New perspectives on the damage estimation for buried pipeline systems due to seismic wave propagation Page: 4 of 10
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ON THE USE OF PGV FOR BURIED PIPELINE DAMAGE ESTIMATION
PGV has been widely used as damage indicator for buried pipelines due to its
relationship with maximum ground strain sg (compression or tension). Newmark
(1967) proposed Equation 1 to assess sg from the ratio between PGV and
propagation velocity of seismic waves (C). Equation 1 must be modified if the
direction of analysis is not parallel to the direction of wave propagation.
For body waves, since S-waves carry more energy, they are more dangerous than P-
waves for buried pipelines. If S-waves propagate parallel to the pipeline, C is the
apparent propagation velocity with respect to the ground surface. For surface waves,
the axial effect of the Rayleigh waves is more important than the significantly less
bending strains produced by Love waves. Rayleigh waves cause a retrograde elliptical
motion in the ground particles and generate axial strains in the direction of wave
propagation, which could significantly affect pipelines. C, for Rayleigh waves, is the
phase velocity Cph and is quantified by a dispersion curve. Cph is a function of the
wavelength 2 and of the frequency f (Equation 2). O'Rourke and Liu (1999)
recommend to calculate Cph for a wavelength equal to approximately four times the
separation distance in order to obtain the maximum value of sg.
Cph = - f (2)
Rigorously, transient ground strain can be estimated from displacement time histories
through Equation 3, where x is a space variable, and s(t) and D(t) are ground strain
and displacement time histories, respectively. In Equation 3, max represents the
maximum of the expression between absolute value.
sg = max s(t) = max DQ) (3)
It is evident that if ground strain is the direct responsible of damage in buried
pipelines, sg is the optimum parameter for developing pipeline fragility formulations
despite this fact, PGV, instead of sg, has been widely used as damage indicator
mainly due to the following reasons: 1) The derivation process of D(t) (Equation 3)
with respect to a space variable x implies that the seismic records, employed in the
analysis, are referenced to an absolute time scale; this is a very significant limitation
since only ground motion information from networks liked to the same time scale and
located in the place of interest (e.g. the zone covered by a pipeline system) would be
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Pineda Porras, Omar Andrey. New perspectives on the damage estimation for buried pipeline systems due to seismic wave propagation, article, January 1, 2009; [New Mexico]. (https://digital.library.unt.edu/ark:/67531/metadc929415/m1/4/: accessed April 23, 2019), University of North Texas Libraries, Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.