BRIDGE ANCHORAGE (Contd)
a. Required. To determine the size of the tower which must be built, it is first
necessary to calculate the required tower height. Because the purpose of the tower
is to elevate the overhead cable to a height at least 3 ft (0.9 m) above the water
level, the formula for the required tower height (in feet) is:
HR = 3 ft (0.9 m) + S BH
where HR is the required tower height in feet, S is the initial sag,
and BH is the bank height in feet.
Because the height of the bank is used in this calculation, determine the required
tower height separately for both the near shore and the far shore (if the bank
heights of both shores are not the same).
b. Actual. Once the required tower height (in feet) is calculated, the actual
height of each tower (near and far shore) can be determined. When using the Class
60 tower, it is possible to bolt the tower cap directly to the pivot unit to obtain a
tower height of 3 ft 8 1/4 in. (1.13 m). This is the minimum possible tower height.
The tower height may be increased by adding up to six of the 10 ft 10 in. (3.30 m)
tower sections. Table 8 provides a list of possible tower heights.
Distance from the tower to the waterline. Before erecting the towers, determine
exactly where on each shore to place the towers. Both towers are placed an equal
distance from the waterline. For planning purposes, determine this distance (A) in
feet, by using the formula:
A = L G
where L is the distance between towers in feet and G is the river
width in feet.
This calculation, basically, centers the two towers on the river.
NUMBER OF TOWER SECTIONS
TOWER HEIGHT (H)
Cap, base, and pivot unit
8 1/4 in.
With 1 tower section
6 1/4 in.
With 2 tower sections
4 1/4 in.
With 3 tower sections
2 1/4 in. (11.04 m)
With 4 tower sections
1/4 in. (14.34 m)
With 5 tower sections
57 ft 10 1/4 in. (17.65 m)
With 6 tower sections
8 1/4 in. (20.95 m)
Table 8. Possible Tower Heights.