FM 5-277

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FM 5-277

CHAPTER 1

H I S T O R Y A N D U S E O F T H E B R I D G E

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At the outset of World War II, the UnitedStates (US) Army sought a versatile bridgethat could span a variety of gaps and bequickly assembled by manpower alone. Forthis reason, we adopted the design for theBritish prefabricated Bailey bridge, USnomenclature Ml. We revised the design toprovide a greater roadway width of 12% feetand designated it the Panel Bridge, BaileyM2 (Figure l-l). The British then modifiedthe US version by widening the bridge again,thus producing the extra-wide Bailey M3bridge. The US Army does not stock the M3bridge in its arsenal. The Bailey bridge is athrough-type truss bridge, the roadway beingcarried between two main girders. The trussesin each girder are formed by 10-foot panelspinned end to end. In this respect, the Baileybridge is often referred to as the “panel” or“truss” bridge.

ADVANTAGESSome of the characteristics that make theBailey bridge valuable to field commandersare—

It is easy to install. Each part of theBailey bridge is a standard machine-made piece and is interchangeable amongspans. Inmost cases, no heavy equipmentis required to assemble or launch a Baileybridge; only basic pioneer skills and equip-ment are needed.

It is highly mobile. All parts of the bridgecan be transported to and from the bridgesite by 5-ton dump trucks and trailers.

It is versatile. Standard parts can be usedto assemble seven standard truss designsfor efficient single spans up to 210 feetlong and to build panel crib piers sup-porting longer bridges. With minor non-standard modifications, the expedientuses of bridge parts are limited only bythe user’s imagination.

CONSTRUCTIONTransverse floor beams, called transoms, areclamped to the bottom chords of the trussesand support stringers and decking. Swaybraces between the girders provide horizontalbracing; rakers between the trusses andtransoms keep the trusses upright; andbracing frames and tie plates between thetrusses provide lateral bracing within eachgirder.

Main girdersThe main girders on each side of the center-line of the bridge can be assembled from asingle truss or from two or three trusses sideby side. For greater strength, a second storyof panels can be added to the trusses. Theupper stories are bolted to the top chord of thelower story. For greatest strength, a thirdstory is added. These three basic types are

shown in Figure 1-2 (page 4). The types ofpossible truss assemblies are given in Table1-1 (page 4). A single-truss, double-or triple-story bridge is never assembled because itwould be unstable. All triple-story bridgeswith the deck in the bottom story are bracedat the top by transoms and sway braceswhich are fastened to overhead-bracing sup-ports bolted to the top chords.

MaterialsThe decking, called chess, is wood. Panels,end posts, transoms, and ramps are a low-alloy, high-tensile steel. All other parts arecarbon structural steel. All joints in the partsare welded.

DeckThe clear roadway between curbs, called rib-bands, is 12 feet 6 inches wide. The transomssupporting the roadway are normally set onthe bottom chords of the bottom story. Foot-walks can be carried on the transoms outsideof the main trusses on each side of the bridge.

BearingsEnd posts pinned to the end of each truss siton cylindrical bearings which rest on a steelbase plate. On soft soil, timber grillage isused under the base” plates to distribute theload. The bridge can be assembled betweenbanks of different elevations, but the slopeshould not exceed 30 to 1.

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TYPES OF STRUCTURESPanel bridge equipment can be used toassemble fixed bridges and panel crib piersand towers. Other special structures such asfloating bridges, suspension bridges, retract-able bridges, and mobile bridges, can beassembled using special parts. Panel bridgeequipment is normally used to assemble fixedsimple-span, through-type bridges from 30 to210 feet long. The bridge can be assembled tomeet varying conditions of span and load.Bridge weight per bay is given in Table 1-2(page 5). The following special assemblies arealso possible:

Two-lane, through-type bridges; deck-typebridges; railway bridges; bridges on piers;and floating bridges can be built withpanel bridge equipment.

Panel crib piers and towers up to 70 feethigh supporting continuous spans, andup to 110 feet high supporting brokenspans, can be assembled with panel bridgeequipment and special crib-pier parts.

Many expedient structures can also bebuilt with panel bridge equipment. Theseinclude causeways, box anchors, towersfor floating bridge cables, and loadinghoppers and gantries.

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FM 5-277

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