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)

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-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)

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Time (s)

Stra

in (μ

ε)

Sensor 8981

Strain of Girder 3 (8994 & 8998)

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Time (s)

Stra

in (μ

ε)

Sensor 8994Sensor 8998

Strain of Girder 4 (8982 & 8986)

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Time (s)

Stra

in (μ

ε)

Sensor 8982Sensor 8986

Figure 7 – Overload Strains on Girders

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Strain of Cross Girder (8977)

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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)

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-75

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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

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-75

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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)

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-125

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-75

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-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

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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)

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0

20

40

60

80

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120

0 25 50 75 100 125 150 175 200 225 250Time (s)

Stra

in (μ

ε)

Sensor 8975

Strain of Girder 2 (8981)

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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)

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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)

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0

20

40

60

80

100

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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)

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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)

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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)

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-60

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-40

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-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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