TM 5-5420-278-24&P0003 000003 00-1DESCRIPTION AND THEORY OF OPERATIONIMPROVED RIBBON BRIDGE (IRB)RAMP BAY M16(NSN 5420-01-470-5825) (P/N 12478918);INTERIOR BAY M17(NSN 5420-01-470-5824) (P/N 12478919).Section I. EQUIPMENT DESCRIPTION AND DATAEQUIPMENT CHARACTERISTICS, CAPABILITIES, AND FEATURESThe Improved Ribbon Bridge (IRB) is a modular bridge having a roadway surface supported by afloating integral superstructure made of aluminum that functions as a ponton. A complete ribbon bridgeconsists of a ramp bay at each bank and the required number of longitudinally connected interior baysspanning between them. The IRB has a roadway width of 14 ft 9 in. (4.5 m). Adjacent to the roadway is a 4 ft (1.2 m) walkway on the outer pontons. IRB crossing weight capacities are listed in TM 5-5920-278-10.The IRB can be used for rafting operations by using one or more interior bays joined with a ramp bay ateach end. The IRB-R and IRB-I can be individually assembled longitudinally by the bridge crew, with theassistance of bridge erection boats (BEB), at a rate of one bay per minute. In addition, IRB-R and IRB-I canbe assembled with Improved Float Bridge (IFB) ramp and interior bays at a rate of one bay every twominutes or less. An IRB bay is retrievable in five minutes or less. Each bay is transported, launched, andretrieved in a folded condition on a ribbon bridge transporter.IRB Interior Bay (IRB-I). The IRB-I is a four-ponton folding module consisting of two inner pontonsand two outer pontons. Each inner ponton is divided into two watertight compartments. The IRB-I unfoldsautomatically once released and afloat. IRB-Is are connected to each other by first manually engaging fourupper couplings, followed by two lockpins on the inner pontons. The lockpins act as bearing points betweenconsecutively joined bays, thus allowing the entire bridge to hinge with the weight of a moving vehicle anduneven water conditions.IRB Ramp Bay (IRB-R). The IRB-R is a four-ponton module that functions similar to the IRB-I, butdiffers substantially in design. The ramp end of the inner pontons extends lengthwise, beyond the outerpontons, and slopes down, forming the ramp edge. The sides of the outer pontons are slightly taperedtoward the ramp end, and attaching ramp plates are provided. The IRB-R contains a manually controlledraising mechanism that is utilized when joined to an IRB-I. The angle or height of the IRB-R can beadjusted to meet various bank conditions. The IRB-R also contains two lockable, self-draining stowageboxes recessed in the outer pontons.
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