experimental dynamic load allowance of a …

The Concrete Conventionand Exposition

EXPERIMENTAL DYNAMIC LOAD ALLOWANCE OF A

PRESTRESSED CONCRETE BRIDGE

Eli S. Hernandez, Ph.D.Dr. John J. Myers, Ph.D., P.E.

SESSION: Innovative Techniques for Monitoring and Evaluating Concrete Bridges and Bridge Elements

SPRING 2019 ACI CONVENTIONMarch 24-28, 2019. Québec City, Québec, Canada.


OUTLINE

➢ Introduction

➢Determination of Impact Factor

➢Bridge A7957

➢Testing Equipment

➢Field Test Procedure

➢Load Test Results

➢Concluding Remarks


➢Introduction

o Load Rating

𝑹𝑭 =𝑪𝒂𝒑𝒂𝒄𝒊𝒕𝒚 − 𝑫𝒆𝒂𝒅

(𝑮𝑫𝑭)𝑳𝒊𝒗𝒆(𝟏 + 𝑰)

The strength evaluation procedure employed to obtain the live

load carrying capacity that a bridge structure can withstand

without suffering damage or undergoing collapse

Major basis in prioritizing maintenance operations

Traditional methods: analytical and experimental


➢Introduction

o Field Tests

𝑹𝑭 =𝑪𝒂𝒑𝒂𝒄𝒊𝒕𝒚 − 𝑫𝒆𝒂𝒅

(𝑮𝑫𝑭)𝑳𝒊𝒗𝒆(𝟏 + 𝑰)


➢Introduction

o Objective: to obtain the impact factor of Bridge A7957 analytically and

experimentally in an attempt to quantify differences between both approaches

that are employed in bridge design and evaluation.

Laser Vibrometer Accelerometers Total Station


➢Determination of Impact Factor (Analytically)➢ AASHTO Standard (1992)

𝐼𝑀 =15.24

𝐿 + 38≤ 0.30

➢ AASHTO LRFD (1994)

𝐷𝐿𝐴 = 0.33

➢ Ontario Highway Bridge Design Code (1983 )

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0 1 2 3 4 5 6 7 8 9 10

Dyn

am

ic L

oad

All

ow

an

ce

Fundamental Frequency (Hz)

0.40

0.25


➢Determination of Impact Factor (Experimentally)

𝐼𝑀 = 𝐷𝐿𝐴 =𝑅𝑑𝑦𝑛 − 𝑅𝑠𝑡𝑎

𝑅𝑠𝑡𝑎

The value of IM is commonly defined as the ratio of the

difference of the maximum dynamic and static responses to

the maximum static response


Bridge A7957

Hwy 50 Near Hwy US-63

West of Linn, MO

➢Missouri Bridge A7957

➢ PC/PS NU53 Girders:

Span 1: CC, f’c=8 ksi (55.2 MPa)

Span 2: HS-SCC, f’c=10 ksi (68.9 MPa)

Span 3: NS-SCC, f’c=8 ksi (55.2 MPa)


➢Bridge A7957

Int. Diaphragm

Bent 2 (Class B Concrete)

Bent 1

Bent 3 (HVFAC)

3.25 m

1.32 m Bent 4

Safety Barrier

Safety Barrier

Span 1 (CC) Span 2 (HS-SCC) Span 3 (NS-SCC)

Unit Conversion: 1 ft = 0.3048 m

3.25 m

3.25 m

1.32 m

30.48 m 36.58 m 30.48 m

Skew30°

Abutment 1 Abutment 4Bent 2 Bent 3



Abut. 130.48 m 36.58 m 30.48 m

Bent 3 Midspan Midspan Midspan

Safety BarrierSpan 1-2 (CC) Span 2-3 (HS-SCC) Span 3-4 (SCC)

30°

Bent 2

Abut.4

1

2

4

3.

.

.

[email protected]

ATS Prism (Target) Accelerometer Laser Vibrometer Target Point

A1

A4

A2

A5

A3

A6

Bridge A7957 instrumentation layout



Automated Total Station (ATS)

Leica TCA 2003

Accuracy: ±0.1 mm

Abut. 130.48 m 36.58 m 30.48 m



30°

Bent 2

Abut.4

1

2

4

3.

.

.

[email protected]


A1

A4

A2

A5

A3

A6



Accelerometers

3

ATS Prism Accelerometer

Varying speeds: 10 - 60 mi/h (16-96 km/h)

Sampling rate: 500 Hz

Abut. 130.48 m 36.58 m 30.48 m



30°

Bent 2

Abut.4

1

2

4

3.

