| ECONOMICS OF SUSPENSION BRIDGES | 273 |
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without a seriously great augmentation of labor and expense. These formulae are strictly logical in form. They were derived on a theoretical basis, the coefficients thus determined being changed a few per cent, where necessary, to agree with the computed weights for the various structures which had been worked out completely. It was, therefore, decided to compute and record quantities for shorter and longer spans in order to prepare curves giving, for all practicable span-lengths, the quantities of all materials per lineal foot of main span. |
Table 29a
Ratio of Quantities of Materials in Eye-Bar-Cable Bridges to Those In
Wire-cable Bridges
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Elastic Limits of Eye-bars |
Ratios | |||||||
| Cables | Nickel Steel | Anchorages and Pier Shafts | Pier Bases | |||||
| Single Deck | Double Deck | Single Deck | Double Deck | Single Deck | Double Deck | Single Deck | Double Deck | |
| 50,000 | 3.76 | 3.75 | 0.73 | 0.69 | 1.09 | 1.08 | 1.16 | 1.15 |
| 60,000 | 2.82 | 2.82 | 0.68 | 0.66 | 1.03 | 1.02 | 1.06 | 1.08 |
| 75,000 | 2.05 | 2.05 | 0.65 | 0.62 | 0.99 | 0.98 | 1.00 | 0.96 |
| 100,000 | 1.42 | 1.41 | 0.63 | 0.60 | 0.94 | 0.93 | 1.00 | 0.88 |
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The formulae referred to are the following: Wire Cable Bridges. Stiffening Trusses. Weight of One Chord: Effect of Live Load Reversal Neglected,
Fifty Per Cent of Reversal Stress Added to Main Stress,
Seventy Five Per Cent of Reversal Stress Added to Main Stress,
Weight of Web Members: Pratt System. Effect of Live Load Reversal Neglected,
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