| ECONOMICS OF SUSPENSION BRIDGES | 281 |
Eye-Bar-Cable Structure
| Eye-bar cables | 17,300 lbs. @ 12 ¢ | = $2,076.00 |
| Nickel steel | 10,100 " @ 11 ¢ | = 1,111.00 |
| Plain concrete | 90 cu. yds. @ $16.00 | = 1,440.00 |
| Mass of bases | 20 " @ $35.00 | = 700.00 |
| Total | = $5,327.00 |
|
From these figures it is seen that untreated, high-grade, nickel-steel
eye-bars can compete today with wire cables for span-lengths below about
1,400 feet. If they were heat-treated, their intensities of working stress
could probably be made as high as 40,000 lbs. per square inch, corresponding to an elastic limit of 80,000 lbs. or an ultimate strength of 120,000 lbs.
The value of these eye-bars in place would be 13 cents per lb.
Heat-Treated Nickel-Steel Comparison
2000-Foot Span.
Eye-Bar-Cable Structure
|
| Eye-bar cables | 16,100 lbs. @ 13 ¢ | = $2,093.00 |
| Nickel steel | 11,900 " @ 11 ¢ | = 1,309.00 |
| Plain concrete | 87 cu. yds. @ $16.00 | = 1,392.00 |
| Mass of bases | 18 " @ $35.00 | = 630.00 |
| Total | = $5,424.00 |
|
This is considerably less than the cost previously found for a wire-cable
structure, consequently let us test for a 2,500-ft. span.
2500-Foot Span.
Wire-Cable Structure
|
| Wire cables | 10,800 lbs. @ 23 ¢ | =$2,484.00 |
| Nickel steel | 21,400 " @ 11 ¢ | = 2,354.00 |
| Plain concrete | 97 cu. yds. @ $16.00 | = 1,552.00 |
| Mass of bases | 19 " @ $35.00 | = 665.00 |
| Total | = $7,055.00 |
| Eye-bar cables | 21,000 lbs. @ 13 ¢ | = $2,730.00 |
| Nickel steel | 14,800 " @ 11 ¢ | = 1,628.00 |
| Plain concrete | 98 cu. yds. @ $16.00 | = 1,568.00 |
| Mass of bases | 20 " @ $35.00 | = 700.00 |
| Total | = $6,626.00 |
|