M4T6 Floating Bridges And Rafts - UgliBoats
TC 5-21OChapter 5M4T6 Floating Bridges And RaftsThe M4T6 floating bridges and rafts consist ofa deck built of square, hollow aluminum sections (called balk) supported by pneumaticfloats. The M4T6 equipment is hand erectable,air transportable, and can provide the crossingforce commander with rafts and bridgescapable of supporting MLC 70 traffic in rivercurrents up to 8 FPS. The M4T6 was designedafter World War II, combining the best characteristics of the older M4 and Class 60 bridges.Proper military nomenclature for this set is theBridge, Floating, Aluminum, Highway Type,Desk Balk Superstructure on Pneumatic Floats.Until the advent of the ribbon equipment system in 1972, M4T6 equipment provided thestate of the art means of conducting militaryriver crossing operations.COMPONENTSThe major components of one set of M4T6are—FloatsThe pneumatic float which supports theM4T6 deck actually consists of two half-floats.Each half-float is 9 feet wide, 3 feet high, 22 feetlong, and weighs 750 pounds. These half-floatsare, in turn, made up of three tubes (calledsausages) laced together side by side. Thesetubes are divided into four inflatable chambers,each fitted with a valve. The tapered noses, orM4T6 Floating Bridge and Rafts37bow ends, are upswept 40 degrees and coveredwith laced skirts. The skirts prevent debris fromlodging between the tubes, improve thehydraulic characteristics of the float, andprotect the tubes from puncture during launching.Saddle AssemblyThe saddle assembly is placed upon thepneumatic float and bears the load of the bridgeitself. The saddle assembly for a float includeseight interior saddle panels, two outriggerpanels, and two saddle beams. Each saddlebeam actually consists of five individual beamsconnected by double pinned joints. The weights
TC 5-210and dimensions of these items are provided inthe figure.The two center beams rest on four saddlepanels. At each end of the center beam, ashorter beam, called an end beam extends tothe end of the level length of the float and restson two saddle panels. Each end beam is extended by a lighter, inclined outrigger beamwhich rests on an inclined outrigger panel. Thesaddle beams are equipped with cleats (on theend beams) for securing the towing lines andwith handles designed to receive the floatstraps. The center beam is also equipped withretainer lugs for receiving the saddle adapters.Saddle AdaptersThe two types of saddle adapters are normaland offset. Their primary purpose is to providea means to connect the deck balk superstructure to the saddle assembly, and to do this insuch a way to provide sufficient work space between the two. Two like saddle adapters areused per bay of bridge (per pneumatic float).The saddle adapters are connected to the center saddle beams using the sliding retainer lugslocated on these beams and their dimensionsare given in the figure. In addition to providingwork space between the saddle assembly andthe balk, the offset saddle adapters permitfloats to be placed closer together to allow forreinforced construction. To accomplish this, thebeams which receive the balk-connecting stiffener have been shifted off-center approximately 14 inches.Balk-Connecting StiffenerBalk-connecting stiffeners are secured to thesaddle adapters and are designed to receive theM4T6 Floating Bridges and Rafts38
TC 5-210bridge’s deck balk. The stiffener has 26 recesses, each spaced 9.25 inches apart. These recesses receive the lugs on the bottom of the deckbalk. Each piece of deck balk is secured to thestiffener with a steel pin. This pin is the sametype used to connect the stiffener to the saddleadapters.Deck BalkThe three types of aluminum deck balk used inconstruction of M4T6 bridges and rafts are normal, short, and tapered balk.Normal balkNormal balk is the primary component of thebridge’s deck. Normal deck balk is 15 feet long,9.25 inches in depth, and 8.5 inches wide. Normal balk weighs 225 pounds and is usually carried by four soldiers. Lugs on the lower side ofthe balk enable it to be pinned to the balk-connetting stiffener.Short balkShort balk is designed to fill gaps in the normalbalk pattern. These gaps occur—At the end of any five-float reinforced raftwith a 16-foot 7-inch overhang.At the end of any five-float normal raft witha 23-foot 4-inch overhang.At both ends of any 23-foot 4-inch or 38foot, 4-inch M4T6 fixed span.At one end of any 30- or 45-foot M4T6 fixedspan.Short balk are 8 feet 4 inches long and havethe same cross section as normal balk. Eachpiece of short balk weighs 122 pounds and canbe carried by two soldiers.M4T6 Floating Bridges and Rafts39
