Bridge

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# Bridge - PowerPoint PPT Presentation

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. â‰¤ 10 cm. Water depth d. Longitudinal section in a bridge. B. 0.75 m. S. d. b.

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## PowerPoint Slideshow about 'Bridge' - geri

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Presentation Transcript
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.

Hydraulic Design
• Hydraulic design is conducted to obtain the number of vents (n) and the span of the vent (s)
• The selection is made such that the head losses does not exceed 10 cm.
• A simple design can be achieved following the next steps:
Assume n, then calculate S as follows:
• Adjust S to a practical value (S ≤ 5.0 m)
• Calculate the velocity through the bridge

Where Q is the discharge in m3/sec, V is the velocity in m/sec and Aw is the water area.

Aw = n . S . d

Where d is the water depth.

• Head losses is calculated as follows

Where Hl is head loss (m), g is gravitational acceleration (9.81 m/sec2), C is a constant.

C = 0.72 for S ≤ 2.0 m
• C = 0.82 for S ≤ 4.0 m
• C = 0.92 for S > 4.0 m
Example:

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.

• Sol.

Assume n = 5

S = (21-3)/5 = 3.6 m

Aw = (15+21)/2 * 3 = 54 m2

v = 18/54 = 0.33 m/sec

Av= 5 * 3.6 * 3 = 54 m2