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Coastal Waterway Bridge Instrumentationfor Overload Monitoring
Steve C.S. Cai, Ph.D., P.E.Professor, Edwin B. Norma S. McNeil Distinguished Professor
Dept. of Civil and Environmental EngineeringLouisiana State University, Baton Rouge, LA 70803
Marcio Araujo, Archana Nair, X.Z. Liu, Miao Xia, and X.M., Shi
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Acknowledgments The authors express their thankfulness to the Louisiana
DOTD for providing the necessary personnel and equipment for the execution of the tests. Specifically, thanks go to Arthur D’Andrea, Stephanie Cavalier, Steven Sibley and the other crew members.
The contents of this report reflect only the views of the writers who are responsible for the facts and the accuracy of the data presented herein.
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Outline Introduction to the project
Instrumentation for strain gages
Instrumentation for acoustic emission sensors
Conclusions
Highway LA-1 over the Intracoastal Waterway in Port Allen, Louisiana
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Overload approximately 540,000 pounds
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The tested span is 59 ft long with four steel girders (W36X182) supporting a concrete deck. The girders were spaced at 8 ft 8 in. The girders were bolted to a cross-girder that supports them, which was also bolted to the columns.
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Instrumentation Plan – Strain Gages
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Figure 5 ‐ Instrumentation Plan
Instrumentation Plan – Strain Gages
Strains of girders
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Strain of Girder 1 (8975)
-50-25
0255075
100125150175200225250275300
-20 -10 0 10 20 30 40 50 60 70 80 90
Time (s)
Stra
in (μ
ε)
Sensor 8975
Strain of Girder 2 (8981)
-50-25
0255075
100125150175200225250275300
-20 -10 0 10 20 30 40 50 60 70 80 90
Time (s)
Stra
in (μ
ε)
Sensor 8981
Strain of Girder 3 (8994 & 8998)
-50-25
0255075
100125150175200225250275300
-20 -10 0 10 20 30 40 50 60 70 80 90
Time (s)
Stra
in (μ
ε)
Sensor 8994Sensor 8998
Strain of Girder 4 (8982 & 8986)
-50-25
0255075
100125150175200225250275300
-20 -10 0 10 20 30 40 50 60 70 80 90
Time (s)
Stra
in (μ
ε)
Sensor 8982Sensor 8986
Figure 7 – Overload Strains on Girders
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Strain of Cross Girder (8977)
-50-25
0255075
100125150175200225250275300
-20 -10 0 10 20 30 40 50 60 70 80 90
Time (s)
Stra
in (μ
ε)
Sensor 8977
Figure 8 – Overload Strains on Cross-Girder
Strains of Cross-Girder
Strain of column
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Strain of Column 1 (8990 & 8991)
-150
-125
-100
-75
-50
-25
0
25-20 -10 0 10 20 30 40 50 60 70 80 90
Time (s)
Stra
in (μ
ε)
Sensor 8990Sensor 8991
Strain of Column 2 (8978, 8970, 8976 & 8985)
-150
-125
-100
-75
-50
-25
0
25-20 -10 0 10 20 30 40 50 60 70 80 90
Time (s)
Stra
in (μ
ε)
Sensor 8978Sensor 8970Sensor 8976Sensor 8985
Figure 9 – Overload Strains on Vertical Column Member
Strain of inclined column bracing
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Strain of Brace (8987 & 8999)
-150
-125
-100
-75
-50
-25
0
25-20 -10 0 10 20 30 40 50 60 70 80 90
Time (s)
Stra
in (μ
ε)
Sensor 8987Sensor 8999
Figure 10 – Overload Strains on Inclined Column Member
Strain distributions
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Strain of girders
0255075
100125150175200225
0 1 2 3 4 5Girder Number
Stra
in (μ
ε)
Strain of Cross Girder=195 με (t=14.4 s)Strain of Cross Girder=279 με (t=21.4 s)Strain of Cross Girder=163 με (t=39.5 s)
Figure 11 – Overload Strains on Girders at Different Times
Strain of girders under normal traffic
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Strain of Girder 1 (8975)
-20
0
20
40
60
80
100
120
0 25 50 75 100 125 150 175 200 225 250Time (s)
Stra
in (μ
ε)
Sensor 8975
Strain of Girder 2 (8981)
-20
0
20
40
60
80
100
120
0 25 50 75 100 125 150 175 200 225 250Time (s)
Stra
in (μ
ε)
Sensor 8981
Strain of Girder 3 (8994 & 8998)
-20
0
20
40
60
80
100
120
0 25 50 75 100 125 150 175 200 225 250
Time (s)
Stra
in (μ
ε)
Sensor 8994Sensor 8998
Strain of Girder 4 (8982 & 8986)
-20
0
20
40
60
80
100
120
