Civil Engineering Reference
In-Depth Information
To complete the static design of flexible pipelines, the designer will need to calculate
the deflection of the pipeline. The deflection depends on the applied vertical dead load
W
as well as other factors, such as the modulus of elasticity of the pipe, pipe diameter and
thickness, modulus of soil resistance (
E
, see ASCE 1982, Table 9-10), and bedding con-
stant
K
b
. Per ASCE (1982, Table 9-11), the values of the bedding constant
K
b
vary from
0.110 (bedding angle
). The bedding angle may
vary along the trench, and thus a conservative value of 0.10 is often recommended.
0
) to about 0.083 (bedding angle
180
11.4.3 Earthquake Design
Once the weight
W
of the soil bearing on top of the pipeline is known [i.e., Eqs. (11.2),
(11.3), and (11.4)], the pseudostatic force can be calculated by using Eq. (11.1)]. As an
example, use the same data from Sec. 11.4.2 (
B
2 ft,
H
10 ft, and
t
125 lb/ft
3
), and
assume that for the design earthquake, the peak ground acceleration
a
max
0.30
g.
Using
k
v
2
3
k
h
2
3
(0.30)
0.20, the pseudostatic forces are as follows [Eq. (11.1)]:
Minimum pseudostatic force:
F
v
k
v
W
min
0.20 (2500)
500 lb per linear foot
Embankment condition:
F
v
k
v
W
0.20 (4750)
950 lb per linear foot
Trench condition:
F
v
k
v
W
0.20 (3200)
640 lb per linear foot
Jacked or driven pipeline:
F
v
k
v
W
0.20 (750)
150 lb per linear foot
For jacked or driven pipeline, use the minimum value of
F
v
500 lb per linear foot.
In summary, for the example problem of a 2-ft-diameter pipeline having 10 ft of over-
burden soil with a total unit weight of 125 lb/ft
3
, the soil loads are as follows:
Minimum
Embankment
Trench
Jacked or
design load,
condition,
condition,
driven pipeline,
Pipeline design
lb/ft
lb/ft
lb/ft
lb/ft
Static load
W
2500
4750
3200
2500
*
500
*
Pseudostatic load
F
v
500
950
640
*
Using minimum design values.
11.5 RESPONSE SPECTRUM
11.5.1 Introduction
As discussed in Sec. 4.6, a response spectrum can be used to directly assess the nature of
the earthquake ground motion on the structure. A response spectrum is basically a plot
of the maximum displacement, velocity, or acceleration versus the natural period of a
