Figure 1-46.—Completed 40' x 100' x 14' preengineered metal building.Figure 1-47.—Structural members of a preengineered metal building.Again, a lateral bracing system is used between thetrusses. The pony truss span is the same as thatdiscussed in the preceding paragragh. Because of thesmall depth of the trusses, no top lateral bracing is used.TowersTowers are framework structures designed toprovide vertical support. They may be used to supportanother structure, such as a bridge, or they may be usedto support a piece of equipment, such as a communi-cation antenna. Since the prime purpose of a tower is toprovide vertical support for a load applied at the top, thecompression members providing this support are theonly ones that require high-structural strength. The restof the structure is designed to stiffen the verticalmembers and to prevent bending under load. Primarily,the bracing members are designed to take loads intension and are based on a series of diagonals. A typicaltrestle tower used in bridge construction is shown infigure 1-45.Preengineered Metal StructuresPreengineered metal structures are commonly usedin military construction. These structures are usuallydesigned and fabricated by civilian industry to conformwith specifications set forth by the military. Rigid framebuildings, steel towers, communications antennas, andsteel tanks are some of the most commonly usedstructures, particularly at overseas advanced bases.Prerengineered structures offer an advantage in that theyare factory built and designed to be erected in theshortest amount of time possible. Each structure isshipped as a complete kit, including all the materials andinstructions needed to erect it.Of the preengineered metal structures available, theone that is perhaps most familiar to the Seabees is thepreengineered metal building (PEB) shown in figures1-46 and 1-47. Figure 1-47 shows the nomenclature ofthe various parts of the PEB. For definition of thisnomenclature, erection details, and other important1-23
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