UCBCALTRANS Shaking Table Test of Concrete Bridge Columns

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UCB/CALTRANS Shaking Table Test of Concrete
Bridge Columns
U.C. Berkeley / Caltrans
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RC Column Research

• Main research focus is on Circular Reinforced
  Concrete Bridge Columns

Steel Bar
BRIDGE
COLUMN
SECTION
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Earthquake Shaking
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PEER/Caltrans Bridge Research

• Research Focus
• Monolithic reinforced concrete bridge
  construction
• New rather than older construction detailing
• Representative of
• Viaducts
• Overcrossings
• Major interchanges

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Shaking Table Tests Objectives

• Data to validate analytical models
• Compare performance for near-fault and
  long-duration excitations
• Assess effects of multiple components of ground
  motion
• Assess cumulative damage models

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(No Transcript)
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Specimen Design - Summary

• Aspect Ratio 6 (to center of mass)
• Scale 4.5
• Diametermodel 16
• Use actual mass for axial load
• Unidirectional and bidirectional Input
• Total 4 columns
• longitudinal steel ratio of 1.2 (12 4 bars)
• Spiral reinforcement ratio of 0.54
• Designed according to Caltrans BDS

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Section Details
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Earthquake Histories

• Investigate the response to Unidirectional Vs.
  Bidirectional Loading
• Investigate the effects of Directivity and
  Duration

Near fault record (directivity, short duration)
Large magnitude earthquake (long duration, more
cycles)
Vs
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Test Matrix
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Loading History
Design Level Earthquake (aftershock)
Free Vibration Test
Low Level Testing up to Yield
Maximum Level Earthquake
Design Level Earthquake
Repeat Maximum Until Failure!
Maximum Level Earthquake
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Specimen A2 - Before Testing
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Specimen A2
Design Level 1
Maximum Level 1
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Specimen A2
4th Run at the Maximum Level
dground 4.7,1.3
dmax 7.5, 2.4
aground 1.02g,1.09g
amax 0.24g,0.41g
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Specimen A2 - Final Run
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Damage - Spec A2
After sixth repetition of Maximum Run - Olive View
Fractured Bar
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All Column Exhibited Stable Ductile Behavior
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No Deterioration of Reponse Under Bidirectional
Loading
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Second Mode Effects Due to Mass Rotational Inertia
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Bidirectional Moment Interaction
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Evaluation of Damage Indices
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Column Stiffness Deteriorates Significantly Due
to Shaking
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Verification of Analytical Models

• Response quantities

• Analytical Models
• Elastic Analysis with equivalent sectional
  Stiffness (EI e)
• Concentrated hinge models with equivalent plastic
  hinge properties
• Fiber models with distributed section properties
  with equivalent material properties

• Global
• Displacements,
• Residual Displacements,
• Forces, Moments

• Local
• Curvatures,
• Strains,
• Slip Rotations,
• Cumulative Damage

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Elastic Models

• Various assumptions for approximating effective
  section stiffness EI
• EIe as defined by Caltrans gives reasonable
  results for maximum displacement

EIe
Test
Maximum Credible
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Elastic Models

• Various assumptions for approximating effective
  section stiffness EI
• EIe as defined by Caltrans gives reasonable
  results for maximum displacement
• Not always

EIe
Test
Maximum Credible
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Elastic Models

• Various assumptions for approximating effective
  section stiffness EI
• EIe as defined by Caltrans gives reasonable
  results for maximum displacement
• Not always

EIe
Test
Maximum Credible
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Elastic Models

• Various assumptions for approximating effective
  section stiffness EI
• EIe as defined by Caltrans gives reasonable
  results for maximum displacement
• Not always
• No information on residual displacements
• Other engineering demand parameters inferred from
  pushover analyses

EIe
Test
Maximum Credible
Design Level
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Concentrated Plastic Hinge Models

• Various methods for estimating equivalent
  properties for concentrated plastic hinge (Lp,
  M-f, etc.)
• Various idealized hysteretic models
• Bilinear vs. Stiffness Degrading
• Coupled and uncoupled

Bilinear Stiffness Degrading
Maximum Credible
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Concentrated Plastic Hinge Models

• Most models provide adequate estimate of maximum
  displacement

Bilinear Stiffness Degrading
Maximum Credible
Bilinear Stiffness Degrading
Design Level
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Concentrated Plastic Hinge Models

• Most models provide adequate estimate of maximum
  displacement
• Nonlinear models provide indication of yielding
  and degradation on wave form and residual
  displacement
• Estimates are often poor
• Stiffness degrading models generally better

Bilinear Stiffness Degrading
Maximum Credible
Lateral Direction
Stiffness Degrading Bilinear
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Concentrated Plastic Hinge Models
Bilinear Stiffness Degrading
Maximum Credible
Lateral Direction
Stiffness Degrading Bilinear
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Concentrated Plastic Hinge Models

• Local information on strains, bar buckling,
  fatigue, etc. must be inferred from detailed
  analysis of member
• Problem under cyclic loads?

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Fiber Models

• Useful for well confined members controlled by
  ductile yielding
• Approximations at material level, number of
  fibers used to model section, manner in which
  member is discretized longitudinally

Concentrated Hinge Models
Bilinear Stiffness Degrading
Fiber Model
Maximum Credible
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Fiber Models
Fiber Model
Maximum Credible

• Generally, much better fidelity
• Results, especially for residual displacement and
  local deformations (strain) sensitive to modeling
  of section
• Fixed end rotations due to bar pullout not yet
  accounted for in OpenSees

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Parametric Study

• Design multiple columns with varying

• Diameter (Dcol)

• Axial Load (Pr)

• Aspect Ratio (ar)

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Design Procedure
Sa
Z?? BDS Z4 for all T ATC-32 Z1 to 4
Tlt1 sec Z4 Tgt1 sec SDC
Sa gt 0.1g DcapacitygtDdemand
Elastic ARS Spectrum
Z
Sadesign Sa/Z
0.1g
Period, T
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Automated Design Using Section Properties Database
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Designed Columns with Dcol60
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Ground Motions

• Used 20 LMSR motions

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Hysteretic Model Used
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Performance Evaluation

• Damage Indices

• Park Ang

• Bar Fatigue Damage Index

where 2Nf is the number of half cycles to
failure at a plastic strain
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Mean Results
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Mean1 SD Results
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Comparison of displacement demand
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Low-Cycle Fatigue Index
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Fragility Curves

• For a single column, run suite of ground motions.

• Ground motions are scaled to have a spectral
  acceleration at the period of the column ranging
  from zero to 2 SaARS(Tcol)

• Compute Fragility curves for
• Park Ang Index (Minor and Significant damage)
• Fatigue Index
• Spalling (ecu gt 0.009)

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Fragility Curves for Events with Large Magnitude
at Small Distance
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Fragility Curves for Events with Large Magnitude
at Large Distance