectangular steel frame, or "perimeter frame" of the Willis building (at right) contrasted against the diagrid frame at 30 St Mary Axe (at center), in London.
After revision: Steel frame structure upRectangular steel frame, or "perimeter frame" of the Willis building (at right) contrasted against the diagrid frame at 30 St Mary Axe (at center), in London.