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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 - PowerPoint PPT Presentation
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Bridge Seismic Isolation Study on a Full Scale Bridge Test
Myrto Anagnostopoulou SEESL Structural and Test Engineer
Ricardo Ecker LayPh.D. Candidate
Andre Filiatrault Professor, MCEER Director
Dep. Of Civil, Structural and Environmental EngineeringUniversity at Buffalo – State University of New York
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
Full-Scale Isolated Bridge
Calspan’s 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
Superstructure Geometry
10 girder beams: AASHTO Box cross-section (BII-36), 70 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
Abutment
IsolationBearings
Girder Beams
Gravel
Spreader
Beam
ashford.wmv
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/inGroup 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
20091015-MOV0DF.mpg
Bearing Characterization at SEESL
Group A kA=2.5 kips/in ζA=5%
Group B kB=1.5 kips/in ζB=3%
Full-Scale Bridge Testing
Actuator
LoadCell
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
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
0 10 20 30 40 50 60 70 80 90 100-4
-3
-2
-1
0
1
2
3
4
Time (sec)
Dis
plac
emen
t (in
)
Group B
0 10 20 30 40 50 60 70 80 90 100-2.5
-2
-1.5
-1
-0.5
0
0.5
1
1.5
2
2.5
Time (sec)
Dis
plac
emen
t (in
)
Group A
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
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/UB3. 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
System Property Modification Factors Properties of seismic isolation bearings:
Characteristic strength, Qd
Effective stiffness, Keff
Post-yield stiffness, Kd
Damping ratio, ζ 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 structure’s lifetime?
Can all phenomena occur simultaneously?
Pn
λmax= λmax,1·λmax,2·λmax,3 ···
λmin= λmin,1·λmin,2·λmin,3 ···
Bounding Analysis
λ-factors: quantify the effect of a particular phenomenon on the nominal properties of an isolation bearing
Pmin = λmin·Pn
Pmax = λmax·Pn
Pmax controls the substructure and superstructure force response Pmin 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 λ-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.”
max: 800 to 1000F
min: -300 to 100F
λ-factors for Elastomeric Bearings Temperatures for design: 700F to -220F (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)
λ-factors depend significantly on the rubber compound of the bearing
λmax,t
λmax,tr
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
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
Thank you! Questions?
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/SensorsAshford host PC
SEESL remote desktop DAQ
internet
internet
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