MGB Technical Specification
The lightweight alloy Medium Girder Bridge (MGB) set new standards for military bridging when it was introduced in 1971. WFEL has since sold more than 500 units to 38 different customers worldwide.
Continually modified, the MGB meets the evolving needs for bridging equipment. Highly transportable, rapidly deployed, adaptable and cost-effective, it is ideal for a wide range of military and emergency relief situations.
The MGB is a deck type, two girder bridge system, providing a 4 metre (13ft 2in) wide roadway. The basic building units comprise seven precision light alloy components. Two of the units require six personnel to lift. The other structural units each require four people. Deck units can be lifted by two people.
MGB single span bridges can be built as:
- Single Storey
- Double Storey
- Double Storey with Link Reinforcement (LRS)
Different bridge lengths are created by varying the number of bays used to suit the gap being crossed. Each bay is 1.83 metres (6ft) in length.
A single storey MGB bridge is constructed using top panels pinned together to form two girders and joined at each end by a bankseat beam creating a rigid framework.
In the Double Storey MGB bridge, the girders consist of top and bottom panels, with junction panels and end taper panels forming the sloping end of the bridge. In both cases, ramp, deck and kerb units complete the construction.
The MGB Link Reinforcement Set (LRS) consists of reinforcing links which are 3.66 metres (12ft) long, plus short links of 1.83 metres (6ft), which are pinned together to form chains under each girder.
The chains are suspended 2 metres (6ft 6in) beneath each bottom chord of the bridge and tensioned after building by pulling or winching the reinforcing posts into the vertical position. This creates a fully reinforced structure.
The Span Junction Set
The MGB Span Junction Set consists of span junction posts, pinned together at the top and connected at the bottom by hydraulic articulators.
The Span Junction Set gives the MGB Double Storey bridge a multi-span capability and allows bridges to be constructed over supports which are either fixed or floating. These may include any combination of existing supports, pontoons, existing or improvised piers and the MGB Portable Pier.
MGB Double Storey multi-span bridges take the form of two or three span structures rated at MLC 70(T). The two span bridge can have an overall length of up to 51.5 metres (169ft), while the three span can be 76 metres (250ft). This requires a total crew of 40 personnel — 24 for the main bridge, eight for the MGB Portable Pier and eight to install anchorages.
The versatility of the MGB system is shown by the adaptation of dry bridge components to a floating role. Floating MGBs can be constructed in single or double storey configurations.
Double storey construction allows landing bay spans up to 26.5 metres (86ft 11in) and is suitable for conditions where there is considerable rise and fall in water levels.
Single storey construction provides either floating bridges or ferries for load classes up to MLC 60(T).
Single and Double Storey Floating MGBs can be built using standard MGB superstructures, carried on MGB Pontoons with single storey hinge bays or double storey Span Junction Sets to provide articulation. The length of these bridges is limited only by the amount of equipment available.
The MGB Pontoon is fabricated from marine grade aluminum alloy.
Two pontoons are coupled back to back to create each pontoon pier. Three piers make up one landing bay raft. Powered pontoons are driven by a 75HP diesel engine with a water jet propulsion unit. Fully laden pontoons can operate in currents up to 2.5m/sec (4.85 knots).
Mach MGB and Hand Rail
MACH MGB (Mechanically Aided Construction by Hand) is a semi-mechanised bridge building system which reduces the size of construction crews from 25 to nine personnel without needing additional build time.
This is achieved by prefabricating MGB components into modules in a separate assembly area. The bridge is then constructed using a suitable crane or HIAB vehicle.
MACH MGB uses standard MGB components, supplemented by special components designed to assist mechanical handling.
The advantages of MACH MGB over other purpose-built mechanised systems include:
- Any suitably sized crane can be used
- Reduced manpower compared to standard MGB
- The bridge can still be built by hand if the crane or hydraulics are incapacitated
- MACH MGB is field proven and used worldwide
The MGB handrail is engineered to provide a significant increase in awareness of roadway width for both military and civilian drivers.
Vertical connecting posts with longitudinal hand rails create a continuous barrier along the edge of the bridge. Handrail components can be carried on an MGB pallet or unit transport.
MGB Product Application
|Single Storey||Up to 9.8 metre span at MLC 70 (T)|
|Double Storey||Up to 31.1 metre span at MLC 70 (T)|
|2 or 3 Multi-Span, Double Storey||2 span Up to 51.5 metres at MLC 70 (T)
3 span Up to 76 metres at MLC 70 (T)
|Double Storey Link Reinforced Set||Up to 49.4 metre span at MLC 60 (T)|
|Floating MGB: Single Storey||Up to MLC 70 (T)|
|MACH (Mechanically Aided Construction by Hand)||For reduced manpower|