FLOOD08298

• County: Statewide
• Basin: Statewide
• Title: Computer Determination of Flow Through Bridges
• Date: 2/1/1979
• Prepared For: US
• Prepared By: COE
• Floodplain - Doc Type: Educational/Technical/Reference Information

where:

.

"Pl . projected area of the piers (or obstruction, if trash is in-
cluded) normal to the direction of flow corresponding to the
flow depth Yl at Section 1.
Ypl . vertical distance from water surface to centroid of Apl'
Koch and Carstanjen suggested that the dynamic force be reduced by one-

third for piers with semi-circular ends. In general terms the dynamic

force can be expressed as

Cn "Pl (i
2" V Al gAl

where Cn is a drag coefficient equal to 2 for square pier ends and 1.33
for piers with semicircular ends. Substituting the above expressions
for static and dynamic forces in equation (2) and solving for the
2
momentum flux (i.e., sum of ~ + Iii ) at Section A,

2 . 2 [ ]
MA = ~ + AAYA '" Ail - "Pipl + ~l Al - ~ Apl

(3)

In a similar fashion. momentum theory may be applied between Sections

B and 3, which are located immediately upstre8lll and downstre8lll from

the downstream end of the piers, respectively. In this case, the force

exerted by the piers is in the downstre8lll direction and has only a
static component, which is equal to V"P3YP3' where
Ap3 '" projected area of piers normal to the direction of .flow
corresponsing to the flow depth Y3 at Section 3.
YP3 = vertical distance from water surface to centroid of "P3'

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