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Eleventh U.S. National Conference on Earthquake Engineering
Integrating Science, Engineering & Policy
June 25-29, 2018
Los Angeles, California
ACHIEVING RESILIENT WATER
NETWORKS – EXPERIMENTAL
PERFORMANCE EVALUATION
B. P. Wham1, B. A. Berger2, C. Pariya-Ekkasut2, T. D. O’Rourke2, H. E.
Stewart2, T. K. Bond
ABSTRACT
Recognizing the need to improve the resilience of water distribution networks, water providers are seeking
new technologies to accommodate ground deformation associated with seismically induced fault rupture,
landslides, liquefaction-induced lateral spreading and settlement, and ground movements caused by other
natural hazards, construction, mining, and regional dewatering activities. Pipeline manufacturers have
responded to the need for improved resilience with innovative products designed to respond to significant
levels of ground deformation through the use of improved materials and jointing mechanisms. Typical
pipeline design is predicated on limiting relative displacements at pipe joints, or between the pipeline and
surrounding soil. The new pipeline systems provide the capacity for large axial movements and deflections
at joints, thus allowing pipelines to change shape, while maintaining pressure and flow, in response to
complex patterns of ground displacement. To accompany new technologies and changes in design
approaches, experimental procedures are proposed that assess the performance of hazard-resilient pipeline
technologies under extreme loading conditions. Recommendations are provided based on best practices
developed from more than sixty full-scale tests performed on pipes of various material and joint
characteristics. Focus is given to the fundamental mechanics of pipeline response to externally applied
movement: axial extension/compression and bending/joint deflection. Experimental evidence confirms that
soil-pipeline interaction under large ground deformation can be decomposed into mechanical response
parallel and perpendicular to the pipeline longitudinal axis, providing an effective means of understanding
performance and developing hazard-resilient designs. Experimental methodologies, limit state assessment,
instrumentation and load apparatus design, methods for interpreting and quantifying results, and
classification of performance with respect to developing seismic design standards for water and wastewater
pipelines are highlighted.
1Research Associate, Civil, Environmental, and Architectural Engineering, University of Colorado Boulder, Boulder,
CO 80309 (email: Brad.Wham@colordo.edu)
2Geotchnical Lifelines Group, School of Civil and Environmental Engineering, Cornell University, Ithaca, NY 14850
Wham, B.P. B.A. Berger, C. Pariya-Ekkasu, T. D. O’Rourke, H. E. Stewart, T. K. Bond, C. Argyrou. Achieving
Resilient Water Networks – Experimental Performance Evaluation. Proceedings of the 11th National Conference in
Earthquake Engineering, Earthquake Engineering Research Institute, Los Angeles, CA. 2018.
Eleventh U.S. National Conference on Earthquake Engineering
Integrating Science, Engineering & Policy
June 25-29, 2018
Los Angeles, California
Achieving Resilient Water Networks – Experimental Performance
Evaluation
B. P. Wham1, B. A. Berger2, C. Pariya-Ekkasut3, T. D. O’Rourke3, H. E. Stewart3, T. K. Bond,
and C. Argyrou3
ABSTRACT
Recognizing the need to improve the resilience of water distribution networks, water providers are
seeking new technologies to accommodate ground deformation associated with seismically induced
fault rupture, landslides, liquefaction-induced lateral spreading and settlement, and ground
movements caused by other natural hazards, construction, mining, and regional dewatering
activities. Pipeline manufacturers have responded to the need for improved resilience with
innovative products designed to respond to significant levels of ground deformation through the use
of improved materials and jointing mechanisms. Typical pipeline design is predicated on limiting
relative displacements at pipe joints, or between the pipeline and surrounding soil. The new pipeline
systems provide the capacity for large axial movements and deflections at joints, thus allowing
pipelines to change shape, while maintaining pressure and flow, in response to complex patterns of
ground displacement. To accompany new technologies and changes in design approaches,
experimental procedures are proposed that assess the performance of hazard-resilient pipeline
technologies under extreme loading conditions. Recommendations are provided based on best
practices developed from more than sixty full-scale tests, performed on pipes of various material
and joint characteristics, to evaluate the large deformation capacity of these hazard-resistant
systems. Focus is given to the fundamental mechanics of pipeline response to externally applied
movement: axial extension/compression and bending/joint deflection. Experimental evidence
confirms that soil-pipeline interaction under large ground deformation can be decomposed into
mechanical response parallel and perpendicular to the pipeline longitudinal axis. For water
distribution pipelines, this decomposition provides an effective means of understanding
performance and developing hazard-resilient designs. Experimental methodologies, limit state
assessment, instrumentation and load apparatus design, methods for interpreting and quantifying
results, and classification of performance with respect to developing seismic design standards for
water and wastewater pipelines are highlighted.