.

.

[email protected]


A1

A4

A2

A5

A3

A6



Remote Sensing Vibrometer (RSV-150)

Varying speeds: 10 - 60 mph (16-96 km/h)

Accuracy: ±0.01 mm

Sampling rate: 120 Hz

Abut. 130.48 m 36.58 m 30.48 m



30°

Bent 2

Abut.4

1

2

4

3.

.

.

[email protected]


A1

A4

A2

A5

A3

A6


➢Field Load Test Description

MoDOT H20 truck employed during static and dynamic tests.

Conversion factor: 1 m = 3.28 ft; 1 kN = 0.2248 kip

(171.8 kN = 38.4 kip, 70.6 kN = 15.9 kip)

H-20 DUMP TruckP2

P2

P11.83 m

1.42 m 4.88 m

171.8 kN 70.6 kN

Static Load Test



Static test configurations. Conversion factor: 1 m = 3.28 ft

Static Load Test

15.25 m

1

12

34

Midspan

1

15.25 m

12

34

Midspan

(b) Static Test 2 (Span 3)

(a) Static Test 1 (Span 1)

H-20 DUMP TruckP2

P2

P11.83 m

1.42 m 4.88 m

171.8 kN 70.6 kN

H-20 DUMP TruckP2

P2

P11.83 m

1.42 m 4.88 m

171.8 kN 70.6 kN

Test 1

Test 2



Dynamic Load Test



Static vertical deflection (ATS)

Static Test (Span 1) Prisms Automated Total Station

15.25 m

1

12

34

Midspan

1

15.25 m

12

34

Midspan

-0.118

-0.098

-0.078

-0.058

-0.038

-0.018

0.002

-3.0

-2.5

-2.0

-1.5

-1.0

-0.5

0.0

Def

lect

ion

(in

)

Def

lect

ion

(m

m)

Girder Number

Test 1 (Span 1-2) Test 2 (Span 3-4)

d: 1.9 mm

G1 G2 G3 G4

d: 1.8 mm

3)1)

Test 1

Test 2



Acceleration response (accelerometers)

-0.010

-0.005

0.000

0.005

0 1 2 3 4 5 6 7 8 9 10

Acc

elara

tion

(g)

Time (sec)

Abut. 130.48 m 36.58 m 30.48 m



30°

Bent 2

Abut.4

1

2

4

3.

.

.

[email protected]


A1

A4

A2

A5

A3

A6

Measured acceleration response (96 km/h, west–east direction)



Fundamental Frequency – Fast Fourier Transforms (FFT)

Abut. 130.48 m 36.58 m 30.48 m



30°

Bent 2

Abut.4

1

2

4

3.

.

.

[email protected]


A1

A4

A2

A5

A3

A6

Natural frequency extracted through FFT

0.0004

0.0008

0.0012

0.0016

0 1 2 3 4 5 6 7 8 9 10

Ma

gn

itu

de

Frequency (Hz)

3.125 Hz



Dynamic and Static Vertical Deflection – RSV-150

Maximum static and dynamic deflections

-0.5

0.0

0.5

1.0

1.5

2.0

2.5

2 6 10 14 18 22 26

Mid

span

Def

lect

ion

(m

m)

Time (sec)

Dynamic Quasi-static (filtered) Static (ATS)

Girder 3's static deflection = 1.8 mm

Ddynmax = 2.08 mm

Dfil_stamax = 1.77 mm

𝐼𝑀𝑒𝑥𝑝 = 𝐷𝐿𝐴𝑒𝑥𝑝 =𝐷𝑑𝑦𝑛

𝑚𝑎𝑥 − 𝐷𝑠𝑡𝑎𝑚𝑎𝑥

𝐷𝑠𝑡𝑎𝑚𝑎𝑥




𝐼𝑀𝑒𝑥𝑝 = 𝐷𝐿𝐴𝑒𝑥𝑝 =𝐷𝑑𝑦𝑛

𝑚𝑎𝑥 − 𝐷𝑠𝑡𝑎𝑚𝑎𝑥

𝐷𝑠𝑡𝑎𝑚𝑎𝑥 𝐷𝐴𝐹𝑒𝑥𝑝 = (1 + 𝐼𝑀𝑒𝑥𝑝)

