Making a strong composite beam and arching it
Timbers joined from many pieces, bent by a screw and wedged to stay arched
Studies for building one strong beam out of many separate timbers keyed together. The assembled beams are to be bent by the force of a screw; as the joints twist they open along the top, and the gaps are then packed with strong wedges so the beam locks into a permanent arched, or cambered, shape. Several long beams are drawn in perspective to show the joints and the inserted keys.
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Beam built up from many pieces
The method joins many short timbers end-to-end and side-by-side to form one long beam strong enough to span. The perspective drawings show the interlocking joints between the pieces of the composite member.
Pre-stressing the beam into an arch
Once assembled, the beam is bent by the force of a screw until all its joints are twisted and open at the top. The opened joints are then packed with strong wedges (biette), which locks the beam so that it stays permanently arched and better resists load.
Screw and wedges as the forming tools
A screw supplies the bending force, and stout wedges fill the opened joints to fix the curvature. Together they camber the composite beam without any single timber having to be pre-curved.