1Research Associate, Civil, Environmental, and Architectural Engineering, University of Colorado Boulder, Boulder,
CO 80309 (email: Brad.Wham@colordo.edu)
2Geotchnical Lifelines Group, Dept. of Civil Engineering, Cornell University, Ithaca, NY 14850
Wham, B.P. B.A. Berger, C. Pariya-Ekkasu, T. D. O’Rourke, H. E. Stewart, T. K. Bond, C. Argyrou. Achieving
Resilient Water Networks – Experimental Performance Evaluation. Proceedings of the 11th National Conference in
Earthquake Engineering, Earthquake Engineering Research Institute, Los Angeles, CA. 2018.
Introduction
Despite the well-documented vulnerabilities of critical lifelines systems to ground movements
imposed by seismic events, including fault rupture, landsliding, and soil liquefaction-induced
subsidence and lateral spreading, these systems remain susceptible to widespread damage that can
hinder immediate efforts of emergency services (i.e., firefighting, hospitals) as well as longer-term
economic and social community recovery [1-4]. Compared to other critical infrastructure systems
(e.g., buildings, bridges), relatively limited publications addressing seismic pipeline design are
available. ASCE Committee on Gas and Liquid Fuel Lifelines provides design guidelines for
essential oil and gas pipelines and includes consideration for seismic design [5]. Pipeline Research
Council International expanded on the previous document to include seismic design of natural gas
transmission systems [6].
For water networks, the first industry-based guidelines were introduced by the Japan Water Works
Association and based on the seismic design of earthquake-resistant ductile iron pipes [7]. This
document provided the basis for the adoption of ISO 16134: Earthquake- and subsidence-resistant
design for ductile iron pipelines [8]. A noteworthy contribution of that document was a
classification table for pipeline components that provides three tiers of performance levels for three
key joint parameters: expansion/contraction, slip-out resistance, and deflection angle.
The American Lifelines Alliance (2005) provides seismic design guidelines based on three
analytical methods requiring increasing degrees of analytical assessment [9]. While these
guidelines provide a thorough framework, they are optional recommendations that have
(unfortunately) not seen widespread adoption by the industry. The guidelines also fall short of
defining quantitative performance metrics for pipeline deformation capacity, which are useful to
manufactures for setting performance goals of innovative new products, and to utilities for both
choosing products based on general performance and developing a more comprehensive analytical
assessment of product capacity given specific project characteristics.
Efforts by professional institutions to address the absence of seismic design considerations in
current industry standards are ongoing [10,11]. For the case of seismic design of water and
wastewater pipelines, the American Society of Civil Engineers has formed a task committee
charged with developing a manual of practice that incorporates pipeline criticality, expected levels
of seismic loading, and quantifiable pipeline performance metrics. A parallel effort by the
American Water Works Association’s A21 Committee intents to propose a chapter for the M41
Manual providing a framework for seismic design of ductile iron pipe [12].
