Pin-jointed (pin-connected) truss girder bridges were very widely used in North America, but found little application in Europe (except in the case of transportable military bridges).

Pin-jointed truss girders had the distinct advantage that the components could be accurately machined in factory conditions and rapidly assembled on site. In addition, the in-plane forces in the individual structural members were uniaxial and could be accurately calculated. This allowed for economical design without adding structural redundancy, but with the possibility that failure of a single member could be critical.

However, problems could arise if the close-fitting pins seized due to corrosion or lack of lubrication, in which case the members could be subjected to unexpected bending stresses. Another potential problem was loosening of the pin joints, due to fretting - with the risk of fatigue crack initiation - or due to simple wear of the pins or the holes, leading to uncertainty about the actual stresses in the members.

See here for an interesting account of pin-connected truss bridge history, design, and problems experienced in US applications.^[1]

Designers of truss girders for installation in the British Isles favoured rigid riveted joints over pinned joints. This may have been partly influenced by significant problems which befell early UK examples. However, there was much less reluctance in constructing pin-jointed bridge trusses for use overseas.

A proportion of the British pin-jointed bridges should perhaps be described as hybrids, in the case where pinned connections were limited to the bottom chord of the girder.

Note: Bailey Bridges use pin connections, but these are used to interconnect rigid panels. Inglis Bridges also use pins, but these are part of a rigid joint system.

Sources of Information