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EXCHANGE-RISK: EXPERIMENTAL & COMPUTATIONAL HYBRID ASSESSMENT OF NATURAL GAS PIPELINES EXPOSED TO SEISMIC RISK

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Historically, a number of major catastrophic earthquakes have resulted in a real loss of life and property worldwide. During the last decades, in particular, the overall exposure to seismic risk has increased not only due to the higher population density but also due to the more challenging construction methods and the multilayered connection between the various urban socioeconomic activities. Within this complex built environment, the energy transportation systems, despite their structural simplicity, are seemingly one of the weakest links in terms of seismic safety. Currently, energy production, preservation and safe transportation is one of the top priorities. This demands the need to eliminate the probability of occurrence of a potential seismically induced failure (i.e., related to explosion, fire, leakage etc) that would not only have devastating environmental impact in the affected areas, but could also cause operation disruptions with equally significant socioeconomic consequences throughout Europe. EXCHANGE-Risk is an Intersectoral/International, Research and Innovation transfer scheme between academia and the industry in Europe and North America focusing on mitigating Seismic Risk of buried steel pipeline Networks subjected to ground-imposed permanent and co-seismic deformations. This paper discusses the challenges addressed by EXCHANGE-Risk and the recent advancements made in this topic. It also paves the road for further discussion on the methodologies, experiments and tools that need to be developed to mitigate seismic risk of natural gas pipelines at a European level and beyond.
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EXCHANGE-RISK: EXPERIMENTAL & COMPUTATIONAL
HYBRID ASSESSMENT OF NATURAL GAS PIPELINES EXPOSED TO
SEISMIC RISK
Anastasios SEXTOS
1
, Stathis BOUSIAS
2
, Oh-Sung KWON
3
, Luigi DI SARNO
4
, Amir KAYNIA
5
,
George MANOLIS
6
, Adam CREWE
7
, Peter FURTNER
8
, Helmut WENZEL
9
, Iunio IERVOLINO
10
,
George BALTZOPOULOS
11
, Frank WUTTKE
12
, Carsten KOENKE
13
, Volkmar ZABEL
14
, Robert
BORSUTZKY
15
, George DEODATIS
16
ABSTRACT
Historically, a number of major catastrophic earthquakes have resulted in a real loss of life and property
world-wide. During the last decades, in particular, the overall exposure to seismic risk has increased not
only due to the higher population density but also due to the more challenging construction methods and
the multilayered connection between the various urban socio-economic activities. Within this complex
built environment, the energy transportation systems, despite their structural simplicity, are seemingly
one of the weakest links in terms of seismic safety. Currently, energy production, preservation and safe
transportation is one of the top priorities. This demands the need to eliminate the probability of
occurrence of a potential seismically induced failure (i.e., related to explosion, fire, leakage etc) that
would not only have devastating environmental impact in the affected areas, but could also cause
operation disruptions with equally significant socio-economic consequences throughout Europe.
EXCHANGE-Risk is an Intersectoral/International, Research and Innovation transfer scheme between
academia and the industry in Europe and North America focusing on mitigating Seismic Risk of buried
steel pipeline Networks subjected to ground-imposed permanent and co-seismic deformations. This
paper discusses the challenges addressed by EXCHANGE-Risk and the recent advancements made in
this topic. It also paves the road for further discussion on the methodologies, experiments and tools that
need to be developed to mitigate seismic risk of natural gas pipelines at a European level and beyond.
