Configurations and Deployment
The primary components of the MGB system are rectangular "top deck" segments, and triangular bracing "bottom deck" segments. All segments are man portable.
Short/low load bridges can be constructed using just top deck components. Bracing with the additional lower deck dramatically strengthens the bridge allowing heavier loads and longer spans. Spans can reach 30 metres.
The segments have knuckle joints at each end; assembly consists of simply engaging the knuckle joints of adjacent segments then inserting a pin through a hole down the length of the knuckle. In this way as many segments as are needed are connected end to end to form a girder of the required length to span the obstruction.
Two such longitudinal girders are constructed parallel to each other to provide the bridge's strength. Deck units are then laid between these to form a 4.0 m (13 ft 2 in) wide roadway.
MGB can be built in various configurations to provide a full range of bridging capability for use both in the forward battle area and in the communications zone. Speed of erection by the fewest number of soldiers is its major characteristic. The MGB also requires very little maintenance once erected, is air transportable in either standard palletised loads or in partially assembled bridge configurations, and all US components will fit MGBs in use by allies (except for the launching nose cross girder posts)
The bridge can be supported on unprepared and uneven ground without grillages. It is constructed on one roller beam for single-story construction; two roller beams, 4.6 m apart, for double-story construction; and on three roller beams when constructing a double-story bridge over 12 bays long. The ends of the roller beams are supported on base plates and each can be adjusted in height. No leveling or other preparation of the ground is required. Single-span bridges are launched using a centrally mounted launching nose.
Read more about this topic: Medium Girder Bridge