| ECONOMICS OF MOVABLE SPANS | 305 |
| Distance center to center piers | = 175 feet |
| Distance center to center of bearings of movable span | = 170 feet |
| Vertical movement of lift span. = 150-20 | = 130 feet |
| Weight of 170-ft. fixed span. | |
| Deck 900 X 175 = 158,000 lbs. | |
| Metal 4,630 X 170 = 787,000 lbs. | |
| | |
| Total 945,000 lbs. | |
| Vertical-Lift Bridge: | |
| Structural metal. | |
| Lift span 787,000 + 945,000 X 0.13 | = 910,000 lbs. |
| Tower floor-systems 2 X 1,320 X 40 | = 105,000 lbs. |
| Total span metal | 1,015,000 lbs. |
| Towers and counterweight steel 945,000 X 0.80 | = 760,000 lbs. |
| Total | 1,775,000 lbs. |
Counterweights  | = 300 cu. yds. |
| Machinery and ropes 945,000 X 0.20 | = 190,000 lbs. |
| Bascule: | |
| Structural metal: | |
| Bascule span 787,000 + 945,000 X 0.04 | = 825,000 lbs. |
| Tower floor-system and approach span 2 X 1320 X 40 | = 105,000 lbs. |
| Total span metal | = 930,000 lbs. |
| Towers, counterweight trusses, etc. 945,000 X 1.04 | = 980,000 lbs. |
| Total | = 1,910,000 lbs. |
Counterweights  | = 640 cu. yds. |
| Machinery and trunnions. 945,000 X 0.15 | = 142,000 lbs. |
|
It will be noted from the foregoing that the estimator must be able to figure independently the weights of the 170-foot fixed span, the tower floor-systems, and the approach spans. The curves of Chapter LV of "Bridge Engineering" can be used for this purpose. |