Keywords: Natural Gas Pipelines; Buried Infrastructure; Seismic Risk; Seismic Resilience
1
Associate Professor, Department of Civil Engineering, University of Bristol, Bristol, UK & Aristotle University
of Thessaloniki, Greece a.sextos@bristol.ac.uk
2
Professor, Department of Civil Engineering, University of Patras, Greece
3
Associate Professor, Department of Civil and Mineral Engineering, University of Toronto, Canada
4
Assistant Professor, University of Sannio, Italy & University of Liverpool, UK
5
Norwegian Geotechnical Institute, NGI, Oslo, Norway
6
Professor, Department of Civil Engineering, Aristotle University of Thessaloniki, Greece
7
Associate professor, Department of Civil Engineering, University of Bristol, Bristol, UK
8
Dr.-Ing, Vienna Consulting Engineers, Austria
9
Managing Director at WENZEL Consulting Engineers GmbH, Austria
10
Professor, Department of Civil Engineering, University of Naples, Italy
11
Dr., Department of Civil Engineering, University of Naples, Italy
12
Professor, Chair, Department of Geosciences, University of Kiel, Germany
13
Professor, Institute of Structural Mechanics, University of Weimar, Germany
14
Dr.-Ing., Institute of Structural Mechanics, University of Weimar, Germany
15
Dr.-Ing., Head of the Department for Earthquake Engineering, HOCHTIEF Engineering GmbH, Germany
16
Professor, Chair, Department of Civil Engineering and Engineering Mechanics, University of Columbia, USA
2
1. INTRODUCTION
During the last two decades, Natural Gas (NG) has become one of the essential components in the energy
supply of the 28 member-state European Union (EU), constituting one quarter of primary energy supply
and contributing significantly to electricity generation, heating, feedstock for industry and fuel for
transportation. As the European Union is currently the world’s largest importer (11 trillion cubic feet in
2012), the smooth and safe production, preservation and transportation of natural gas, is one of its top
priorities. Such is the need for undisruptive supply in natural gas, that EU has defined specific policies
for identifying threshold situations that shall trigger alert and immediate corrective actions to be taken
by both the affected Member States and the Union as a whole. As a result, the Directive 2004/67/EC of
2004, concerning measures to safeguard security of natural gas supplies, was transformed in 2010 into
the No 994/2010 Regulation (EU Official Journal, 2010) of the European Parliament to define rules,
criteria and measures that ensure undisruptive natural supply to the Union. The performance criterion
set is that in the event of a disruption of the single largest gas infrastructure, the capacity of the remaining
infrastructure, will be able to satisfy total gas demand of the calculated area during a day of exceptionally
high gas demand defined with a probability of once in 20 years. This is a high standard approach,
significantly more strict compared to the initial alert level of 2004 that set the Major Supply Disruption
(MSD) threshold level for Community response at the loss of 20% of gas imports from third countries
for at least 8 weeks (Commission of the European Communities, 2009). In the light of the above strategic
decisions, it is interesting to notice that the official EU policy is traditionally focused on measures to
satisfy the target demand to supply ratios (by keeping them higher than 1.0) solely on the basis of risk
scenarios associated with weather, geopolitical issues and human activity. This is clearly reflected on
Article 9 of the No 994/2010 Regulation where the potential risks are only identified as the “failure of
the main transmission infrastructures, storages or LNG terminals, and disruption of supplies from third
country suppliers, taking into account the history, probability, season, frequency and duration of their
occurrence as well as, where appropriate, geopolitical risks”.
2. SEISMIC RISK OF NATURAL GAS PIPELINES: A SYSTEMIC NATURAL THREAT
Notwithstanding the pragmatic approach of the EU policy on energy sufficiency it is clear that the
present approach is assessing risk on a purely geopolitical and financial basis. The reality is, however,
that pipeline networks are extensive, interconnected and interdependent constructions that are equally,
if not more, exposed to natural hazards. Given that the natural gas pipelines (and oil pipelines) are often
buried below ground or submerged to cross the sea, they might be statistically less affected by weather-
related phenomena. Nevertheless, in areas of significant seismic hazard, they are exposed to potentially
detrimental, earthquake-induced deformation demands, caused by wave propagation, active faulting
(Joshi et al., 2011; Karamitros et al., 2007), slope instability (Kaynia et al., 2014), soil liquefaction and
soil-pipeline interaction (Datta, 1999). The comparison of the present natural gas network in the
European Union with the historical earthquakes in Europe (Figure 1) reveals that the areas of
overlapping are not marginal. On the contrary, it is seen that most of the importing gates of natural gas
