PERMFILE54508

• Permit No: C1981020A
• IBM Index Class Name: Permit File
• Doc Date: 5/13/2002
• Section_Exhibit Name: Volume 6 APPENDIX Ds TO Fs
• Media Type: D
• Archive: Yes

z/
5. Bend Loss
Energy loss due to bends in a sewer system is in addition
to the normal wall Iriction loss in conduit flow.
• hb. Kbr2gl
where KbL ~ 0J.25
~1 90
Hence, for a given diameter, the greater the helix angle,
the less the Iriction }actor. For a given helix, the greater the
diameter, the less the friction lactor.
The values in Table 4b are based on standard helical
pipe manufactured Irom a 24-in. net-width strip a1 steel.
However, the pipes tested were of a smaller diameter for
a given helix angle. FuAher research may show even
lower values when larger diameters of standard helical
pipe for a given helix angle are taken into account.
central angle of bend (degrees)
MANNING'S "n"
Accepted values for Ivtanning's"n' for CSP and structural
plate as verified through research and model testing are
given in Tables 4a and 4b.
~celliclents of Friction for Helical CSP
Tests by the St. Anthony Falls Hydraulic Laboratory of
the University of Minnesota, in 1969, have determined that
the "n" value for spiral pipe varies directly with the
diameter of the pipe. The reason }or this is that on small
diameter pipes the spiral corrugations lorm a smaller
angle with the axis of the pipe than they do on the larger
diameters. This small angle produces a spiral flow which
reduces the Iriction factor.
Coetticlents of Friction for Structural Plate
Early model studies by the U.S. Corps of Engineers,
and analyses of the same, had been the basis for Iriction
lactors of structural plate for several years.
In 1968, full-scale measurements, the first of their kind,
were made on a 1500-ft. long 14-f t. diameter structural
plate pipe line in Leke Michigan. These measurements
indicated a lower friction factor than those derived from
model studies. As a result, the recommended values dt
Manning's "n" for structural plate pipe of it}ft. diameter
end larger have been modified as shown in Table 4a. The
values for the smaller diameters remain as they were.
Table 4a
Coefficients of Friction (nl for Structural Wate
(Manning's Formula)
Corrugations Dlameten
6" x 2" 5 1t. 7 IL t0 fl. 15 ft.
Plain - unpavetl .033 .0.32 .030 .028
25% Paved .028 .027 ,026 .024
Table 4b
Coefficients of Friction (n{for Corrugated Steel Pipe (CSP)
(Manning ~ Formula!

Riveted Helical
Corrugationa 2 2/3" x 1/Y' t 1!Y' ^ 114" 2 2/3" x i/Y'
All Dlam. 6" 10" 12" 75" 18' 21" 2a' 36" 49' 60'•120'
Unpaved .024 .072 .Ot4 .012 .013 .014 . 075 .076 .Otfl .020 .02a
25% Paved .021 .015 .077 .020 .021
Fully Paved .012 .012 .012 .012 .012
Rlveted
Cwrugatlons 3" x 1' Helieat - 3" x t'
All Diam. 36" I6" 64' 60" 66" 72" 76"-144"
npaved .027 .021 .023 .023 .024 , .025 .026 .027
% Paved .023 .019 ,020 .020 .021 .022 .022 .023
Fully Paved .012 .072 .072 .012 .012 .012 .072 .072
~',

•2a