Bridge. A bridge is a structure that connects two roads across a waterway. Head losses occur while water passes through the bridge between its walls. Head losses should not exceed 10 cm. ≤ 10 cm. Water depth d. Longitudinal section in a bridge. B. 0.75 m. S. d. b.
Water depth d
Longitudinal section in a bridge.
Where Q is the discharge in m3/sec, V is the velocity in m/sec and Aw is the water area.
Where d is the water depth.
Where Hl is head loss (m), g is gravitational acceleration (9.81 m/sec2), C is a constant.
Design a bridge across a waterway having a discharge of 18 m3/sec. The bottom width is 15 m and the top width is 21 m and the water depth is 3 m.
Assume n = 5
S = (21-3)/5 = 3.6 m
Aw = (15+21)/2 * 3 = 54 m2
Av= 5 * 3.6 * 3 = 54 m2
Check of Heading Up
Since Aw = Av .. Hu = 0
Hu < 0.1 m … OK