TC 5-210Tapered balkTapered deck balk are used to create a slopingapproach to the bridge deck and to fill gaps between the ends of normal balk. These gapsoccur —At the end of any normal floating bridgethat has a 21-foot 8-inch end span.At the end of a four-float reinforced raftwith a 21-foot 8-inch overhang.At both ends of any 21-foot 8-inch M4T6freed span.At one end of any 30- or 45-foot M4T6 fixedspan.Tapered deck balk are 6 feet 8 inches longand have the same cross section and fittings asnormal balk at one end. The other end istapered and ends in a hinged plate. Each pieceof tapered balk weighs about 100 pounds andcan be carried by two soldiers.Curb AdaptersSteel curb adapters are used to raise normaldeck balk 6 inches above the level of the roadway to provide curbing for a bridge or raft.These adapters are attached by pins to the balkconnecting stiffeners. Each adapter weighsabout 15 pounds.RampsFour aluminum alloy raft ramps are used ateach end of a raft to provide a slopingapproach. Raft ramps are a little over 3 feetwide and have an effective length of 3 feet. Theyweigh 235 pounds and are normally carried bythree soldiers. Each ramp is connected to theend of the raft by one horizontal pin and twovertical pins.M4T6 Floating Bridges and Rafts40
TC 5-210Abutment PlatesBearing platesAbutment bearing plates are 5 feet 9.75 incheslong, 1 foot wide, 3.75 inches high, and weigh165 pounds. This plate is fastened to the lastbalk-connecting stiffener on M4T6 bridges todistribute the load of the bridge on the shore.Cover platesAluminum alloy cover plates are used overjoints in the deck and at abutments and trestlesto protect balk handles from being damaged byvehicles crossing the bridge. Two short coverplates (1.5 feet long) and two long cover plates(5.3 feet long) are required to cover the normalwidth of the bridge deck. The short cover plateweighs 28 pounds while the long plate weighs 97pounds.M4T6 Floating Bridges and Rafts41
TC 5-210Trestle and BracingUniversal trestleThe universal trestle consists of one transom,two columns, two shoes, and two chain hoists.The top of the transom is fitted with recesses toaccept 22 pieces of balk. The transom is pinnedto each column. Each column has holes spacedevery 6 inches to accommodate the transom.Three holes in the transom are spaced 9 inchesapart to permit adjustments in transom height.These adjustments are made using chain hoists.Trestle (strut) bracingTrestle bracing gives lateral and longitudinalstability to the trestles. The following trestlebracing equipment is issued with each trestle:four strut braces, weighing 145 pounds each;eight bracing clamps, weighing 50 pounds each;two wrenches, weighing 13 pounds each; andfour holdfasts (with pickets), weighing 68pounds each.Other accessoriesOther accessories issued with the bridge include handrail posts (used on each side of theroadway), standard 100-pound kedge anchors,prefabricated holdfasts, a bicycle traveler forferrying operations, an inflatable craft repairkit, and a bridge erection set.ALLOCATION OF M4T6 EQUIPMENTCurrently, all active duty float bridge companies are equipped with ribbon float bridgeequipment rather than M4T6. Some US ArmyReserve and National Guard float bridge companies still maintain M4T6. Those companieswhich retain M4T6 are authorized five sets,providing about 700 feet of normal bridge or540 feet of reinforced bridge. All other M4T6M4T6 Floating Bridges and Rafts42