to the E.U. are associated to either very high (Italy, Greece, Turkey) or significant seismicity. An
additional aspect of the problem is that both offshore and onshore pipelines, despite their structural
simplicity, present high vulnerability (i.e., probability of pipeline failure for a given intensity measure
(Wijewickreme, et al., 2005)) to the aforementioned earthquake-related geohazards (Psarropoulos et
al., 2013). In fact, a moderate earthquake, which may cause only minor damage to residential buildings,
can easily lead to a local but critical failure within a pipeline network. The potential failure of pipelines
may also have a disproportional direct and indirect socio-economic impact well beyond the affected
area. As there are no political boundaries in natural disasters, consequences in one region can propagate
to affect millions of people, the cost of natural gas and the economy as a whole. Financial direct cost of
repair may also range from hundreds of thousands to millions of euros. Most importantly, a pipeline
failure (i.e., related to explosion, fire, or leakage) may have devastating environmental impact at the
vicinity of the incident. The example of the Hyogo-Ken Nanbu earthquake of 1995 in Japan is indicative:
gas leakage from buried pipelines occurred at 234 different places and generated fires at more than 531
different spots. Presently, there is a number of safety systems, including line-break detection systems
and automated valve controls designed for a “fail to close” condition, however, their operation during a
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strong earthquake, is not validated, is not guaranteed and it is in any case conditioned to the knowledge
of seismic hazard along the pipeline and the reliable estimate of the imposed deformations.
Figure 2: Historical earthquakes in Europe between 1000-2007 (left) (Giardini et al., 2013). European Natural
Gas Infrastructure (right) (Ratner et al., 2013).
3. CHALLENGES
In addressing the reliable assessment of seismic risk of natural gas pipelines, several challenges have to
be addressed from legislative, research and industrial perspectives.
3.1 Design guidelines for construction and assessment of natural gas pipelines is seismic areas
Apart from the lack of a comprehensive strategy integrating man-made and natural hazards, seismic
design of extended pipelines is also lacking a detailed legislative framework. The only design document
currently available in the E.U. is Part 4 of Eurocode 8, Chapter 6 on “Silos, tanks and pipelines”.
Different provisions apply for above-ground and buried pipelines, the main distinction being the effect
of inertia forces which is neglected in the latter case, however, there is no procedure on mitigation of
seismic risk of NG pipelines and specifically providing means for quick inspection and rehabilitation in
case of an earthquake event. Moreover, the guidelines are too general while the methodology to predict
wave-induced earthquake loading is provided in a short informative Annex based on Newmark’s method
(Newmark, 1967), thus providing an approximate, but valuable estimate of earthquake demand.
3.2 Spatially variable earthquake induced displacements along the pipeline axis
In contrast to the simplified wave propagation method prescribed in Eurocode 8, extensive research
work during the last 20 years (Burdette et al., 2008; Sextos, Kappos, & Pitilakis, 2003), that was based
on the pioneer work of other consortium partners (e.g. Deodatis, 1996; Deodatis & Shinozuka, 1989),
has shown that the dynamics of long structures under asynchronous excitation are associated with
entirely different mechanisms of response. From a physical point of view, this phenomenon can be easily
visualized by considering that, in case of an extended structure, seismic waves need a finite time to
arrive at different points of the construction, while at the same time they are continuously reflected,
refracted, and superimposed as they propagate through the soil medium. The result of this complex and
stochastic physical procedure is that seismic waves gradually lose their statistical correlation, or else,
their coherency. Local site amplifications further modify the incoming wavefield, hence , ground motion
excitation along an extended construction varies significantly in terms of its frequency content, phase
and amplitude (Der Kiureghian & Neuenhofer, 1992). Notably, these response features may be entirely
suppressed using conventional analytical methods. Most importantly, the approximate design
expressions provided by Eurocode 8 Part 2 (CEN, 2005) for addressing the problem for the case of
other extended structure (i.e., bridges) for addressing the problem are not only oversimplifying but may
4
be highly misleading (Sextos & Kappos, 2009), while they cannot easily be extrapolated for the case of
pipelines. Numerous other researchers (e.g. Lou & Zerva, 2005), however, the above findings are not
yet reflected in the present state of the European Norms. Similarly, the U.S. design codes for pipelines
do not prescribe any other means to consider the stochastic nature of earthquake input.
