The triangulation in the side trusses makes them stiff, without being too heavy, and prevents hinging at the joints between segments of the arch.Wood is a weak material if subjected to bending (consider how easy it is to break a match by bending it): in this bridge design, the timbers in the side trusses are subjected to little or no bending forces: the dominant force in the timbers tangential to the arch is simple compression, in which state wood is very strong (consider how difficult it is to break a match by pressing its ends together without bending it).The design is an implementation in timber of a voussoir arch bridge, in which the individual elements are held in a state of compression by the action of gravity on the whole structure: a voussoir bridge requires strong abutments to balance the compressive forces at the springing of the arch.The bridge spans a 50-foot river using multiple shorter lengths of timber: for instance, the horizontal element which appears to span the entire river is made of six shorter timbers jointed end-to-end.

The design is a minor triumph of mid-18th century engineering, for which credit must go to James King (d.

The red-brick building seen on the right of the photograph is the riverside building (ca.В 1460), the oldest building on the river at Cambridge, containing parts of the PresidentвЂ™s Lodge. It has subsequently been repaired in 1866 and rebuilt to the same design in 1905.

The bridge was designed in 1748 by William Etheridge (1709вЂ“76), and was built in 1749 by James Essex the Younger (1722вЂ“84).

Photo mechanic vs bridge 8