BRIDGES '96

Army's 'ribbon' bridge supports peacekeeping mission in Bosnia

David Banasiak / December 28, 2000

When American troops arrived at the banks of the Sava River, which forms
the nothern border between Croatia and Bosnia, they were faced with the
first obstacle to their peacekeeping mission in Bosnia. The river's bridges
had been destroyed or damaged during the many years of fighting and could
not be used in a crossing. Unseasonably warm weather added to the problems
by melting snow and ice and flooding the river. Rain contributed to the
flood, doubling the river's width and transforming the surrounding area
into a quagmire.


Some troops were flown to Tuzia, headquarters for the U.S. forces in Bosnia,
and others were ferried across the river; however, the Sava had to be bridged
so heavy equipment could be transported and supply lines strengthened and
maintained. U.S. Army engineers overcame the challenge with the ribbon bridge.


A ribbon bridge is a modern, compact pontoon bridge. It differs from those
used during World War II by its improved versatility and ease of delivery
and deployment. Designed at the U.S. Army Mobility Equipment Research and
Development Command at Fort Belvoir, Va., from photographs and drawings
of the Soviet PMP bridge, the ribbon bridge is composed of floating sectional
bays with an integral superstructure and floating supports. The bays are
joined together to build bridges or rafts.


There are two specially designed bays which make up a ribbon bridge or raft.
The interior bay is composed of a four-pontoon folding section made up of
two roadway pontoons and two supporting bow pontoons. The roadway pontoons
are approximately 13.4 ft wide and are connected to each other and the bow
pontoons by hinges and pins. The bow pontoons provide additional flotation
support and walkways for pedestrian traffic.


The ramp bays are designed for easy access between the shore and the interior
bays and are attached to both ends of either a ribbon raft or bridge. Like
the interior bay, the ramp bay is composed of four pontoons: two roadway
and two bow pontoons. The shore ends are tapered, and a hydraulic system
located within the bay allows the ramp to be raised to accommodate bank
heights of up to 42 in. Hinged to the roadway pontoon on the shore side
are two 7 ft extension ramps which further improve loading and unloading
operations.


Each modular bay is transported by a modified U.S. Army M812 5-ton truck,
which is capable of launching and retrieving the bays. The bays can also
be transported and launched by helicopter. Helicopters were used extensively
in the bridging operation in Bosnia after the Sava flooded the access road
to the bridge site.


While in its transporting state, the pontoons are folded together like an
accordion until the entire section resembles a three dimensional trapezoid.
After launching, usually downstream of the bridging site, the bay automatically
opens and roadway and bow latches must be secured to prevent the bay from
folding up when a vehicle crosses the bridge. The bays require a minimum
of 17 in. of water to unfold. Once unfolded, the bays are secured by BEBs,
which resemble small tug boats. BEBs then maneuver the bays into position
so the bridging crew can connect the sections. Any number of bay sections
can be attached to one another, enabling this system to bridge any width
river.


BEBs also are used to anchor the completed bridge by tying them to the downstream
side of the bridge. The number of BEBs needed to anchor a bridge depends
on the river's current. A ribbon bridge can only be used in currents from
0 to 10 fps; however, at currents over 5 fps, the boat operators and bridge
crew must have experience working in stronger currents.


Almost half the size of the 4,200 ft Golden Gate Bridge, and longer than
the 1,595 ft Brooklyn Bridge the 2,034 ft Sava ribbon bridge is the longest
pontoon bridge built by the Army since World War II. Originally targeted
for a Christmas 1995 completion, the operation was delayed by pouring rain
and rising river water. At one point the flooding became so intense that
the original bridging site on the Croatian side was turned into an island.
When the island was in danger of being totally washed away, it was shored
up with $1 million worth of gravel. The river was finally spanned on New
Year's Eve and troops and vehicles were soon crossing into Bosnia.


The Army plans to build a second ribbon bridge to allow for two-way traffic
across the river. A European bridge building company also will begin inspecting
and repairing existing bridges.

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