3.3 Soil-pipeline interaction
Part 4 of Eurocode 8 defines two distinct types of soil-pipe interaction; (a) inertial and (b) kinematic
interaction, the first being neglected given that the pipeline is embedded in the soil, while there is no
explicit guidance for the latter. Most importantly, no rules or methods are prescribed to account for soil
compliance even though since the 70’s, both small- and large-scale experiments were conducted for this
purpose. The response of pipes buried in sand under lateral (Almahakeri et al., 2014; Trautmann &
O’Rourke, 1985) and axial (El Hmadi & O’Rourke, 1988) monotonic loading was investigated with
different combinations of pipeline’s diameter (D) and embedment depth (H) thus covering a wide range
of the burial depth ratio (H/D). In some cases, oblique loadings were also examined (Guo, 2005; Nyman,
1984). These studies resulted in different, usually bi-linear, force-displacement relationships, similar to
those adopted in the U.S. (American Lifelines Alliance (ALA), 2001). In parallel to the experimental
methods, numerical methods were also developed. Common ground of these studies is the consideration
of monotonic loading and the assumption of uniform soil conditions along pipeline’s length. In reality
however, natural gas (NG) pipelines are cyclically excited and, since they extend over large areas, soil
conditions along their route are expected to be different. Pioneer studies (Hindy & Novak, 1979)
indicated important pipeline stress concentration at the boundary of two different soils. In addition,
considering only vertically propagating seismic waves, both laboratory tests (Nishio, 1989) and
numerical studies using FEM and FEM/BEM (Ando et al., 1992; Liu & O’Rourke, 1997) proved local
strains to be concentrated at points where the pipeline crosses soils with different properties or at regions
with inclined soil-rock interface. In this context, the challenge is to develop reliable cyclic force-
deformation relationships for (a) axial, (b) transverse horizontal and (c) transverse vertical springs,
taking into account the potential effect of the trench wherein the pipelines are buried.
3.4 Experimentally verified modes of failure
Damage patterns in pipelines are of different form and largely dependent on a number of features related
to the properties of the material and the joint detailing: tension cracks, compression cracks, local
buckling, beam buckling, axial pull-out, crushing of bell end, crushing of spigot joints, circumferential
failure and flexural failure; all resulting from co-seismic deformation, faulting and liquefaction. Over
the years, researchers have attempted to understand pipeline strength and nonlinear behavior, most
frequently numerically (Abolmaali & Kararam, 2013; Joshi et al., 2011; Jung & Zhang, 2011; Vazouras
et al., 2010, 2012) or analytically (Karamitros et al., 2007; Karamitros et al., 2011). Various tests were
also performed as mentioned in order to account for the static stiffness of the pile-soil system.
Researchers have further addressed, based on primarily centrifuge experiments, the influence of fault
type, the influence of angle between the pipe and fault for strike-slip faults inducing net axial tension in
the pipe and the differences in the pipe behavior for strike-slip faulting which induces net axial
compression in the pipe (Abdoun et al., 2009; Almahakeri et al., 2014; Ha et al., 2008). However still,
there has been little physical modeling and tests with the specific aim to verify the numerical modeling
approaches and assumptions. There are two major challenges involved in the experimental testing of
soil-pipeline systems: One is the compliance of the surrounding soil and the large dimensions of the
problem. This has been long addressed in other extended systems, such as bridges through the concept
of pseudo-dynamic (PSD) testing in which a part of the structure can be physically tested while the rest
(the numerical part) is numerically modeled with finite elements, using an appropriate time-integration
algorithm for the equations of motion. An extension of this approach is multi-site 'Hybrid Simulation'
initiated in the United States and Japan (Kwon et al., 2005), wherein different experimental facilities,
that are remotely located simultaneously test multiple sub-components. Recently, an intercontinental
hybrid experiment was performed for the case of an extended bridge (Bousias et al., 2017). A limitation,
however, in extending this concept to the case of soil-pipeline systems is that that the latter consists a
distributed mass system for which the pseudo-dynamic testing method is not unconditionally accurate,
5
hence similar experiments are very limited and require justification.