The intention of this paper is to provide a supplement to the developing seismic design frameworks
by providing a first step in the process of establishing experimental procedures for the evaluation
of seismic pipelines. Based on the authors’ experiences designing and implementing over 60 full-
scale tests, best practices are outlined and accompanied by considerations unique to external
loading imposed by large ground movements.
Many of the suggested procedures reported herein are based on experience testing the jointing
mechanisms of segmented pipelines. Segmented, in contrast to continuous, pipelines are defined
as a system in which the jointing mechanism provides an inconsistency in system stiffness, and
typically represents a location of weakness at which failure or leakage is likely to occur.
Notwithstanding, the joints provide the otherwise rigid system the capacity to accommodate
significant levels of movement through extension, contraction, and deflection. Despite the
inherent focus on segmented systems, many of the best practices presented are equally applicable
for large-scale testing of continuous pipeline systems.
Current Experimental Procedures
Present industry standards addressing performance of water distribution pipelines are predicated
on internal pressure tests and material strength characterization. For example, AWWA
C151/A21.51 requires ductile iron pipes to be tested to 500 psi (3.45 MPa) and for tensile coupon
specimens, cut from the wall of the pipe, to be tested periodically during manufacturing [13]. For
thermoplastic pipe, test procedures based on internal pressure and vacuum are available to qualify
joint performance [14] and elevated levels of internal pressure are used to quantify pipe
Hydrostatic Design Basis [15]. While valuable for regular operation, the available testing
procedures are not suitable for evaluation or quantification of a pipeline’s response to earthquake-
induced ground movement that exerts exterior loading to the pipe structure. For instance, testing
has demonstrated that joint axial tensile capacity for 6-in. (150-mm)-diameter pipe under typical
operating pressures can be several times less than the apparent axial capacity achieved during burst
testing.
To evaluate seismic performance of recently introduced hazard-resilient pipeline produces
researchers at Cornell University’s Geotechnical Lifelines Large-Scale Test Facility have
developed testing procedures that focus on the fundamental mechanics of pipeline response to
externally applied movement: axial extension/compression and bending/joint deflection.
Experimental evidence has demonstrated that soil-pipeline interaction under large ground
deformation can be decomposed into mechanical response parallel and perpendicular to the
pipeline longitudinal axis. For water distribution pipelines, this decomposition provides an
effective means of understanding performance and developing hazard-resilient designs.
General Seismic Evaluation Considerations
Several general suggestions are provided that are relevant to seismic assessment of pipeline
systems. These guidelines are applicable to both axial load tests and four-point bending tests as
well as other testing procedures to determine capability of a system to accommodate extreme
external loading conditions.
A definitive testing program for product qualification is not specifically outlined because such a
program is likely to vary depending on the system’s application. However, best practices on which
a testing program could be based are provided. For instance, it is suggested that a statistically
relevant number of tests are performed. One test is much better than none, but three or greater is
highly suggested to understand repeatability and elementary characterization of experimental
uncertainty.
Material Characterization
Reliable results from well-instrumented tensile coupon specimens are necessary to design safe
testing configurations, interpret experimental data, and for developing analytical models. The full
stress-strain response in tension is fundamental, however other characterization can be useful for
a given material. For example, a high internal pressure tests of an instrumented section of pipe
barrel was used to estimate the circumferential properties of an anisotropic, oriented polyvinyl
chloride material [16].
Loading Frame and Equipment
Whenever possible, it is preferable to design the loading mechanisms (i.e., frame, loading beams,
supports, connections) to be significantly (five to ten times) stiffer than the maximum applied load.
Ensuring that each component of a loading system is sufficiently stiff limits unintended
displacements of the loading components and limits elastic system rebound that can occur when
test specimens fail suddenly at elevated load levels. Structural design is essential and stiffening
elements in the loading system should be installed as necessary to guard against web local
crippling, flange local buckling, web local yielding, and web compression buckling.
