Note 86 — Chapter VII · RAILWAY BRIDGES AND VIADUCTS.

Joggles are small pieces of hard wood or cast-iron of rectangular cross section, placed between two beams, and fitted carefully into notches cut across them. The beams are then bolted firmly together. The object is to stop the slipping which would occur between the two surfaces if the beams were merely laid one on the other and loaded, and so to make two pieces of equal size act as one of double the depth, and therefore of four times the strength of a single piece. In 1841 Mr. Brunel made experiments to satisfy himself of the strength gained by this method; and he afterwards perfected the arrangement by ensuring an exact fit in the notches by tightening up the joggles with wrought-iron wedges.