Shake Table Testing of a Large Scale Two Span R-C Bridge Univ. of Washington *PI: Marc Eberhard Co-PI: Pedro Arduino Co-PI: Steven Kramer RA: Tyler Ranf.

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

Univ. of Washington*PI: Marc EberhardCo-PI: Pedro ArduinoCo-PI: Steven KramerRA: Tyler Ranf

Univ. of Nevada, Reno*PI: M. “Saiid” SaiidiCo-PI: David SandersRA: Nathan Johnson

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

Outline

• Background information

• Basics of the design

• Construction and assembly

• Instrumentation and test schedule

• Experimental observations/results

• Analytical modeling

• Future work

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.

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

Mult

Mult

V

linear soil pressure

Hclear

Hcol

Ground

Mult

Mult

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

90in [2286mm]14in [356mm]

Inertial/Axial Masses• 46.5 kip required per column• Weight Scaled by length3, pressure only by length2

– Concrete Blocks = 120 kip

– Lead = 58 kip

Bent 1 Bent 2

Elevation View

Top View

Bent 3

Superstructure Design

• 2 sets - three 331in x 30in x 14in beams

• Dapped ends

• DL SF = 2 (ignore post-tensioning)

8.5in [216mm]8.5in [216mm]

4in [102mm]

15in [381mm]

8in [203mm]

7in [178mm] 15in [381mm]

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

ConstructionAA

BB CC

DD EE FF

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

AA BB CC

DD EE FF

Instrumentation

• 298 channels @ 100Hz

Column lat./long. strain gauges

Shear transducers

Curvature transducers

• Accelerometers

• TransducersNOTES:

= Out of PlaneMeasurement

= DisplacementMeasurementDirection

Bent 1 Bent 2 Bent 3

Top View

Elevation View

NOTES:

= Out of PlaneMeasurement

= AccelerationMeasurementDirection

Bent 3Bent 2Bent 1

Elevation View

Top View

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

Transverse modes of bridgeTranslation (mode 2) 81.9%

Rotation (mode 3) 18%

Superstructure Bending (mode 6) 0.1%

-2

0

2

Bent 1 Bent 3Bent 2

-2

0

2Bent 1 Bent 3Bent 2

-3

0

3

-400 -300 -200 -100 0 100 200 300 400

Superstructure Location (in)

Bent 1 Bent 3Bent 2

High Amplitude Spectra

0

2

4

6

8

0 0.25 0.5 0.75 1

Period (seconds)

Acc

eler

atio

n (g

)

Motion 1, 0.075g to 1.66g PGA

mode2

mode3

mode6

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

Damage Progression

1.33g: First lateral steel exposure in B2

1.66g (failure): four spirals fractured, 36 buckled long. bars

Failure test (1.66 PGA)

Failure Test Bent 3

Acceleration-Disp. Hysteresis

-0.75

-0.50

-0.25

0.00

0.25

0.50

0.75

-5 -4 -3 -2 -1 0 1 2 3 4 5

Column Deflection (in)

-127 -102 -76 -51 -25 0 25 51 76 102 127Column Deflection (mm)

Sup

erst

ruct

ure

Acc

eler

atio

n (g

)

-0.75

-0.50

-0.25

0.00

0.25

0.50

0.75

-5 -4 -3 -2 -1 0 1 2 3 4 5

Column Deflection (in)

-127 -102 -76 -51 -25 0 25 51 76 102 127Column Deflection (mm)

Sup

erst

ruct

ure

Acc

eler

atio

n (g

)

-0.75

-0.50

-0.25

0.00

0.25

0.50

0.75

-5 -4 -3 -2 -1 0 1 2 3 4 5

Column Deflection (in)

-127 -102 -76 -51 -25 0 25 51 76 102 127Column Deflection (mm)

Sup

erst

ruct

ure

Acc

eler

atio

n (g

)

Tests 12-20 (cumulative)

Bent 1 (6 ft columns)

Bent 2 (8 ft columns)

Bent 3 (5ft columns)

Displacement Ductility

-0.75

-0.50

-0.25

0.00

0.25

0.50

0.75

-5 -4 -3 -2 -1 0 1 2 3 4 5

Column Deflection (in)

-127 -102 -76 -51 -25 0 25 51 76 102 127Column Deflection (mm)

Supe

rstru

ctur

e Ac

cele

ratio

n (g

)

Test Bent 1 Bent 2 Bent 3

12 0.35 0.21 0.2113 0.96 0.52 0.5214 1.14 0.68 0.8315 2.37 1.53 2.4516 3.98 2.81 3.1617 2.99 2.38 2.3918 4.20 4.12 5.5419 5.33 5.22 7.9020 3.40 3.77 5.84

displacement ductility

Test 19 animation 2.5-17.5sec 1x timescale

Test 19 animation 5-7.5sec 0.2x timescale

Test 14 Achieved Table Motions

-0.4

-0.2

0

0.2

0.4

0 1 2 3 4 5 6 7 8 9 10

Time (sec)

target

Ta

rge

t A

cc

ele

rati

on

(g

)

-0.4

-0.2

0

0.2

0.4

0 1 2 3 4 5 6 7 8 9 10

Time (sec)

Table 1Table 2Table 3

Ac

hie

ve

d A

cc

ele

rati

on

(g

)

-2

-1

0

1

2

0 1 2 3 4 5 6 7 8 9 10

Time (sec)

target

Ta

rge

t A

cc

ele

rati

on

(g

)

-2

-1

0

1

2

0 1 2 3 4 5 6 7 8 9 10

Time (sec)

Table 1Table 2Table 3A

ch

iev

ed

Ac

ce

lera

tio

n (

g)

Test 19 Achieved Table Motions

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

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

Test 15 Displacement Predictions = 1.5~2.5

-2.0

0.0

2.0

-51

0

51

measured SAP prediction D3DX prediction

Ben

t 1

-2.0

0.0

2.0

-51

0

51

measured SAP prediction D3DX prediction

Ben

t 2

Def

lect

ion

(in)

Def

lect

ion

(mm

)

-2.0

0.0

2.0

-51

0

51

measured SAP prediction D3DX prediction

Ben

t 3

Test 18 Displacement Predictions = 4.1~5.5

-4.0

0.0

4.0

-102

0

102

measured SAP prediction D3DX prediction

Ben

t 1

-4.0

0.0

4.0

-102

0

102

measured SAP prediction D3DX prediction

Ben

t 2

Def

lect

ion

(in)

Def

lect

ion

(mm

)

-4.0

0.0

4.0

-102

0

102

measured SAP prediction D3DX prediction

Ben

t 3

Test 18 Accel-Disp PredictionsMeasured

-0.75

0.00

0.75

-127 0 127Column Deflection (mm)

To

p A

cce

lera

tion

(g

)

Ben

t 1

SAP2000

-127 0 127

Column Deflection (mm)

-0.75

0.00

0.75

-5 0 5Column Deflection (in)

To

p A

cce

lera

tion

(g

)

Ben

t 3

D3DX

-127 0 127

Column Deflection (mm)

-0.75

0.00

0.75

To

p A

cce

lera

tion

(g

)

Ben

t 2

-5 0 5Column Deflection (in)

-5 0 5Column Deflection (in)

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