Page 356 - Civil Engineering Formulas

HIGHWAY AND ROAD FORMULAS 287

1.8

1.6
Load factor, K 1.4 At 85%

1.2
Std. density
1.0 K = 0.86

0.8

0.6
70 75 80 85 90 95
Specified soil compaction, %
Standard AASHTO T-99
FIGURE 11.11 Load factors for corrugated steel pipe are plotted
as a function of specified compaction of backfill.

than one pipe diameter, the total load TL is assumed to act on the pipe, and
TL P ; that is,
v
P v DL LL I H S (11.30)
When the height of cover is equal to, or greater than, one pipe diameter,

P v K(DL LL I) H S (11.31)
2
2
where P design pressure, kip/ft (MPa/m )
v
K load factor
2
2
DL dead load, kip/ft (MPa/m )
2
2
LL live load, kip/ft (MPa/m )
2
2
I impact, kip/ft (MPa/m )
H height of cover, ft (m)
S span or pipe diameter, ft (m)
Ring Compression
The compressive thrust C, kip/ft (MPa/m), on the conduit wall equals the radi-
2
2
al pressure P , kip/ft (MPa/m ), acting on the wall multiplied by the wall
v
radius R, ft (m); or C P R. This thrust, called ring compression, is the force
v