Shake Table Testing of a Large Scale Two Span R-C Bridge

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Shake Table Testing of a Large Scale Two Span R-C
Bridge
Univ. of Nevada, Reno PI M. Saiid
Saiidi Co-PI David Sanders RA Nathan Johnson

• Univ. of Washington
• PI Marc Eberhard
• Co-PI Pedro Arduino
• Co-PI Steven Kramer
• RA Tyler Ranf

Overall project PI Sharon Wood, Univ. Texas,
Austin
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Outline

• Background information
• Basics of the design
• Construction and assembly
• Instrumentation and test schedule
• Experimental observations/results
• Analytical modeling
• Future work

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Prototype Bridge Frame

• Continuous CIP post-tensioned RC box girder.
• 120 ft span lengths.
• 4 ft circular columns, fixed-fixed.
• Varied column heights.
• Drilled shafts (pile extension as opposed to pile
  cap).
• Axial load index 0.08.

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Shake Table Tests

• 0.25 linear scale (12in dia. Columns)
• Columns fixed at pile point of maximum
• curvature
• Column heights of 5ft, 8ft 6ft
• Input motions soil motion at pile immediately
  below plastic hinge
• Concentrate on column response and interaction in
  global system

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Basics of the Design

• Columns NCHRP 12-49 / Caltrans
• Long. steel ratio 1.56
• Lateral steel ratio 0.86
• Joints not modeled in detail
• Superstructure not modeled in detail
• Convert prototype into equivalent specimen solid
  section

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Inertial/Axial Masses

• 46.5 kip required per column
• Weight Scaled by length3, pressure only by
  length2
• Concrete Blocks 120 kip
• Lead 58 kip

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Superstructure Design

• 2 sets - three 331in x 30in x 14in beams
• Dapped ends
• DL SF 2 (ignore post-tensioning)

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Post-Tensioning

• Longitudinal System
• Prevent cracking in superstructure
• Transverse System
• Maintain beam continuity (90in x 14in)
• Clamping force to prevent beam separation caused
  by transverse lateral moment
• Mass to deck
• Footings to tables

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Construction
A
B
C
D
E
F
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Assembly

• 11 pieces cast separately on and off-site
• Grouted / Post tensioned together
• Imposed mass added

A
B
C
D
E
F
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Instrumentation

• 298 channels _at_ 100Hz

Column lat./long. strain gauges
Shear transducers
Curvature transducers
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• Accelerometers
• Transducers

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Earthquake Motions

• 1994 Northridge Century City
• UC Davis and U. Washington
• 90deg and 180deg components
• Motion transmitted down to bedrock using Proshake
  (83ft)
• Propagated up through medium-dense sand to 2D
  pile depth (equivalent depth of fixity)
• Low amplitude testing (pre-yield) (14 tests)
• Transverse incoherent motions
• Biaxial motions
• Centrifuge motions
• High amplitude testing (to failure) (9 tests)
• From 0.075g to 1.66g PGA

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Transverse modes of bridge
Translation (mode 2) 81.9
Rotation (mode 3) 18
Superstructure Bending (mode 6) 0.1
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High Amplitude Spectra
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Damage Progression
0.5g Significant Flexural Cracks in B1 B3
1.0g Concrete Spalling and first lateral steel
exposure in B1 B3
1.33g long bar exposure in B3
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Damage Progression
1.66g (failure) four spirals fractured, 36
buckled long. bars
1.33g First lateral steel exposure in B2
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Failure test (1.66 PGA)
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Failure Test Bent 3
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Acceleration-Disp. Hysteresis
Tests 12-20 (cumulative) Bent 1 (6 ft
columns) Bent 2 (8 ft columns) Bent 3 (5ft
columns)
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Displacement Ductility
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Test 19 animation 2.5-17.5sec 1x timescale
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Test 19 animation 5-7.5sec 0.2x timescale
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Test 14 Achieved Table Motions
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Test 19 Achieved Table Motions
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Data Processing

• Structural data displacement, acceleration,
  strain, curvature, shear
• Shake table motions
• Accelerations, displacements, spectra
• Videos, photos
• Correlation of force with acceleration
• Extract force from shake tables for select runs

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SAP 2000 Modeling(work in progress)

• Expansion of model used for design / pre-analysis
• Moment-rotation hinges ? Nonlinear fiber hinges
• Model efficiency
• Study the effect of fiber and element
  configurations
• Model parameters
• Material models
• Input motions
• Time-step / integration
• Verification/calibration of model
• Compare accelerations and displacements from
  shake table tests
• Compare with Drain-3DX
• Utilize model to focus on system response

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Test 15 Displacement Predictions
mD 1.52.5
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Test 18 Displacement Predictions
mD 4.15.5
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Test 18 Accel-Disp Predictions
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Future Work

• Complete calibration and verification of
  analytical model
• Investigation of system response utilizing
  experimental data and analytical model
• Expansions of computer model
• More complete system
• Earthquake loading including biaxial motions

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Questions?