Lessons from Recent Laboratory and Field Instrumentation Projects

Vellore S. Gopalaratnam, Ph.D., P.E. Visiting Professor, Indian Institute of Technology-Madras Professor of Civil Engineering, University of Missouri-Columbia March 26, 2015 Indian Institute of Science (IISc), Bengaluru

Organization

• Introduction • Bridge Instrumentation Steel Orthotropic Deck Temp-Varying Fatigue Tests HPC Prestressed Girders

• Pavement Project Precast Pre-/Post-Tensioned

• Dam Instrumentation Tainter Gate Instrumentation

• Lessons Learnt

Experimental measurements…

Strain Measurements on Steel Deck

Develop strain time-histories and histograms for laboratory fatigue simulations of steel-wearing surface composite specimens:

Poplar Street Bridge, St. Louis (MO)

Wearing Surfaces: Service Strains

Nicolet digital storage oscilloscope with strain gage amplifier/conditioners

PC-based data acquisition system with safe sequential powering up

Idealized Analyses of Transverse Bending

Yielding

supports

Position wheel loads

for maximum effect

Investigate stresses

and deflections due

to yielding support

Wheel load

Wearing surface

Deck plate (a)

(b)

(c)

Combined Fatigue/Thermal Loading

8000006000004000002000000

0.0

0.2

0.4

0.6

0.8

1.0

1.2

0

750

1500

2250

3000

3750

4500

Relative stiffness

Upper limit loadL

oad

, P

(lb

s)

Number of cycles, N

Fig. 6 Relative stiffness (stiffness relative to initial stiffness at 0° F) versus the number of fatigue cycles in a cold-temperature fatigue test. Progressively increasing upper limit load is also shown in the figure.

Rel

ativ

e st

iffn

ess,

s

First detection

of cracking

Polymer concrete - Steel plate

composite specimen

Transpo T-48

Tem

per

ature

, T

(°F

)

6543210

0.0

0.2

0.4

0.6

0.8

1.0

1.2

0

75

150

225

300

375

450

Relative stiffness

Temperature

Number of cycles, N (millions)

Fig. 5 Temperature corrected relative stiffness versus the number of fatigue cycles. Thermal loading applied simultaneously with the 5 Hz fatigue loading is also shown in the figure.

Polymer concrete - Steel plate

composite specimen

Transpo T-48

First detection

of cracking

Rel

ativ

e st

iffn

ess,

s

Upper Limit

Load: 1,450 lbs

Temperature Varying Laboratory Fatigue Tests on Bridge Composites Investigate static and flexural fatigue performance of composite specimens simultaneously subjected to thermal loading Poplar St. Bridge, St. Louis

Bronx-Whitestone Bridge, NY

San-Mateo Hayward Bridge, San Francisco

Flexural Test Set-Up

Flexural Set-Up Schematic

Flexural Test Set-Up

Automated Digital Imaging System Regular Observation of Cracks

Apparent Flexural Modulus Static Tests

Wearing Surface and Steel Stresses Influence of Temperature (EA)

Wearing Surface and Steel Stresses Influence of Temperature (PC)

Rate of Loading Effect (EA)

Cold Temp Fatigue Results (PC)

Cold Temp Fatigue Results (PC)

Room Temp Fatigue Results (PC)

Room Temp Fatigue Results (PC)

Room Temp Fatigue Results (PC)

Wearing Surfaces: Pull-Out Test

Wearing Surfaces: Resistivity Test

Infrared and Video Images

Patch

Poplar St. Bridge, St. Louis, MO

4”

2”

9 @ 2”

2 @ 2”

4”

2”

9 @ 2”

2 @ 2”

Typical Location of:

• Strain-Gaged Bars

• Vibrating Wire Gages

• Thermistors

Typical

Location of:

• Thermocouples

Bent 1 Bent 2 Bent 3 Bent 4 Bent 5

North (Direction of Traffic)

Girder SI

Girder SX Girder LX Girder LI (G7) (G6) (G1)

(G2)

Instrumented Cross-Section

Prestressed HPC Bridge Girders

•Vibrating Wire Gage •Rugged, long-term stability, insensitive to noise, simultaneous temperature measurement, ideal for long-term strain measurements

•Instrumented Rebar •Electrical resistance strain gages, full-bridge circuit, temperature compensated, prone to drift, sensitive to noise, suitable only for short-term strain measurements

SG1, VW1 T1, T2, T3

SG2, VW2

SG3, SG4 VW3, VW4 T6, T7, T8

T5

T4

Typical instrumentation at one girder cross-section

Curing Temperatures

0

10

20

30

40

50

60

70

-10 0 10 20 30 40 50 60

Elapsed Time from the End of Concrete Placement (Hr)

Te

mp

era

ture

(o C

)

32

52

72

92

112

132

152

SIE-T1

SIE-T2

SIE-T5

SIE-T8

o F

T1 T2

T3

T4

T8 T7 T6 T5

Strains During Curing

-600

-500

-400

-300

-200

-100

0

100

-10 0 10 20 30 40 50 60

Elapsed Time from the End of Concrete Placement (Hr)

