EXPERIMENTAL DYNAMIC LOAD ALLOWANCE OF A …
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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.
The Concrete Conventionand Exposition
OUTLINE
➢ Introduction
➢Determination of Impact Factor
➢Bridge A7957
➢Testing Equipment
➢Field Test Procedure
➢Load Test Results
➢Concluding Remarks
The Concrete Conventionand Exposition
➢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
The Concrete Conventionand Exposition
➢Introduction
o Field Tests
𝑹𝑭 =𝑪𝒂𝒑𝒂𝒄𝒊𝒕𝒚 − 𝑫𝒆𝒂𝒅
(𝑮𝑫𝑭)𝑳𝒊𝒗𝒆(𝟏 + 𝑰)
The Concrete Conventionand Exposition
➢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
The Concrete Conventionand Exposition
➢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
The Concrete Conventionand Exposition
➢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
The Concrete Conventionand Exposition
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)
The Concrete Conventionand Exposition
➢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
The Concrete Conventionand Exposition
➢Testing Equipment
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.
.
.
ATS Prism (Target) Accelerometer Laser Vibrometer Target Point
A1
A4
A2
A5
A3
A6
Bridge A7957 instrumentation layout
The Concrete Conventionand Exposition
➢Testing Equipment
Automated Total Station (ATS)
Leica TCA 2003
Accuracy: ±0.1 mm
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.
.
.
ATS Prism (Target) Accelerometer Laser Vibrometer Target Point
A1
A4
A2
A5
A3
A6
The Concrete Conventionand Exposition
➢Testing Equipment
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
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.
.
.
ATS Prism (Target) Accelerometer Laser Vibrometer Target Point
A1
A4
A2
A5
A3
A6
The Concrete Conventionand Exposition
➢Testing Equipment
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
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.
.
.
ATS Prism (Target) Accelerometer Laser Vibrometer Target Point
A1
A4
A2
A5
A3
A6
The Concrete Conventionand Exposition
➢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
The Concrete Conventionand Exposition
➢Field Load Test Description
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
The Concrete Conventionand Exposition
➢Field Load Test Description
Dynamic Load Test
The Concrete Conventionand Exposition
➢Load Test Results
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
The Concrete Conventionand Exposition
➢Load Test Results
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
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.
.
.
ATS Prism (Target) Accelerometer Laser Vibrometer Target Point
A1
A4
A2
A5
A3
A6
Measured acceleration response (96 km/h, west–east direction)
The Concrete Conventionand Exposition
➢Load Test Results
Fundamental Frequency – Fast Fourier Transforms (FFT)
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.
.
.
ATS Prism (Target) Accelerometer Laser Vibrometer Target Point
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
The Concrete Conventionand Exposition
➢Load Test Results
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
The Concrete Conventionand Exposition
➢Load Test Results
Dynamic and Static Vertical Deflection – RSV-150
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
The Concrete Conventionand Exposition
➢Load Test Results
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
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
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
The Concrete Conventionand Exposition
➢Load Test Results
Dynamic and Static Vertical Deflection – RSV-150
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
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
The Concrete Conventionand Exposition
➢ 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.
The Concrete Conventionand Exposition
➢ 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.
The Concrete Conventionand Exposition
Questions ?
Thank you
The Concrete Conventionand Exposition
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]