Numerically controlled form construction takes the business of building concrete forms to a whole new level. This technology makes it possible to construct concrete shapes with precise, complex geometry.
Cutting polystyrene foam on a hot-wire table was an easy, inexpensive forming solution for this battered, curved wall.
The steel beams in the background are the structure for one of the pavilions on the Boston Harbor project. The rib forms are in place in the foreground, cut for a precise location by a CNC router. Notice how they fit alongside the structural steel beams.
The plywood ribs are spaced 11 in. apart, supported by shores that rest on a flat, level form table underneath.
Using Rhino software for design and a CNC router to cut the ribs and the plywood skin made it possible to achieve smooth, multidirectional curving shapes.
Two layers of 1/4-in.-thick plywood were used for the form skin. The plywood has a resin finish to ensure a good release from the concrete.
Screw holes were prelocated and drilled by the CNC router to ensure good contact with the ribs underneath and to provide a pattern on the ceiling.
The photo shows the dramatic curving of the forming system, steel rails and Nelson studs above the beams, and steel rebar placement.
The concrete was placed stiff so it would stay in place. The worker on the far left vibrates the mix for good consolidation while concrete finishers strike off the entire roof by hand.
The completed concrete work inspires a “how did they do that” look. Notice the curving lines in the ceiling left by the skin panels.