3.5 Fragility of natural gas pipelines
A large number of the so-called fragility curves relating the probabilistic vulnerability of specific
structural systems to seismic intensity is currently available both in Europe and the US, primarily for
buildings and bridges (Kwon & Elnashai, 2006) some additionally considering soil-structure interaction
effects, surface fault rupture (Kim & Shinozuka, 2004) and pre-earthquake strengthening (Padgett &
Desroches, 2009). There exist few probabilistic expressions for the anticipated damage of pipelines
(Lanzano et al., 2013) due to earthquake loading. Notably, they solely concern local damage (tension
cracks; local buckling; beam buckling) without due consideration of the coupling between the spatially
variable ground displacements and soil-pipeline interaction that was described previously. Moreover,
fragility expressions for the Metering/Regulating stations linking the High Pressure Natural Gas
Transmission System to the local Natural Gas Distribution Network are only empirical. Limited is also
the work on connectivity performance indicators (serviceability ratio and connectivity loss) and
analytical models to predict functionality at Network level. Therefore, analytical study of pipeline
vulnerability based on experimental results as well as interaction with the construction and operation
companies of Natural Gas Networks is highly desired.
3.6 Pre- and post-earthquake management of seismic risk towards network resilience
Seismic loss scenarios have long been developed for many European areas primarily focusing on
building damage with some applications to lifelines (Pitilakis, 2007). Pioneer work has been performed
in terms of seismic risk of transportation networks wherein methodologies, software and special tools
have been developed world-wide based on network analysis (Augusti et al., 1998; Esposito et al., 2015),
seismic hazard assessment, vulnerability assessment for each network component and estimation of the
direct and indirect earthquake loss. Due to the spatial distribution of the data available and the results
obtained, a Geographical Information System is typically implemented (Sextos et al., 2008). A key tool
in the US has been the development of HAZUS methodology (FEMA-NIBS 2003) and the associated
software, which includes a module dealing with Direct Physical Damage to Lifelines - Transportation
Systems. HAZUS provides estimates of physical damage, as well as functionality, of the different
components of the roadway network, but, unlike REDARS, it does not address interdependence of
components on overall system functionality and does not perform network analysis. In its latest version
(2004), HAZUS supports consideration of multiple hazard sources (i.e., floods, tornados, earthquakes).
Other probabilistic approaches have also been developed (Stergiou & Kiremidjian, 2008) that take into
account the impact of the risk of individual network components on the overall post-earthquake system
loss and functionality. According to HAZUS, lifelines are divided into the two major categories of
transportation and utility systems. In the HAZUS model, it is assumed that pipeline damages subjected
to earthquakes are completely independent from the pipeline size, class, and mechanical specifications.
4. CURRENT FINDINGS IN THE FRAMEWORK OF EXCHANGE-RISK RESEARCH
4.1 Main objectives
EXCHANGE-Risk is an Intersectoral and International, Research and Innovation transfer scheme
between academia and the industry in Europe and North America focusing on mitigating Seismic Risk
of buried steel pipeline Networks that are subjected to earthquake-imposed permanent deformations. It
also aims in developing a (nearly real time) Decision Support System for the Rapid Pipeline Recovery
to minimize the time required for inspection and rehabilitation in case of a major earthquake.
EXCHANGE-Risk involves hybrid experimental and numerical work of the soil-pipeline system at a
pipe, pipeline and network level integrated with innovative technologies for rapid pipe inspection aiming
to:
develop a comprehensive, probabilistic methodology and state-of-the-art research knowledge
for assessing the seismic vulnerability and mitigating the associated risk of natural gas pipelines,
inclusive of its direct and indirect (socio-economic) consequences,
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perform geographically distributed hybrid and/or sub-structured experiments of a soil-supported
pipeline, considering peaks of seismic demand along its length that occur due to the spatially
variable nature of soils and earthquake ground motions
develop software to integrate novel hardware technologies for (nearly) real-time identification
of the network components with the highest probability of post-hazard failure, their rapid
inspection and the ultimate improvement of gas network resilience,
revisit the existing legislative framework in terms of design, maintenance and rehabilitation of
NG pipelines, as well as decision-making towards mitigating the Major Supply Disruption Risk.