Speed (mi/h) 10 20 30 40 50 60

Ddynmax (mm) 1.77 1.79 1.79 1.77 2.03 2.08

Dfil_stamax (mm) 1.77 1.77 1.77 1.77 1.77 1.77

IMexp 0.000 0.010 0.010 0.000 0.150 0.175

DAFexp 1.000 1.010 1.010 1.000 1.150 1.175

DLA (AASHTO LRFD5) 0.33 0.33 0.33 0.33 0.33 0.33

IM (AASHTO Standard4) * 0.222 0.222 0.222 0.222 0.222 0.222

IM (AASHTO Standard4) † 0.204 0.204 0.204 0.204 0.204 0.204

DLA (OHBDC6) 0.40 0.40 0.40 0.40 0.40 0.40

𝐼𝑀 =15.24

𝐿 + 38≤ 0.30

RF =Capacity − Dead

(GDF)Live(1 + I)

Experimental and analytical impact factor. Conversion factor: 10 mi/h = 16 km/h



Dynamic Load Allowance – OHBDC

Speed (mi/h) 10 20 30 40 50 60

Ddynmax (mm) 1.77 1.79 1.79 1.77 2.03 2.08

Dfil_stamax (mm) 1.77 1.77 1.77 1.77 1.77 1.77

IMexp 0.000 0.010 0.010 0.000 0.150 0.175

DAFexp 1.000 1.010 1.010 1.000 1.150 1.175

DLA (AASHTO LRFD5) 0.33 0.33 0.33 0.33 0.33 0.33



DLA (OHBDC6) 0.40 0.40 0.40 0.40 0.40 0.40

0.0004

0.0008

0.0012

0.0016

0 1 2 3 4 5 6 7 8 9 10

Magn

itu

de

Frequency (Hz)

3.125 Hz

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0 1 2 3 4 5 6 7 8 9 10

Dyn

am

ic L

oad

All

ow

an

ce

Fundamental Frequency (Hz)

0.40

0.25




Speed (mi/h) 10 20 30 40 50 60

Ddynmax (mm) 1.77 1.79 1.79 1.77 2.03 2.08

Dfil_stamax (mm) 1.77 1.77 1.77 1.77 1.77 1.77

IMexp 0.000 0.010 0.010 0.000 0.150 0.175

DAFexp 1.000 1.010 1.010 1.000 1.150 1.175

DLA (AASHTO LRFD5) 0.33 0.33 0.33 0.33 0.33 0.33



DLA (OHBDC6) 0.40 0.40 0.40 0.40 0.40 0.40

0.80

0.90

1.00

1.10

1.20

1.30

0 10 20 30 40 50 60 70 80 90 100Dy

na

mic

Am

pli

fica

tion

Fact

or

Truck Speed (km/h)

Represents 13% difference between DAFs

RF =Capacity − Dead

(GDF)Live(1 + I)

DAF=1.33


➢ Concluding Remarks

➢ The first series of static and dynamic load tests was conducted on Bridge A7957 to

monitor its initial in-service dynamic response.

➢ The impact factor (IM) or dynamic load allowance (DLA) of Bridge A7957 was

obtained from field measurements and using three design specifications. The impact

factors obtained with the design specifications resulted in larger values compared to

the experimental values.

➢ The impact factors obtained from field load tests implicitly take into account in-situ

parameters such as unintended support restraints, unintended continuity, skew

angle, contribution of secondary members and soil-structure interaction which

improve the bridge’s dynamic response.

➢ These factors are not considered by the analytical methods proposed in the current

design and evaluation codes. Consequently, further research needs to be conducted

to quantify the influence of these in-situ parameters on the dynamic response of a

bridge structure.


➢ Acknowledgements

➢ The financial support from the Missouri Department of Transportation and the

National University Transportation Center at Missouri University of Science and

Technology is gratefully acknowledged.

➢ Special thanks are given to the Missouri S&T’s staff members of the CArE

Engineering Department: Brian Swift, Gary Abbott, John Bullock and Jason Cox, as

well as the graduate students: Alexander Griffin, Hayder Alghazali, and Kaylea

Smith.


Questions ?

Thank you


EXPERIMENTAL DYNAMIC LOAD ALLOWANCE OF

A PRESTRESSED CONCRETE BRIDGE

2019 ACI Spring Conference24 March 2019

Quebec, Canada

Eli Hernandez / John J. Myers

Contact: [email protected] / [email protected]

mailto:[email protected]

mailto:[email protected]

experimental dynamic load allowance of a …

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