Engineering and Contracting . o ^. L Cri: 36 60 i56 c 3 ?D \ \. ? X ^ •-- ? . 5 i / 7 / ? /. ; /( 5 li £ J £ c £4 £6 £6 30 3£ 34 36 Soon Lengths in Hundred FeetFig. 4. Uniform Live Loads Equivalent to Class U Briages Plus Impact. or even any individual part of it, except, per-haps, the central span; and (c) it is improb-able that any load of cars—unless they areore or coal cars—will ever be uniformly fullor loaded to the assumed limit. Figure 7 shows the curves of weights forcantilever bridges of the same type and load-ing as those used in preparing the curves inFig. 6, except that the imp
Engineering and Contracting . o ^. L Cri: 36 60 i56 c 3 ?D \ \. ? X ^ •-- ? . 5 i / 7 / ? /. ; /( 5 li £ J £ c £4 £6 £6 30 3£ 34 36 Soon Lengths in Hundred FeetFig. 4. Uniform Live Loads Equivalent to Class U Briages Plus Impact. or even any individual part of it, except, per-haps, the central span; and (c) it is improb-able that any load of cars—unless they areore or coal cars—will ever be uniformly fullor loaded to the assumed limit. Figure 7 shows the curves of weights forcantilever bridges of the same type and load-ing as those used in preparing the curves inFig. 6, except that the impact on main mem- only 25 ft. These comparisons indicate thatthere is little gain, either in economy or in-crease of practicable limit of opening, in neg-lecting the effect of impact. Figures 8 and 9 (p. 689) show the percentagesof carbon steel in structures of mixed nickeland carbon steels. The cur\-es are accurate forsimple spans up to 600 ft. and for cantileverbridges with openings up to 1,800 ft., and be-. 6 65 7 ?5 (3 (S5 9 35 /O 105 II 115 It Span Lengths in Hundred Ft Fig. 5. Total Weights of Metal Per Linear Foot of Span for Double-Track, of Carbon Steel and Alloy Steels of Various Elastic Limits. bcrs of trusses is assumed to be ?ero. Thesecurves begin at main openings of 1,200 ft. andextend to the greatest practicable limitinglengths of such openings. A comparison ofthe curves of Figs. 6 and 7 shows that by neg-lecting impact on trusses there is an averagesaving of about 700 lbs. of metal per linear footof span, for all spans and all kinds of steels. yond these limits they have been continued bydeflections. These curves were prepared fromdiagrams of weights of metal in bridges ofmixed nickel and carbon steels, and the dia-grams arc the result of careful, detailed com-putations of actual designs. The percentagesare, of course, subject to great variation, be-cause no two designers would agree exactly a 688 Engineering and Contracting V
Size: 1954px × 1279px
Photo credit: © The Reading Room / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1900, bookdecade1900, bookpublisherchicago, bookyear19
