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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 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

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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