Page 256 - Buried Pipe Design

230 Chapter Four

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Figure 4.20 FEA rerounding data for pipe buried 20 ft deep in silty-sand
soil compacted to 80 percent of Proctor density. Pipe stiffness 36
2
lb/in .

obtained from the Utah State University experiments. Table 4.12 data
from these references are plotted in Fig. 4.25.
8
For the Cole and Timblin data, the rerounding coefficients were
computed by backing out the calculated pressure strain from the total
8
measured strain plotted in Fig. 4.25. For the Sears data, 19 the
rerounding coefficient was computed by using deflection data and dif-
ferential bending stress data given in Table 4.11, both giving similar
results. These coefficients are shown in Table 4.12. For the Carlstrom
7
data the rerounding coefficients were taken from his Picture-12.
Observations. Observations from the data tables and the rerounding
plots are as follows:

1. Poor and complete haunches permit about the same rerounding to
slightly more for the poor haunch type, as shown in Tables 4.10 and
4.11. Note that initial bending strain will be less for complete
haunch since it will have a more elliptical shape and a lower D fac-
f
tor for use in the bending strain equation.

t
y
b D f (4.21)
D
D
2. The maximum residual bending strains occur when the starting
deflections are highest, as shown in Tables 4.10 and 4.11.