Ap

pa

ren

t Str

ain

( st

r)

SXE-S1

SXE-S2

SXE-S3

SXE-S4

S1

S2

S3

S4

PRESTRESS TRANSFER

Straight Strands

-500

-400

-300

-200

-100

0

100

0 2 4 6 8 10 12 14 16 18

Elapsed Time (min)

Str

ain

(

str

)

SIM-S1

SIM-S2

SIM-S3

SIM-S4

S1

S2

S3

S4

Residual Stress Profile

Max. stress of 440 psi

Avg. tensile stress in the web of 190 psi

Type VI HPC Girder Residual Stress Profile

LOAD TEST

Quasi-Static Load Test

Daily Strain Variations

Service Strains - Increasing Temperature

-700

-600

-500

-400

-300

-200

-100

0

100

200

0 10 20 30 40 50 60 70 80 90 100

Time, (days)

Str

ain

, (

)

0

5

10

15

20

25

30

35

Te

mp

era

ture

, Co

V1 V2 V3 T4

March 16, 1999 4:00pmApril May June

Slope

V1 = -1.03 V2 = -0.86 V3 = -0.81

V1

V2

V3

T4

Service Strains - Decreasing Temperature

-700

-600

-500

-400

-300

-200

-100

0

100

0 10 20 30 40 50 60 70 80 90 100

Time, (days)

Str

ain

, (

)

0

4

8

12

16

20

24

28

32

36

Te

mp

era

ture

, Co

V1 V2 V3 T4

August 4, 1999 4:00pm September October November

Slope

V1 = 0.48 V2 = 0.22 V3 = 0.14

V1

V2

V3

T4

Precast Prestressed Pavement

• Evaluate the performance of precast prestressed panels during fabrication, construction and service:

Joint FHWA / MODoT Project

Site – Northbound I-57, existing pavement has been in poor shape for nearly a decade.

1,000’ of precast pavement

Heavy truck traffic

Severe environmental conditions (temperature, deicing, precipitation)

Instrumented Precast Sections

Traffic Direction

Instrumented Test Section

• Divided into four – 250’ sections of 25 slabs each

• All slabs pre-tensioned transversely at the yard

• Each 250’ section was post-tensioned at the site

Pavement Design

• Comprises three panel types: joint, base, and anchor panels

Joint Panel Base Panel

(Multiple)

Anchor

Panel Base Panel

(Multiple)

Joint Panel

Traffic Flow

Typical Panel Design & Instrumetation Layout

• Panels are 10’ by 38’ • Prestressed in the transverse direction and post-

tensioned longitudinally • Stabilized base with polyethylene sheeting for friction

reduction

Anchor Panel 1 (C1) & Base Panels (B1 & B2)

VWG ThermocoupleInstrumented Rebar

Inside Shoulder Outside Shoulder

Pretensioned Strands (8@1’3”)

38’

10’

Junction Box

Post-Tensioning Ducts (18@2’)

Blockout for Strandmeter

Traffic Direction

X3 X3

Anchor Panel 1 (C1) & Base Panels (B1 & B2)

VWG ThermocoupleInstrumented Rebar

Inside Shoulder Outside Shoulder

Pretensioned Strands (8@1’3”)

38’

10’

Junction Box

Post-Tensioning Ducts (18@2’)

Blockout for Strandmeter

Traffic DirectionTraffic Direction

X3 X3

Casting

Casting of Joint Panel

Strandmeter

Instrumentation

Instrumented Rebar

Vibrating Wire Gage

Thermocouples

-60

-50

-40

-30

-20

-10

0

10

0.0 0.5 1.0 1.5 2.0Elapsed Time During Prestressing Stress Transfer, t (Min)

Str

ain

,

( str

ain

)

C1_R3

Theoretical

1

4 5

8 7

6 3 2

Vibrating Wire Gage

Instrumentation Plan

Traffic

Direction

Thermocouple Instrumented Rebar

Insid

e S

ho

uld

er

Ou

tsid

e S

ho

uld

er

T4-5 T1-3

R2 R1

Strandmeter

R4 R3

V2

R5

V1

A

A

Section A: Transfer Sequence

12

3

4

5

6

7

8

Pretension Stress Transfer

Construction

Strandmeter During Post-tensioning

0

1000

2000

3000

4000

5000

6000

7000

8000

Str

ain

,

( str

ain

)

B1_S

B3_S

C1_S

Theoretical (Strain @ 0.80*fpu)

Strain Expected from Pi (0.80fpu)

Relaxation

Stress

ing

Lost Strain- Strandmeter

Bumped Concrete

250’

Active Jacking End

C1_S B1_S

125’ 30’ 80’

B3_S

Section

• Prestressing force lost in PT ducts = 61.8 lb/ft/duct

-50

-40

-30

-20

-10

0

10

0 10 20 30 40 50 60 70 80Time, t (Min)

Str

ain

,

( s

tra

in)

