Page 34 - Reliability and Maintainability of In service Pipelines

Introduction 23

coefficient depending on soil and installation type (available in design
manuals).
The pressure distribution around the pipe from the applied loads (W)and
bedding reaction shall be determined from asoil-structureanalysis or a rational
approximation. Acceptable pressure distribution diagrams from soil-structure
analysis are the Heger Pressure Distribution (Fig. 1.4A) for use with the
Standard Installations, the Olander/Modified Olander Radial Pressure
Distribution (Fig. 1.4B), or the Paris/Manual Uniform Pressure Distribution
(Fig. 1.4C).

1.5.1.2 Pipe and Flow Dead Loads
The dead load of the pipe weight shall be considered in the design based on mate-
rial density. The dead load of fluid in the pipe also shall be based on the unit
weight of the stream (ASCE 15-98, 2000).

1.5.1.3 Live Load
In designing buried pipes, it is necessary to consider the impact of live loads (sur-
charge) as well as the dead loads. Live loads become a greater consideration
when a pipe is installed with shallow cover under an unsurfaced road way, rail-
roads, and/or airport runways and taxiways. Surcharge loads are calculated using
Boussinesq’s theory (Moser and Folkman, 2008), for various vehicle wheel load-
ing patterns, representing the most severe loadings which might apply in various
locations.
Both concentrated and distributed superimposed live loads should be consid-
ered in the structural design of sewers. The following equation for determining
loads due to superimposed concentrated load, such as a truck wheel load has been
presented by ASCE No.60 (2007):
C s PF
W sc 5 ð1:13Þ
L
where
W sc 5 the live load on the sewer in kg/m of length
P 5 the concentrated load (kg)
F 5 the impact factor
C s 5 the load coefficient, a function of B c and L where H is the height of fill
2H 2H
from the top of pipe to ground surface in (m) and B c is the width of the sewer
in (m)
L 5 the effective length of sewer in (m)