Page 188 - Buried Pipe Design

162 Chapter Three

the incremental structural forces and the total structural forces from
the accumulated incremental forces.
The soil element strain information includes the soil element strains
in x and y directions and the shear strain. Element elastic moduli
including elastic modulus, Poisson’s ratio, shear modulus, and bulk
modulus are also listed for each element. In addition, the principal
strains for each element are enumerated.
Soil element stresses that are printed include the horizontal and
vertical stresses, shear stresses, and principal stresses. The angle of
orientation of the origin of planes with respect to the principal plane,
the ratio of major to minor principal stress, and stress levels are also
printed out for each element. The stress levels are defined by Eq. (3.42)
and indicate the stress condition of each element. If the stress level is
greater than 1.0, the element has undergone a local shear failure, and
the elastic parameters used were based on a stress level of 0.95. If the
stress level is between 0.0 and 1.0, the element has not undergone
either tension or shear failure, and the elasticity parameters that were
computed were based on the indicated stress level. If the stress level
is listed to be ( 1.0), the element has undergone a tension failure. The
element elasticity parameters that were used for this condition were,
as indicated in a previous section, very small to allow for the displace-
ments that would occur for a soil element in tension.
The goal was to make the program more user-friendly with respect
to easier analysis of the PIPE response. The elimination of unneces-
sary output, the preparation of results for plotting, and the structur-
ing of data files so that calculated stresses can be treated as
preexisting stresses for a subsequent analysis are program enhance-
ments that have been made. Also, computer graphics have been incor-
porated to help visualize the modeling process. Figures 3.44 through
3.47 are computer-generated displays produced by PIPE5.

Printed results. The output of an incremental finite element program
can be voluminous. Finding the desired results can be quite cumber-
some, especially in production runs where only a few variables are
needed to present the results. Additionally, the structural response is
printed in terms of nodal forces (shears, moments, and thrusts) for
each structural element. For example, the design criteria for the FRP
pipe are pipe-wall strains. The output of PIPE is such that computed
strains due to thrust and bending are easily located. Ring deflections
are also stored in terms of percent vertical and percent horizontal
deflection for the pipe. Thus, the printed output can easily be exam-
ined to evaluate the pipe response. The user may still wish to examine
the other parameters, which are still included.