C1_R4

B1_R4

B2_R4

B3_R4

Theoretical

A32 B3

Section 3

B4 B2 B1 C1 A31

2 2 3 4 5 6 7 8 9 10 1 4 5 6 7 8 9 10

Post-Tensioning Stress Transfer Sequence and Rebar Locations

R4, S R2 R1 R5

1

23

4

5

6

7

8

9

10

Post tensioning concrete strain at center of crown (R4)

Service Performance Medium Window

Trends

Increase in temperature = 8 C

Increase in relative strain = 52 mstrain

52 / 8 = 6.5 (Close to CTEconcrete as assumed of 6.0)

15

20

25

30

35

40

45

50

0 24 48 72 96 120 144

Te

mp

era

ture

, T

(°C

)

59

69

79

89

99

109

119

Te

mp

era

ture

, T

(°F

)

C1_T1

C1_T2

C1_T3

C1_T4C1_T5

Ambient Temp

C1_Average Temp

-40

-20

0

20

40

60

80

100

0 24 48 72 96 120 144Time, t (Hrs)

Str

ain

,

(

str

ain

)

C1_R2

C1_R4

Theoretical

Vibrating Wire Gage

Instrumentation Plan

Traffic

Direction

Thermocouple Instrumented Rebar

Insid

e S

ho

uld

er

Ou

tsid

e S

ho

uld

er

T4-5 T1-3

R2 R1

Strandmeter

R4 R3

V2

R5

V1

Service Performance Short Term Window

10

20

30

40

50

24 36 48 60

Te

mp

era

ture

, T

(°C

)

50

68

86

104

122

Te

mp

era

ture

, T

(°F

)

B4_V1t

B4_V2t

Ambient Temp

-50

0

50

100

150

24.0 36.0 48.0 60.0Time, t (Hours)

Str

ain

,

(

str

ain

)B4_R1B4_R2B4_R4B4_R5TheoreticalB4_Average

Vibrating Wire Gage

Instrumentation Plan

Traffic

Direction

Thermocouple Instrumented Rebar

Insid

e S

ho

uld

er

Ou

tsid

e S

ho

uld

er

T4-6 T1-3

R2 R1 R4 R3

V2

R5

V1

T7

Vehicle Response Traffic Response

-2

-1.5

-1

-0.5

0

0.5

1

1.5

2

108 109 110 111 112 113 114

Time (Seconds)

Str

ain

(m

str

ain

)

B4_Rebar 4

Located at crown

3 3/4" from top

surface of

pavement

Environmental Issues

• Heat • Moisture • Lightning

Folsom Dam Failure Tainter Gate Failure

Mf

1

2

3

1. Moment developed from trunnion

friction.

2. Bracing fails because of stress

overload

3. Strut Buckles

Carlyle Lake Dam

Reusable Strain Transducer .4.25”

6”

.125”

Wheatstone Bridge

A

Detail A

.125”

+

A R1 R3

D VG B

R2 Rx

C

-

Gage Locations

Gage Locations

Installing Strain Gages

Instrumentation

LabView Program

Typical Results (smoothed) S

tra

ins,

(

str

ain

s)

Time, t (Clock Time)

to 0.8ft

@ 0.8ft

to 1.4ft

@ 1.4ft

to 0.8ft

@ 0.8 ft

to 0.0ft

@0.0ft

-0.2

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

-60

-40

-20

0

20

40

60

80

11:54:14 AM 11:54:58 AM 11:55:41 AM 11:56:24 AM 11:57:07 AM 11:57:50 AM 11:58:34 AM 11:59:17 AM 12:00:00 PM 12:00:43 PM

Gage 3

Gage 4

Gage 11

Gage 12

Time

Ga

te O

pe

nin

g,

h (

ft)

Typical Results (smoothed) S

tra

ins,

(

str

ain

s)

Time, t (Clock Time)

Ga

te O

pe

nin

g,

h (

ft)

to 0.8ft

@ 0.8ft

to 1.4ft

@ 1.4ft

to 0.8ft

@ 0.8 ft

to 0.0ft

@0.0ft

-0.2

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

-45

-35

-25

-15

-5

5

15

25

35

11:54:14 AM 11:54:58 AM 11:55:41 AM 11:56:24 AM 11:57:07 AM 11:57:50 AM 11:58:34 AM 11:59:17 AM 12:00:00 PM 12:00:43 PM

Gage 13

Gage 14

Gage 15

Gage16

Gate Closing

Lessons Learnt Summary Observations (1/2)

• Know signal content – amplitudes, profile histories, and frequency content

• Identify differential and RSE signals • Adequate planning, documentation, calibration

and labeling of channels • Pictures and video with audio commentary • Redundant instrumentation • Power supply and back-up/start-up logistics • Understand ground signals to avoid spurious

loops • Shielding to mitigate electromagnetic noise • Temperature compensation?

Lessons Learnt Summary Observations (2/2)

• Dust protection to secure electronics • Moisture protection – condensate, drains and

desiccants • Fusing to avoid voltage spikes • Grounding for lightning protection • Cooling of electronic circuitry for optimum

performance • Robust graphical visualization software to allow

better data screening and manipulation

Ignorance IS Bliss!?