TC 5-210equipment is maintained in depot stocks. Oneset of M4T6 can be used to construct any one ofthe following:One 141-foot 8-inch normal bridgeOne 108-foot reinforced bridgeOne four-float normal raftOne five-float normal raftOne four-float reinforced and one five-floatreinforced raftOne six-float reinforced raftThree short fixed span bridgesTRANSPORTATION AND LOADING OFM4T6The M4T6 can be carried on any standardmilitary cargo truck or trailer having a ratedcapacity of 2 l/2 tons or more. Standard bridgetrucks include the older M821(diesel) andM139 (gasoline) bridge trucks as well as theM812 bridge transporter. The M812 chasis hasbeen modified to safely accommodate bridgeloads in excess of 5 tons. Components of the setmay also be airlifted using medium or heavy lifthelicopters LAW Appendix B.Normal Loading of M4T6 EquipmentOne set of M4T6 can be transported on 12bridge trucks. Of these trucks, 5 trucks are usedto carry normal bridge bay loads, 4 trucks carryoffset bridge loads, 1 truck carries the trestleload, 1 truck transports the anchorage load, and1 truck hauls the tools and rigging equipment.More specifically, each truck is normally loadedas shown in Table 12a, b, c, and d.M4T6 Floating Bridges and Rafts43
TC 5-210CONSIDERATIONS FOR TACTICALEMPLOYMENTBecause of the considerable time and numberof personnel required to construct M4T6 raftsand bridges, this equipment will probably notperform a major role in the rafting phase oreven in the early stages of the bridging phase ofa deliberate river crossing operation. The M4T6rafts may be needed in situations where insufficient ribbon assets are available to swiftly crossthe desired number of armored vehicles. Additionally, as the crossing force commandersecures the bridgehead area and prepares tomove forward, he will consider removing hisribbon bridges to deploy them with the advancing forces. These ribbon bridges must bereplaced with more permanent bridges to sustain lines of communications. The M4T6bridges, placed along MSRs, will normally servein this capacity. The major consideration indetermining the location of such a bridge is theexistence of a well-defined road network leading both to and from the bridge site. Other considerations include the availability of adequateassembly sites, sufficient water depth, as well asthe need for specialized equipment, such as aircompressors, cranes, and BEBs. A discussion ofthese requirements is provided in this chapter.GENERAL CONSTRUCTIONThe M4T6 floats (bays) maybe constructed byhand at the bridge site, or they maybe partiallypreassembled in rear areas and then completedupon arrival at the launch site. When bays arepreassembled, a crane or some comparablelifting device must be available to complete finalassembly of the float. The two types of M4T6bays are normal bays and offset bays. TheM4T6 Floating Bridges and Rafts44
TC 5-210difference between the two is determined by thetype of saddle adapters attached to the bay’ssaddle assembly. Normal and offset bays areconstructed in exactly the same manner.Assembly and Launching of Floats by Hand1. Two deflated half-floats are laid out stem tostern. These half-floats are connected bythreading a connecting bar through the flapson the bottom of each float, and buckling thecrisscross straps at the top of one half-floatto the D-rings of the other. One-inch manilarope may also be used in place of theconnector bar.2. Float rollers can be used to launch M4T6bays when the bays are constructed by handand no crane or other lifting device isavailable. Each float roller is equipped withtwo air valves (one at each end). Float rollersare placed beneath the uninflated M4T6float prior to the construction of theremainder of its substructure. The propermethod of positioning the float rollers is toplace the first float roller beneath theposition where the first interior saddle panelwill be placed. The additional float rollersare then spaced evenly beneath theremainder of the float.3. Once the rollers are in position, theretrieving lines are attached to each floatroller. One rope should be run through theend of each roller and secured to D-handledMT46 Floating Bridges and Rafts45pickets until the float is ready for launch.4. The float is then inflated, working from thestern to the bow. There are fourcompartments in each of the three tubeswhich make up each half-float. Eachcompartment should be filled to a pressureof 2 psi, using a 250 cubic feet per minute(CFM) air compressor.5. Once the floats are inflated, the saddleassembly crew can construct the remainderof the substructure. The 10 saddle panels areplaced on the top of the floats. These panelsare placed so that the handles on the panelsare in line with the tie-down straps on theoutside of the floats. Do not tie the panels
