Revision of the Niagara Railway Arch Bridge . 90 loading or one similar to the com-posite loading proposed in this paper. The fact remains, however, that there are still some uncertaintiesas to the uniformity of the elastic limit and the ultimate strength ofmaterials, be they steel or steel alloys, as to the exact amount to beallowed for impact and vibration and as to the distribution of stressover the cross-section of the members, or stress transmission by meansof pin and riveted joints. Therefore, for the Niagara Arch revision,after determining the minimum value of the elastic limit of the s
Revision of the Niagara Railway Arch Bridge . 90 loading or one similar to the com-posite loading proposed in this paper. The fact remains, however, that there are still some uncertaintiesas to the uniformity of the elastic limit and the ultimate strength ofmaterials, be they steel or steel alloys, as to the exact amount to beallowed for impact and vibration and as to the distribution of stressover the cross-section of the members, or stress transmission by meansof pin and riveted joints. Therefore, for the Niagara Arch revision,after determining the minimum value of the elastic limit of the steelas shown by the somewhat extensive original tests thereof, it wasdecided to adopt unit stresses that are practically two-thirds of theelastic limit of 30 000 lb. per sq. in., as follows: Tension Built truss members 20 000 lb. per sq. in. Eye-bar members 22 000 Girder flanges, net 18 000 Laterals of shapes 26 000 Shearing Girder webs 15 000 Eivets and pins 15 000 BearingEivets and pins 30 000 Compression IGirder flanges 20 000 — 200 —. Fig. 14.—Toggle for Relieving Dead Load Stress inPosts of 115-Ft. Spans. REVISION OF NIAGARA RAILWAY ARCH BRIDGE 1959 Compression units for built chords and posts, were taken from dia-grams similar to Fig. 15, using in each case the curves for an elasticlimit of 30 000 lb.; while curves for nickel steel were established foruse in future extensions of the bridge, where such material might beadopted. All these curves were established by plotting the values forcolumn unit stresses as given by Mr. Lindenthal, in the specificationsfor the Hell Gate Arch, and then drawing the smooth curve whichclosely averaged them. The formula: I p = 23 000 — 100 — r represents closely one of these curves as shown in Fig. 15 and at the top25 ooo 20 ooo 15 000 o ^10 000 5000 1 sk ftTfc < ^ r &4 4* r]% , Jte <* ?^N &fa <5£ ,% \ -v V \ V ^ N ^i COMPRESSION UNIT STRESSES-HALF OPEN STEELDEDUCED FROM LINDENTHALSHELL GATE ARCH 2 3- 1 1
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Keywords: ., bookcentury1900, bookdecade1920, bookidrevisionofni, bookyear1920
