Transcript of Bridge Seismic Isolation Study on a Full Scale Bridge Test Myrto Anagnostopoulou SEESL Structural...
- Slide 1
- Bridge Seismic Isolation Study on a Full Scale Bridge Test
Myrto Anagnostopoulou SEESL Structural and Test Engineer Ricardo
Ecker Lay Ph.D. Candidate Andre Filiatrault Professor, MCEER
Director Dep. Of Civil, Structural and Environmental Engineering
University at Buffalo State University of New York
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- Design of seismically isolated structures is based on the
mechanical properties of newly-fabricated seismic isolation
hardware Environmental effects, history of loading, aging result in
change in: properties of isolation hardware behavior of isolated
structure Collect field data on the aging characteristics and
long-term service life of seismic isolation bearings
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- Full-Scale Isolated Bridge Calspans Ashford facility, Western
NY 50 miles from UB Two 72-foot long adjacent single lane concrete
girder bridges at a distance of 6 feet 8 low-damping elastomeric
bearings of two different elastomeric compounds Free vibration
testing will be repeated weekly for a period of 5 years starting
end-October 2010 Remotely controlled testing from SEESL/UB
facilities
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- Superstructure Geometry 10 girder beams: AASHTO Box
cross-section (BII-36), 7 0 skew 8 beams weight 26 tons and 2 beams
weight 32 tons longitudinal post-tensioning at bottom plate of
girder beams transverse post-tensioning of girder beams at the
support sections 9 of gravel fill equivalent to 7 concrete/asphalt
deck
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- Abutment Isolation Bearings Girder Beams Gravel Spreader
Beam
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- ashford.wmv
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- Elastomeric Isolators Target period of isolated bridge: T=2 sec
Total weight per bearing: W=100 kips Design deformation: D=4 in 10
low-damping elastomeric bearings of circular cross-section with two
different rubber compounds: Group A -> G=120 psi -> k=2.7
kips/in Group B -> G=70 psi -> k=1.6 kips/in Groups A and B
are assigned to each of the two adjacent bridges Characterization
testing of isolation bearings at SEESL/UB in order to acquire
mechanical properties
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- 20091015-MOV0DF.mpg
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- Bearing Characterization at SEESL Group A k A =2.5 kips/in A
=5% Group B k B =1.5 kips/in B =3%
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- Full-Scale Bridge Testing Actuator Load Cell Actuator spans the
gap between the two adjacent single span bridges Slow extension
rate of the actuator up to: 16 to the reaction load cell 4 design
displacement of the bearings Fast retraction rate of the actuator
in order to subject the two bridges in free vibration
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- Forcing System Properties: Max actuator stroke: 24 in Max
actuator force: 50 kips Group B Group A 4.0 in 2.4 in F=24kips
F=24kips
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- Group A initial displacement: 2.4 in damping: 5% period: 2.0
sec free vibration duration: 35 sec number of cycles: 15 Group B
initial displacement: 4 in damping: 3% period: 2.6 sec free
vibration duration: 70 sec number of cycles: 25
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- Testing Procedure 1.Collect the initial mechanical properties
of the isolation bearings (stiffness, damping) 2.Run bridge free
vibration set of tests remotely from SEESL/UB 3.Collect data/info
from: actuator, reaction load cell accelerometers, load cells,
string potentiometers, thermocouples (26 sensors in total) cameras
weather station 4.Obtain post-testing mechanical properties of
bearings and compare to pre-testing ones 5.Visit the bridge field
station in order to check condition of bearings, actuator,
instrumentation 6.Repeat the procedure weekly and for a period of
five years
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- System Property Modification Factors Properties of seismic
isolation bearings: Characteristic strength, Q d Effective
stiffness, K eff Post-yield stiffness, K d Damping ratio, Phenomena
effecting isolator properties: Temperature Aging Wear or Travel
History of loading Which are the max and min probable values of the
bearing properties within the structures lifetime? Can all
phenomena occur simultaneously?
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- Pn Pn max = max,1 max,2 max,3 min = min,1 min,2 min,3 Bounding
Analysis -factors: quantify the effect of a particular phenomenon
on the nominal properties of an isolation bearing P min = min P n P
max = max P n P max controls the substructure and superstructure
force response P min controls the isolator displacement response
System Property Adjustment factors account for the probability that
several events occur simultaneously, depend on the significance of
the structure and their values are based on engineering judgment
According to AASHTO (1999): The -factors listed herein are based on
the available limited data. In some cases the factors could not be
established and need to be determined by test.
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- max: 80 0 to 100 0 F min: -30 0 to 10 0 F -factors for
Elastomeric Bearings Temperatures for design: 70 0 F to -22 0 F
(AASHTO, 1999) Low temperatures cause increase in stiffness and
strength Duration of exposure is significant but usually neglected
Travel or Wear due to traffic and temperature changes: For a
cumulative movement of 1 mile 17 sets of free vibration tests
should be conducted during one day of testing (AASHTO, 1999)
-factors depend significantly on the rubber compound of the bearing
max,t max,tr
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- Better understanding of the effect of temperature,
environmental conditions and ware on the mechanical properties of
isolation bearings Realistic determination of bounding values of
isolator properties for analysis and design based on better
estimated Property Modification Factors Using different seismic
isolation systems the bridge field station can provide an insight
to the resilience of bridges due to naturally-occurring phenomena
Conclusions
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- Acknowledgments SEESL technical staff and students Doug Stryker
and Andrew Dailey from Calspan H&K Services for constructing
the bridge Hubbell Galvanizing for donating the girder beams
Dynamic Isolation Systems for providing the bearings
- Slide 20
- Thank you! Questions?
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- Instrumentation/DAQ System actuator displacement, load cell
sensors 26 sensors: 10 accelerometers 2 load cells (temperature
range -10F 100F) 10 string potentiometers 4 thermocouples 7 digital
cameras 1 digital weather station 32-channel portable DAQ System
compatible with existing UB/NEES systems and software SEESL remote
desktop controller Ashford host PC/ Pump controller Actuator/Test
DAQ/Sensors Ashford host PC SEESL remote desktop DAQ internet
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- max: 80 to 100F min: -30 to 10F Effects on Elastomeric Bearings
Wear or Cumulative Travel Temperature: low temperatures ->
increase in stiffness and strength high temperatures ->
degradation of the rubber Coupling between wear and temperature
Duration of exposure and elastomeric compound control behavior Lack
of long-term in-situ performance data