Servo-controlled hydraulic actuators operated under displacement control are ideal for ensuring
consistent test conditions, constant displacement rate, and repeatability. Conducting tests under
displacement control is highly preferable to load control for several reasons, most importantly to
avoid “runaway” loading conditions which can compromise laboratory safety.
Internal Pressure
During earthquakes, or other events that can lead to ground movement, the internal pressure of the
pipeline is expected to be either at typical operating pressure, or at zero pressure due to failure at
another location along the systems. While it is possible some fluctuation in internal pressure may
result from transit ground waves or other operational procedures, it is impractical to assume water
pressure will be supplied continuously at levels several times the lines maximum operating
pressure.
It is the opinion of the authors that seismic testing should consider three internal pressure levels.
Most importantly, tests should be carried out at typical operating pressures, as this is the most
likely condition of the pipeline during an earthquake. Negligible internal pressure is also an
important state, and has been shown in one test to reduce axial tensile capacity of a restrained joint
by about 15% [19]. For these tests it is useful to have the specimen filled with relatively low
pressure, perhaps 5% of the typical operating pressure, so that leakage of the system can be
identified. An elevated internal pressure on the order of two times the typical operating pressure
may also be considered as a test parameter.
The use of electronic pressure transducers, a pressure regulating value and, in some cases, a flow
meter are useful components of the pressurization system. For example, internal water pressure
during compression tests must be bled to achieve consistency while additional volume is necessary
for tension testing. Both increases and decreases to internal pressure during a single bending test
sequence have been observed, requiring the operator to manually open and close valves to sustain
constant pressure in the absence of a pressure regulator.
Prior to testing every effort should be made to ensure air has been removed from the interior of the
pipe for two key reasons: (1) upon pipe failure at elevated pressure, air will expand rapidly posing
greater potential safety concerns, and (2) compressed air may escape from an elastomericly sealed
joint prematurely, providing a false indication of sustained joint leakage.
Test Specimen Size
Short specimens will be influenced by end constraints used to apply loading. In general, a total
minimum specimen length of 8D is advisable for tension/compression tests. Instruments can be
impacted by local stress concentrations at loading supports or end restraints along the pipe (e.g.,
strain gages). Experience suggests that a minimum distance of 2 to 2.5D (diameter) typically is
sufficient to minimize undesirable influence on measurements. This recommendation, illustrated
in Figure 1 by strain gage planes ST±20, may vary based on D/t ratio and other test parameters.
Limit States
Seismic pipeline evaluation should make all reasonable efforts to design tests that assess the full
performance capacity range of a system. Pipe testing can typically define two key limit states:
serviceability and ultimate. The serviceability limit state for a segmented pipe is typically defined
as sustained leakage greater than a drop per second. Joint leakage is unacceptable under typical
operating conditions (service) but, during extreme events, a leaking joint still has the capacity to
convey water to critical facilities and aid in firefighting. Continuous pipelines are likely to define
serviceability limits differently, choosing to base a serviceability limit on a particular level of
localized tensile strain concentration or percent loss of cross-sectional area due to buckling.
Regardless of the parameter, thoughtful test design coupled with competent analytical models will
allow reasonable determination of these deformation states.
The ultimate limit state is defined by structural failure or fracture of the pipeline resulting in the
inability of the pipeline to sustain adequate levels of internal pressure. “Adequate” is intentionally
vague as an ultimate limit state is not specifically defined by any standards known to the authors.
Discussions with representatives from various municipalities suggest tests which reach leakage
rates exceeding 10-15 gal/min are considered unsustainable and necessitate immediate
replacement.
Instrumentation
Discrepancy between the imposed actuator displacement and the actual displacement of the test
specimen is likely regardless of system stiffness. Seating loads are common at end connections
which fix the pipe specimen to the rigid frame and actuator. The localized relative displacement
between bell and spigot sections of pipe are frequently most important to system assessment.