4.2 Key research findings
At first, detailed mapping of the emerging research needs for the research and professional community
on the analysis, assessment, design and management of natural gas pipeline networks has been
performed (Psyrras & Sextos, 2018). Progress made in all front of the EXCHANGE-Risk project are
briefly presented in the following.
4.2.1 Experimental and numerical investigation of soil-pipe interaction
In light of the geographically distributed hybrid test that is planned for year 3 of the project experimental
framework has been initiated in the Universities of Bristol, Toronto and Patras. First, an experimental
setup was constructed at the University of Bristol to study the in-plane stiffness of the soil-pipe system
(Crewe et al., 2018) confirming good agreement with respect to numerical analyses and previous
findings from the literature (Figures 2 and 3). A complementary setup has also been developed in
Toronto to consider the cyclic nature of earthquake loading (Figure 4). Currently, a new experimental
configuration is setup at the University of Bristol involving a stacked-layer shear box to test the
numerically identified modes of failure of soil-pipe systems under earthquake loading (Figure 5).
Universities of Naples and Toronto further developed a demonstration-sized low-power actuator and
wrote the necessary software for the controller. This device is able to interface with the UT-SIM hybrid
simulation platform and perform small-scale tests on simplified physical specimens of soils and
pipelines. The purpose of the device is to provide a testbed for the software implementation of the
simulation before moving into the lab and connecting the controllers to hydraulic actuators.
Furthermore, it can facilitate coordinated development of the control and network communication code
among partner institutions, since similar devices can be assembled at different locations at low cost
(Figure 6).
Figure 1: Experimental setup to study the soil-pipeline static stiffness (Crewe et al., 2018).
7
Figure 2: Numerical analysis (left) under lateral loading and indicative results in comparison to previous
research findings (Nqh vs H/D curves, bottom)
Given the computational demand associated with numerical modeling of the soil-pipeline system with
3D finite elements or coupled BEM/FEM that is required in order to compute the seismic demand on
the pipeline, several lower order spring-based models have been developed including: a preliminary
Finite Element model coupled with a Boundary element method implementation and is able to study the
effects of axial, transverse horizontal and vertical loading (Stutz & Wuttke, 2018), advanced nonlinear
mechanical models combining springs, dashpots and sliders (Markou & Kaynia, 2018; Markou &
Manolis, 2016a, 2016b; Markou et al., 2018) and a novel model based on Generalized Beam Theory
that matches successfully the linear response of the corresponding shell model (Bianco, Koenke,
Habtemariam, & Zabel, 2018). The above models will be assessed and compared before identifying the
most reliable one to be used in the framework of the experiment involving problem sub-structuring and
coupling between numerical and physically tested components of the soil-pipe system.
4.2.2 Pipeline seismic demand due to spatially variable earthquake ground motion
To account for the way in which seismic demand varies along a gas pipeline in case of uniform and non-
uniform soil profiles, both a 2D linear viscoelastic and a linear-equivalent site response models were
developed for two site scenarios to predict the anticipated range of seismic demand in terms of
longitudinal strains for input motions of various intensities and frequency content. The influence of key
problem parameters is examined and the most unfavourable ground deformation cases are identified
(Papadopoulos et al., 2017). In the second stage of analysis, the critical in-plane soil displacement field
is imposed in a quasi-static manner on a long cylindrical shell model of the pipeline through a near-field
trench-like continuum soil model, and the performance of the buried pipeline is assessed. Peak nonlinear
longitudinal strains due to strong motion can be as much as two orders of magnitude larger than their
linear counterparts as a result of the severe moduli degradation.
Figure 4: Overview of the experimental setup at the University of Toronto to study the soil-pipeline system static
stiffness and detail of the soil-pipe box to be tested (bottom).