TC 5-210Assembly of floats by hand (continued)1. Position saddle panels so that handles are in line with tie-down straps.2. Place saddle beams on panels. Lock into place.3. Place bow/stern connecting bar.4. Place saddle adapters and balk-connecting stiffeners.MT46 Floating Bridges and Rafts46down until assembly of the substructure iscompleted.6. Next, the saddle beams are placed on top ofthe panels. The two center beams are placedon the four center panels. These beams arelocked into place using the spring-actuatedcatches on the panels. The four end beamsshould be attached once the center beamsare in place. One end beam is attached tothe end of each center beam using twoconnecting pins. The end beams are placedso that the tie-off cleat is located on the topof the beam. These beams are not attachedto the panels until the float is almostcompleted. The last beams connected arethe outrigger beams. These beams areconnected in the same manner as the endbeams.7. Once the saddle beams are in place, the twoconnecting bars are installed. Prior toinstalling one connecting bar to each end ofthe float, remove the guide pins from each ofthe outrigger beams. This will allow thebeam to be raised or lowered as neededwithout great difficulty. The connecting barsshould be threaded through the outriggerbeams and the holes provided in the skirt atthe bow end of the float. Pushup on the endsof the float to reinstall the guide pins. Allpanel should be attached to the saddlebeams at this time.8. The saddle adapters are added next. The twoadapters rest on the top of the center beams.Each adapter is held in place by the slidingretainer lugs on the beam. A safety pin isplaced on each retainer lug to prevent itfrom accidentally disengaging from thesaddle adapter.
TC 5-2109. The balk-connecting stiffeners are nextplaced on top of the saddle adapters. Thesestiffeners are fixed to the saddle adapters byfour stiffener pins (four pins are placed oneach stiffener). Curb adapters should bepinned into the 10th recess on both the leftand right side of the stiffener. Thesubstructure is now complete.10. Secure all panels to the float. Run the strapsattached to the outside of the float throughthe handle on the panel above it. If possible,the straps should also be run through thehandle on the saddle beam above the panel.The straps below the outrigger panels areattached to the outrigger beam. Next, foldthe strap in half and run it back through theD-ring to provide a quick release.11. Once the float is completely assembled, andtwo tag lines (ropes) are attached to thefloat, the float rollers may be inflated.Inflation should begin with the roller closestto the water and worked towards the rear ofthe float. Each roller is filled to a pressure of2 psi, using an air compressor. Members ofthe saddle assembly crew should man the taglines during float roller inflation.12. Once roller inflation is completed, the floatcan be pushed into the water, either by handor by the bridge truck. When the float is inthe water, the saddle assembly crew canretrieve the rollers and position them for thenext assembly and launch.pr
equipment is maintained in depot stocks. One set of M4T6 can be used to construct any one of the following: One 141-foot 8-inch normal bridge One 108-foot reinforced bridge One four-float normal raft One five-float normal raft One four-float reinforced and one five-float reinforced raft One
Seminar ‘Bridge Design with Eurocodes’ – JRC Ispra, 1-2 October 2012 13 Materials Concrete : Between C20 and C60 for composite bridges (C 90 for concrete bridges) Steel : up to S460 for steel and composite bridges (S 500 to S 700 in a separate part 1-12 for steel bridges)
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Several valise structural failures occurred at drogue and rope attachment points in initial drops All life rafts deployed and inflated: 28 operational kits, 3 life rafts were inverted on the surface Life raft visibility assessed as good Training kits visibility in the
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