These discrepancies and details can be captured sufficiently if adequate instruments are used to
measure pipeline displacements at key locations along the specimen. String potentiometers,
linearly varying differential transducers (LVDTs), and encoders are typical instruments that can
be installed along the specimen to fully capture response. It is advisable to always provide
redundant measures, especially for the most critical test variables. For instance, if the data
acquisition system (DAQ) failed to record actuator displacement, supplementary measures along
the pipe should be recorded such that an approximate measure of actuator displacement could be
Figure 1. Plan view of representative compression test configurations [21].
calculated during post-test data reduction. Data interpretation errors are made when single
measurements are taken as truth and not checked against redundant records.
In addition to displacement, applied load is a critical measurement requiring redundancy. A load
cell installed in-line with the hydraulic actuator a preferred force measurement. However, these
devices could malfunction or be damaged during a test. For axial tests, a secondary measure of
load can be provided by additional load cells incorporated into the fixed end restraint (non-actuator
end of the specimen), as shown in Figure 1. Applied load can also be calculated from strain gages
adhered to the specimen.
Strain gages provide measures of localized material deformation. Each individual gage can provide
the strain in a single direction, while combinations of gages can capture bi-axial (X-Y pairs) or
multi-directional (rosettes) stress states. Specific to pipeline testing, it is advisable to include strain
gage pairs along straight section of the pipe barrel. Typical locations are halfway between the
end/loading restraints and the jointing mechanism at the center of the specimen. Locating gage
planes away from structural inconsistences provides a “clean” measure of pipe barrel strain and
can be used as a supplementary measure of load (assuming specimen material properties are well-
characterized by material testing).
Axial Tension and Compression Testing
Prior to 2012, very few studies exist considering the structural capacity of restrained joints or
couplings for water systems. Singhal performed a series of tests on several diameters of standard
DI push-on joints without joint restraining mechanisms [17]. Maragakis et al., employed a servo-
controlled actuator to apply tensile and compressive loading to several pipe materials and
diameters [18]. Although these tests were performed on relatively short sections of pipe that were
stiffened with flanges at their ends and with no internal water pressure to indicate leakage, until
recently they provided the only reasonable test data comparing the axial performance of various
joint configurations. Recent testing at Cornell has expanded significantly the available data
regarding axial tension and compression capacity of various seismically-resilient pipelines. For
the most part, these tests adhere to consistent design practices intended to evaluate the structural
system response under worst-case loading conditions.
The most significant challenge in conducting a successful axial tension or compression test is the
end restraints that transfer sufficient force from the frame to the test specimen. Several methods
have proven successful for various materials. Weld beads applied to ductile iron pipe can provide
a reactionary surface for stiff clamps [20]. Flanges welded to the end of thin wall steel pipe have
supplied adequate load for compression testing (Figure 1), and shown some success for developing
large plastic strains during tension tests [21, 22]. The use of multiple mechanical restrains in series
was successful in testing PVCO pipe to failure in tension (Figure 2) [16,19].
Four-Point Bending Tests
Four-point bending tests are designed to evaluate the joint deflection (rotation) and pipe deflection
capacity of pipelines intended to accommodate large lateral deformation. Four-point loading,
shown in Figure 3, generates a constant moment region between the inner two loading points.
While three-point loading may give the same resulting moment, it requires a known hinge point,
or rotational center, which can shift during a test. Also, loading directly through the joint in
question could prove unfavorable if local deformations nucleates from the loading point. Ground
rupture primarily oriented perpendicular to the pipe alignment will exert a pressure distribution
along the pipeline that is better represented by a constant moment region than a point load.