0 25 50 75 100 125 150 175 200 225 250
Time (s)
Stra
in (μ
ε)
Sensor 8982Sensor 8986
Figure 12 – Normal Traffic Strains on Girders (from 18-wheeler)
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Strain of Cross Girder (8977)
-20
0
20
40
60
80
100
120
0 25 50 75 100 125 150 175 200 225 250Time (s)
Stra
in (μ
ε)
Sensor 8977
Figure 13 – Normal Traffic Strains on Cross- Girders (from 18-wheeler)
Strain of cross beam under normal traffic
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Strain of Column 1 (8990 & 8991)
-70
-60
-50
-40
-30
-20
-10
0
100 25 50 75 100 125 150 175 200 225 250
Time (s)
Stra
in (μ
ε)
Sensor 8990Sensor 8991
Strain of Column 2 (8978, 8970, 8976 & 8985)
-70
-60
-50
-40
-30
-20
-10
0
100 25 50 75 100 125 150 175 200 225 250
Time (s)St
rain
(με)
Sensor 8978Sensor 8970Sensor 8976Sensor 8985
Figure 14 – Normal Traffic Strains on Vertical Column Members (from 18-wheeler)
Strain of column under normal traffic
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Strain of Brace (8987 & 8999)
-70
-60
-50
-40
-30
-20
-10
0
100 25 50 75 100 125 150 175 200 225 250
Time (s)
Stra
in (μ
ε)
Sensor 8987Sensor 8999
Figure 15 – Normal Traffic Strains on Inclined Column Members (from 18-wheeler)
Strain of inclined column bracing under normal traffic
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Strain of girders
0
25
50
75
100
125
0 1 2 3 4 5
Girder Number
Stra
in (μ
ε)
Strain of Cross Girder=86 με (t=26.3 s)Strain of Cross Girder=105 με (t=57.5s)Strain of Cross Girder=45 με (t=168.2 s)Strain of Cross Girder=47 με (t=192.4 s)
Figure 16 - Normal Traffic Strains on Girders at Different Times (from 18-wheelers)
Strain distribution of girders under normal traffic
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Table1- Maximum Strains Comparison G1 G2 G3 G4 Cross
Girder Column1 Column2 Brace
Sensor # 8975 8981 8994 8998 8982 8986 8977 8990 8991 8978 8970 8976 8985 8987 8999 Overload
Strain (με)
203 211 205 205 138 148 279 -118 -130 -119 -93 -101 -85 -40 -40
Normal Traffic Strain (με)
78 113 107 102 94 97 105 -65 -66 -59 -52 -56 -50 -21 -20
Comparison of strains under overload and normal traffic
Instrumentation Plan - Acoustic Emission Sensors
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Figure 6 - Acoustic Emissions R6I-AST Sensor
What is Acoustic emission?
A transient elastic wave generated by rapid release of energy from the source within a material.
Courtesy : www.ndt-ed.org
Acoustic emission sensors
Sensors # 1 and 2 were placed on the mid-span of a girder and sensors # 3 and 4 were positioned at a beam-column joint.
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Qualitative results
Load cases considered are : normal traffic load and Overload
Normal traffic Overload
Hits
Time (sec)
Hits
Time (sec)
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Hits vs Amplitude(dB) <3,4>
0 20 40 60 80 1000
100
200
Hits vs Amplitude(dB) <3,4>
0 20 40 60 80 1000
200
400
Figure 20 - Amplitude distribution - normal traffic phase (left) and overload phase (right)
Quantitative results The intensity chart used for assessing the data from
the steel bridge is designed for metal piping systems. Each zone corresponds to a particular intensity of damage.
Intensity chart for AE data collected from steel bridge
Conclusions – Strain gages
Strains for the overload is 211με on girder 2(1.87 times greater) and for normal traffic is 113με on girder 3.
The maximum tensile strain on cross girder under normal traffic conditions is 105με, while its equivalent is 279με for the overload (2.65 times greater).
For column, the maximum compressive strain under normal traffic conditions is 66με, while for the overload is 130με(1.97 times greater).
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Conclusions –Acoustic emission
The structures response of acoustic emission to overload though slightly greater is not significantly different from normal traffic condition response.
All of the results tend to imply that the structural health of the bridge is not a major concern at this time.
Further continuous monitoring of the bridge using many more acoustic sensors may help to avoid concerns with the structure’s integrity in the future.
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