Page 187 - Buried Pipe Design

Design of Gravity Flow Pipes 161

place before any construction layers or external loading forces are ana-
lyzed. The preexisting elements may have initial stresses specified.
Preexisting strains and nodal displacements may also be input.
Structural forces may be input for any preexisting structural elements
that are in place. Preexisting stresses in the interface elements can also
be specified. The preexisting stress concept is very convenient when one
is performing a series of analyses. The use of preexisting stresses,
strains, and displacements essentially defines the stress condition for
the preexisting elements. Construction sequences, therefore, need only
be modeled once for a given mesh and soil configuration. The preexist-
ing stresses resulting from that construction simulation can be input
for the entire mesh, and the subsequent analyses can be performed by
adding only combinations of external loads to the mesh. This can save
on computer time if the user intends to analyze the mesh for different
loading schemes without repeating the construction sequences.

External loads. External loads can be input as either concentrated
loads or uniform loads. Each loading sequence must have the number
of concentrated and uniform loads to be used. Concentrated loads are
specified by denoting the node number that will receive the load and
the x and y components of the point load. Uniform loads are specified
for each element that will receive them. The two nodes of an element
with a uniform load are specified along with nodal pressures. The
magnitude of the nodal pressure is the acting uniform load.
Trapezoidal loading can then be modeled by specifying different mag-
nitudes of the uniform load at each node.

PIPE5 output. The results of the analysis of PIPE5 are stored in a data
file specified by the user. The results contain all the input information.
Element and node information, material properties, construction and
load sequencing, preexisting element information, and initial stresses
used for estimating the initial elastic parameters are listed. For each
load construction increment, the user has an option concerning the
amount of information that will be contained on the output. If the user
does not specify that the results will be printed, the output indicates
only the load or construction increment number and the nodal forces
that were used in the load vector. If the user specifies that the results
are to be printed, the output contains all the information for the nodal
load vector, nodal displacements, structural response, soil element
strains, and soil element stresses. Nodal displacements include the
total displacements for the x, y, and rotation components and the incre-
mental displacements and rotations for that particular increment.
The structural responses that are listed include the moment, shear,
and thrust for each node of each structural member. The listing contains