Test Setup
Conventionally, four-point tests are conducted with pin and roller support conditions. Fundamental
statics suggests that a dual roller system would prove unstable, which is why a pin connection is
allocated at one end. Tests conducted by the authors have shown the efficacy of a dual roller system
[23], which allows for the migration of the rotation center during the test and ensures the specimen
remains geometrically centered relative to the loading points. In complex joint systems,
determining center of rotations have proven difficult. The center of rotation is not necessarily the
first point of contact or the centerline of a jointed system, rather it is a point that is believed to be
a hinge that allows for symmetric rotations at loading points. As deflection increases and yield
occurs, the center of rotation changes due to complex contacts inside the joint. Under large
Figure 2. Plan view of representative tension test configurations [19].
Figure 3. Elevation view of typical four-point bending test [22].
deflections, the pipe has a tendency to move towards the center. Rollers allow for equal movement
thereby preserving symmetry.
The loading supports, referred to herein as saddles, serve to transfer applied force/displacement
from the loading frame to the test specimen. Saddles need to be designed in a manner such that
they are stiff enough to transfer the load without deforming but not significantly more rigid and
the test specimen such that they induce stress concentrations and local yielding of the pipe barrel.
The first design step is to determine what applied load level will yield a straight section of pipe
under four-point bending. Then, using a stress-based approach looking at contact area between the
pipe and saddle, an adequate support can be designed. When testing specimens with high d/t ratios
or with low moduli, a saddle that fully encapsulates the pipe barrel may be necessary.
Circumferentially enclosing the pipe barrel via welding or other stiff connections is not
recommended as this could induce unwanted boundary affects. Instead, the use of a saddle similar
to Figure 4, where the pipe barrel can oval slightly (see rubber inserts between pipe and steel
support) while still resisting local deformation, is recommended.
Instrumentation
Pipe deflection can be measured through a rotation in degrees or through a radius of curvature.
Rotation is calculated by assuming straight line motion between a support and a displacement
measurement at the center of rotation and by the differences in string pots placed at crown and
invert of each joint. Under large deflections, the pipe has a tendency to move in towards the center.
This can cause misalignment of vertical displacement devices and needs to be corrected throughout
the test. If a radius of curvature measurement is required, a sufficient number of displacement
devices should be placed along the length of the specimen to capture the deformed shape. Total
station survey measurements can be taken during the test to corroborate displacement data.
Conclusions
The experimental recommendations discussed address the most fundamental tests necessary the
evaluate pipeline response to longitudinal and lateral permanent ground deformations. The
essential output of these tests, relationships for force vs. displacement (axial tension/compression)
and moment vs. rotation (four-point bending/deflection), are necessary elements of seismic design
(a) Support before test
(b) Loading point during test
Figure 4. Four-point bending boundary conditions [23].
and modeling. Results from these tests are expected to provide the bases for performance level
category qualification of new and existing products in the developing design guidelines for water
and wastewater pipelines. Each component of a hazard-resilient system (including couplings,
valves, tees, etc.) can, and should, be evaluated for seismic performance following these general
recommendations and qualified for expected levels of ground movement.
With progression comes numerous limitations, a few of which we have space for. The testing
discussed is quasi-static, omitting consideration of component performance under transient ground
displacements or cyclic loading. Also omitted is combination loading (i.e., various levels of axial
tension/compression and bending imposed at various rates), which has been shown to impact
leakage threshold for DI joints [24]. Pure shear, imposed by abrupt differential movement of two
rigid masses, is a loading state that is possible at locations where pipelines connect to buildings,
manholes, or other structures (not discussed). And these are not to mention the complications
associated with soil-structure interaction of enlarged joint restraining mechanisms [25], widely
varying soil properties, vulnerability of service connections, etc. etc.
Despite the limitations and uncertainties, the presented experimental procedures provide a first
fundamental step for evaluation and a pathway for development of innovative solutions that will
improve water network resiliency.
Acknowledgments
Great appreciation is extended to countless students and researchers that have made significant
contributions over the years to the various projects on which this work is based. Thanks is also
extended to the water agencies that asked the hard questions, and to the manufacturers that
answered with research and innovation.
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