. Annual report of the Board of Regents of the Smithsonian Institution. Smithsonian Institution; Smithsonian Institution. Archives; Discoveries in science. Fig. 27. There are'innumerable forms of roofs, some entirely of wood, others entirely of iron, others mixed, which take different forms, as the braces are made either to resist compression or extension, for, as we have seen in Figs. 18 and 19, we may always substitute for a tensible brace one which acts as a strut. All well designed roof trusses will, however, bear the test of an analysis, based on the principles just enunciated. One more e
. Annual report of the Board of Regents of the Smithsonian Institution. Smithsonian Institution; Smithsonian Institution. Archives; Discoveries in science. Fig. 27. There are'innumerable forms of roofs, some entirely of wood, others entirely of iron, others mixed, which take different forms, as the braces are made either to resist compression or extension, for, as we have seen in Figs. 18 and 19, we may always substitute for a tensible brace one which acts as a strut. All well designed roof trusses will, however, bear the test of an analysis, based on the principles just enunciated. One more example may be given in which this simple form of truss is extended to adapt it to the heaviest bridges with great success. The iron bridges on the Baltimore and Ohio railroad, and else- where, known as Bollman'sbridges, are made, as shown in Fig. 28, where the struts c d efg h i, and the tie rods belonging to them, sup- port the beam A B at these points. A c d e f g h. In an improvement by Fink, shown in Fig. 29,the tie rods on each side of each strut are of the same length, and therefore equally effected by changes of temperature, which is an important matter, since in Fig. 28 the struts near the ends are subjected to side strains from the unequal changes of length of the rods. This arrangement of Fink's permits, moreover, the use of much lighter tie rods for the lesser parts of the system, as indicated in the figure, and no more material is there- fore used than is absolutely necessary. Fig. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Smithsonian Institution. Board of Regents; United States National Museum. Report of the U. S. National Museum; Smithsonian Institution. Report of the Secretary. Washington : Smithsonian Institution
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