Preengineered metal structures are commonly used in military construction. These structures are usually designed and fabricated by civilian industry to conform with specifications set forth by the military. Rigid frame buildings, steel towers, communications antennas, and steel tanks are some of the most commonly used structures, particularly at overseas advanced bases. Prerengineered structures offer an advantage in that they are factory built and designed to be erected in the shortest amount of time possible. Each structure is shipped as a complete kit, including all the materials and instructions needed to erect it.

Of the preengineered metal structures available, the one that is perhaps most familiar to the Seabees is the preengineered metal building (PEB) shown in figures 1-46 and 1-47. Figure 1-47 shows the nomenclature of the various parts of the PEB. For definition of this nomenclature, erection details, and other important information regarding the PEB, you should refer to the current Steelworker TRAMAN.

There are four basic connectors used in making structural steel connections. They are bolts, welds, pins, and rivets. Bolts and welds are the most common connectors used in military construction. Pins are used for connections at the ends of bracing rods and various support members that require freedom of rotation. Commercial prefabricated steel assemblies may be received in the field with riveted conectors. Types and uses of the four basic connectors are discussed in the following text.

Bolts are used more than any other type of connectors. They are easy to use and, in contrast to all other types of connectors, require little special equipment. The development of higher strength steels and improved manufacturing processes have resulted in the production of bolts that will produce strong structural steel connections.

Specifications for most bolted structural joints call for the use of high-strength steel bolts tightened to a high tension. The bolts are used in holes slightly larger than the nominal bolt size. Joints that are required to resist shear between connected parts are designated as either friction-type or bearing-type connectors. Bolted parts should fit solidly together when they are assembled and should NOT be separated by gaskets or any other type of compressible material. Holes should be a nominal diameter, not more that 1/16 inch in excess of the nominal bolt diameter. When the bolted parts are assembled, all joint surfaces should be free of scale, burrs, dirt, and other foreign material. Contact surfaces with friction-type joints must be free of oil, paint, or other coatings.

The two principal welding processes used in structural work are electric arc welding and oxy-MAPP gas welding. In the electric arc welding process, welding heat, sufficient to fuse the metal together, is developed by an electric arc formed between a suitable electrode (welding rod) and the base metal (the metal of the parts being welded). In the oxy-MAPP gas welding process, heat is obtained by burning a mixture of MAPP gas and oxygen as it is discharged from a torch designed for this purpose. While electric arc welding is normally used for metals that are 1/8 inch or larger in thickness, oxy-MAPP gas welding is usually restricted to thinner metals.

The principal types of welds and welded joints that are suitable for structural work are shown in figures 1-48 and 1-49.

On drawings, special symbols are used to show the kinds of welds to be used for welded connections. These symbols have been standardized by the American Welding Society (AWS). You should become familiar with the basic welding symbols and with the standard location of all elements of a welding symbol. The distinction between a weld symbol and a welding symbol should be noted. A weld symbol is a basic symbol used to indicate the type of weld. Basic weld symbols are shown at the top of figure 1-50. The supplementary symbols shown in the figure are used when necessary in connection with the basic weld symbols.

A welding symbol consists of the following eight elements, or as many of these elements as are required: (1) reference line, (2) arrow, (3) basic weld symbol, (4) dimensions and other data, (5) supplementary symbols, (6) finish symbols, (7) tail, and (8) specification, process, or other reference. These elements of the welding symbol have specific standard locations with respect to each other, as shown in figure 1-50. When a finish symbol is used in a welding symbol, it indicates the method of finish, not the degree of finish. For example, a C is used to indicate finish by chipping, an M indicates machining, and a G indicates grinding.

Figure 1-50.Standard symbols for welded joints.

Figure 1-51 shows the use of a welding symbol. This figure shows a steel-pipe column that is to be welded to a baseplate. The symbol identifies to the welder that the type of weld to be used is a fillet weld, that the weld is to extend completely around the pipe-to-column joint, and that the weld is to be made in-place in the field rather than in a fabrication shop.

A detailed explanation of welding symbols and their usage is contained in Symbols for Welding and Nondestructive Testing, ANSI/AWS A2.4-86. Welding terms and definitions are found in Standard Welding Terms and Definitions, ANSI/AWS A3.0-89.