8
As shown in Figure 7 (Psyrras et al., 2018), it is demonstrated that the seismic vibrations of certain
inhomogeneous sites can generate appreciable axial stress concentration in the critically affected
pipeline segment near the discontinuity, enough to trigger coupled buckling modes in the plastic range
(Figure 8). This behavior is found to be controlled by strong axial load-moment interaction and is not
reflected in code-prescribed limit states.
Figure 3: Preliminary design of the shear stack for testing soil-pipe interaction under dynamic loading.
Figure 6: Small size low-power actuator able to interface with the UT-SIM hybrid simulation platform and
perform small-scale experimentation on simplified physical specimens.
Figure 7: Effect of spatially varying soil conditions on ground motion and pipeline axial seismic demand
(Psyrras et al, 2017)
9
Figure 8: Sample results of pipeline buckling under axial compression for different degrees of imperfection.
4.2.3 Probabilistic assessment of pipeline failure at a component and network level
The fragility of the soil-pipe system for different damage modes of failure has been studied based on
the patterns reported in the literature (Psyrras & Sextos, 2018) and the efficiency of various seismic
Intensity Measures (IM) for the structural assessment of gas pipelines under transient ground shaking. A
new methodology has also been developed (De Risi et al., 2018) to assess the risk of a gas pipeline
infrastructure at regional level in the aftermath of a seismic event. Once earthquake characteristics, such
as magnitude and epicentre, are known, seismic intensity measures, such as peak ground acceleration
(PGA) and peak ground velocity (PGV), are estimated at the location of each pipe through a simulation-
based procedure. The potential updating from real-time data coming from accelerometric stations is
considered. These IMs are then used to study the cascading landslide and liquefaction hazards providing
a hybrid empirical-mechanical-based estimation of permanent ground displacements (PGD). With the
aid of literature damage and fragility functions, loss figures and damage maps are derived as decision-
support tools for network managers and stakeholders. Losses provide a preliminary estimation of repair
costs, while damage maps support the prioritisation of inspections in the aftermath of the event. The
particular risk methodology is a novel combination of consolidated approaches as different cross-
correlation models between PGA and PGV are included and, secondly, a new three-phase back-to-back
geotechnical approach is provided for both landslide and liquefaction, representing (i) the susceptibility,
(ii) the triggering, and (iii) the PGD estimation phases. To demonstrate the efficiency of the method, the
1976 Friuli earthquake and the high-pressure gas network of North-East Italy are assumed as test-bed
scenario for the risk methodology aimed at emphasising pros and cons of the different alternative options
investigated (Figure 9). The characteristics of strong ground motion recorded in nearby areas have also
been systematically studied (Iervolino, Baltzopoulos, Chioccarelli, & Suzuki, 2017) and will be used as
a benchmark case for analyses performed in the framework of EXCHANGE-Risk.
Figure 9: Sample results of spatial correlation of PGA with the corresponding probability to exceed Damage
State 0 in the area of Central Italy (De Risi et al., 2018).
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5. CONCLUSIONS
This paper presents the challenges associated with a reliable assessment and mitigation of seismic risk
of natural gas pipelines. It discusses the existing literature, the emerging research needs and the
objectives of the H2020 research project EXCHANGE-Risk, while presenting the progress made and
the key research findings up to the project mid-term. Some results are preliminary and aim to facilitate
the preparation of the final experimental campaign that involves geographically distributed testing
among the partners. In most case, they further contribute to the understanding of the way in which the
pipeline and the surrounding soil interact under seismic loading including complex material and
geometrical nonlinearities and large-scale site response that may trigger localized seismic demand peaks
along the pipeline. The fragility of the soil-pipe system is studied at both a component (i.e., pipe
segment) and network level and tools are developed for risk assessment and efficient management of
the network. Further research is currently performed through which hazard, fragility and exposure are
to be convoluted and informed by experimental testing and refined numerical analysis.
6. ACKNOWLEDGMENTS
This work was supported by the Horizon 2020 MSCA-RISE-2015 project No. 691213 entitled
"Experimental Computational Hybrid Assessment of Natural Gas Pipelines Exposed to Seismic Risk
(EXCHANGE-RISK)". This support is gratefully acknowledged.
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