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Topic Name: Earthquake Performance of Gas and Water Supply Lifelines
Category: Earthquake Engineering
Research persons: George E. Brown, Jr. Network for Earthquake Engineering Simulation (NEES)
Location: School of Civil & Environmental Engineering
Cornell University, Ithaca, N.Y. 14853, United States
Details
A key component of the research has been testing at very large scale in the
Winter Laboratory. Large-scale experiments sponsored by NSF through MCEER and
the U.S.-Japan Urban Earthquake Disaster Mitigation Program in conjunction with
Tokyo Gas, Ltd. were successfully completed to evaluate the effects of
earthquake-induced ground rupture on welded steel pipelines with elbows. The
experimental set-up involved the largest full-scale replication of ground
deformation effects on pipelines ever performed in the laboratory. Figure 1
shows two experimental basins with a total of 60-65 metric tons of soil that
were displaced 1 m relative to each other to simulate the type of abrupt
displacement generated by liquefaction-induced lateral spread, landslides, and
surface faulting.
The tests allowed for calibration of a sophisticated soil-pipeline
interaction analytical program developed in conjunction with the experimental
work, known as the Hybrid Model. This model combines three dimensional shell
elements to evaluate the complex deformation and strain state induced by severe
ground movement at steel elbows with two-dimensional beam elements to simulate
soil-pipeline interaction along relatively large distances of pipeline connected
to the elbow (Yoshizaki, et al., 2001).
The experimental data and analytical modeling products are of direct
relevance for underground gas, water, petroleum, and electrical conduits. They
provide evidence critical for developing the next generation of analytical
models for three-dimensional assessment of pipe stress and deformation. The
resulting analytical models permit greater reliability and sophistication in the
evaluation of pipeline response to ground failure. The results are increased
public safety through improved engineering and more cost-effective deployment
and sitting strategies for utility companies.
The research has also involved laboratory tests on full-scale pipeline
specimens that were fabricated in the field by Los Angeles Department of Water
and Power (LADWP) and shipped to the Cornell Winter Laboratory. This research
has been performed through MCEER in conjunction with LADWP and contractors
specializing in the fabrication and installation of fiber reinforced polymer
composites (FRCs).
Figure 2 shows a load test in progress on a 300-mm-diameter welded slip joint
that was reinforced with FRC wrap developed by one of the participating
specialty contractors. The Winter Laboratory tests were conducted with a 2,700
kN loading device. The load vs. displacement behavior of FRC-wrapped and a
straight pipe section is nearly identical, and substantially higher than that of
an unreinforced slip joint.
As part of the research, robust analytical models have been developed that
can simulate the load-deformation behavior of straight pipe and welded slip
joint section with and without FRC wrap (Tutuncu, et al., 2002). Close agreement
between the results of finite element analysis and laboratory experiments has
been attained. In fact, the FEM models are able to duplicate the
force-displacement response of welded slip joints well into the post peak range.
Class A predications of prismatic pipe section buckling were able to identify
peak loads to within 2% of actual measured values as well as determine the exact
locations of wrinkling.
The results of full-scale tests on the welded slip joints of critical water
trunk lines have provided conclusive evidence that fiber reinforced composite (FRC)
wrapping can be used effectively to confine and strengthen welded slip joints
against seismic compressive forces. FRC technology can recover the full
compressive load capacity of welded slip joints such that pipelines behave as
straight sections without joints. This type of reinforcing not only can be used
to retrofit existing welded slip joints, but to strengthen new joints during
fabrication in the field.
Laboratory test results for 300-mm-diameter welded slip joints with and
without FRC strengthening confirm the predictions of the analytical model that
increases of over 100% in compressive load capacity can by achieved with FRC
wrap. LADWP is currently preparing specifications for FRC strengthening as a bid
item in future trunk line construction.
Fund:
NSF through MCEER and the U.S.-Japan Urban Earthquake Disaster
Mitigation Program in conjunction with Tokyo Gas
George E. Brown, Jr. Network for Earthquake Engineering
Simulation (NEES) Program of
the National Science Foundation
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