Military Bridge for Light Forces

Krauss-Maffei Wegmann

Category: Mobile Bridges | 29/11/2007 - 10:39:34

Motivation

Krauss-Maffei Wegmann has developed a portable Bridge for Light Forces, thus fulfilling a requirement of the German Armed Forces to cross gaps. The bridge is characterised by its:

  • Innovative concept
  • Easy handling
  • Low total weight
  • Innovative material
  • Modularity
  • Optimised structure with respect to cost and lifetime.

Specification

The bridge cross section, in form of a U, has a structural height of 0.8 m and a total width of 3.71 m. Determined by the kerbsides the carriageway width is 2.75 m. The modular bridge length is expandable in lengths from 4.8 m to 21.6 m (2 to 9 modules). The maximum gap that can be bridged is 20 m.

A 9-module bridge weighs approximately 4.3 tons. With exception of the couplings, the bridge is made entirely from carbon fibre composite material. Figures 1 and 2 show a 4-module bridge.

Military Truck on BridgeFig. 2: Military Bridge for Light Forces (4-module bridge)

Military load class is MLC 12 for wheeled and tracked vehicles. Exceptionally, MLC14 vehicles can cross the bridge at walking speed provided they keep to the centre of the carriageway.

The low cycle fatigue has been analysed on the basis of vehicle crossing tests. The side and carriage way girders have sustained more than 10,000 crossings without adverse effects concerning serviceability and load carrying capacity.

The technical requirements led to a modular bridge concept characterised by its fail-safe assembly due to the minimum number of differing components and positive-locking connections.

Only 3 different component types are necessary for the assembly of one module:

  • Side girders
  • Carriageway girders
  • Ramp girders.

Components of a 4 Module Bridge
Differentiation is made between the “Top Modules” at the bridge ends, enabling vehicles to drive on and off the bridge, and the “Intersection Modules” used to expand the bridge length.

The ramp girders are only used in the top modules whereas the carriageway girders find application in both top and intersection modules.

Thus a top module is constructed from: 2 side girders, 1 ramp girder, and 2 carriageway girders. Whereas the intersection module is erected from: 2 side girders and 3 carriageway girders.

The carriage way, ramp and side girders are joined using positive locking connections. The modules are connected by plug-in couplings in the upper and lower chords of the side girders.

The modular construction, which allows the bridges to be adjusted to local requirements and challenges, is one aspect of the development. Importance is also attached to quick and easy erection. The total bridge can be erected in less than 2 hours by 6 persons without heavy equipment. Not more than 25 kg must be lifted by any one person during erection and positioning of the bridge components.

Assembly and disassembly

Launching Nose
Bridge erection is based on the cantilever method. To begin assembly a launching nose is manually erected (see figure 4). The launching nose which initially rests on trestles consists of 2 longitudinal side beams (the bridge kerbsides) stiffened by wind bracing. The bridge is assembled module by module beginning with a top module joined to the launching nose.

As each module is completed, the whole assembly can be moved further out over the gap. The bridge balance is maintained by the weight of the modules on or behind the trestles until such time as the launching nose reaches the far side of the gap.

During erection the troupes can reach the opposite bank by means of a catwalk integrated into the launching nose.

For the assembly of the modules, the side girders are initially positioned vertically and then tilted outwards by 60°. The ramp and carriageway girders are placed between the side girders such that the coupling joints are aligned. Returning the side girders to the vertical position positively locks the modules together.

The bridge can be disassembled from either the near or the far bank by performing the above steps in the reverse order.

Mobility

Airlift of the Fully Assembled Bridge
The module construction, the small size of the individual components and the compact storage capability allow various transport options.

The bridge can be transported as components or fully erected.

For the transportation of the components carry frames and trailers are available.

Thus the bridge can be hauled by the MUNGO armoured personnel carrier, loaded in or slung from the CH53 transport helicopter or shipped by rail.

The fully assembled bridge can be airlifted by the CH53 Sea Stallion as shown in figure 5.