Structural Health Monitoring Studies of the Alamosa Canyon and I-40 Bridges

TLDR: In this paper, the authors present the data collected from the various vibration tests performed on the Alamosa Canyon Bridge, analyses of these data, and the results that have been obtained.

Abstract: From 1994 to 1997 internal research grants from Los Alamos National Laboratory's Laboratory Direct Research and Development (LDRD) office were used to fund an effort aimed at studying global vibration-based damage detection methods. To support this work, several field tests of the Alamosa Canyon Bridge have been performed to study various aspects of applying vibration-based damage detection methods to a real world in situ structure. This report summarizes the data that has been collected from the various vibration tests performed on the Alamosa Canyon Bridge, analyses of these data, and the results that have been obtained. Initially, it was the investigators' intent to introduce various types of damage into this bridge and study several vibration-based damage detection methods. The feasibility of continuously monitoring such a structure for the onset of damage was also going to be studied. However, the restrictions that the damage must be relatively benign or repairable made it difficult to take the damage identification portion of the study to completion. Subsequently, this study focused on quantifying the variability in identified modal parameters caused by sources other than damage. These sources include variability in testing procedures, variability in test conditions, and environmental variability. These variabilities must be understood and their influence on identified modal properties quantified before vibration-based damage detection can be applied with unambiguous results. Quantifying the variability in the identified modal parameters led to the development of statistical analysis procedures that can be applied to the experimental modal analysis results. It is the authors' opinion that these statistical analysis procedures represent one of the major contributions of these studies to the vibration-based damage detection field. Another significant contribution that came from this portion of the study was the extension of a strain-energy-based damage detection method originally developed for structures that exhibit beam-bending response to structures that exhibit plate-like bending or bending in two directions. In addition, based on lessons learned from the Alamosa Canyon Bridge test, data from the I-40 Bridge tests have been re-analyzed using the statistical analysis procedures developed as part of this study. The application of these statistical procedures to the I-40 Bridge test results gives particular insight into how statistical analysis can be used to enhance the vibration-based damage detection process.

Figures

Figure C-2. Illustration of angle definition.

Table 10. Relative 95% Uncertainty Level Comparison for Identified Modal Parameters.

Figure 84. The four levels of damage induced by cutting the I-40 plate girder.

Figure 72. Bar plots of the changes in flexibility for the three data sets analyzed.

Table 6. Comparison of two modal analyses of data from Seymour Bridge in Cincinnati, Ohio

Figure 33. Accelerometer, impact, and thermometer locations.

Full text

Los
NATIONAL LABORATORY
Alamos
Los Alamos National Laboratory is operated by the University of California
for the United States Department of Energy under contract W-7405-ENG-36.
LA-13635-MS
Structural Health Monitoring Studies of
the Alamosa Canyon and I-40 Bridges
Approved for public release;
distribution is unlimited.

This report was prepared as an account of work sponsored by an agency of the United States
Government. Neither The Regents of the University of California, the United States
Government nor any agency thereof, nor any of their employees, makes any warranty, express
or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or
usefulness of any information, apparatus, product, or process disclosed, or represents that its
use would not infringe privately owned rights. Reference herein to any specific commercial
product, process, or service by trade name, trademark, manufacturer, or otherwise, does not
necessarily constitute or imply its endorsement, recommendation, or favoring by The Regents
of the University of California, the United States Government, or any agency thereof. The
views and opinions of authors expressed herein do not necessarily state or reflect those of
The Regents of the University of California, the United States Government, or any agency
thereof. Los Alamos National Laboratory strongly supports academic freedom and a
researcher's right to publish; as an institution, however, the Laboratory does not endorse the
viewpoint of a publication or guarantee its technical correctness.
Cover photos: The Alamosa Canyon Bridge and various activities
performed during this study.
An Affirmative Action/Equal Opportunity Employer

Los
NATIONAL LABORATORY
Alamos
Los Alamos, New Mexico 87545
Structural Health Monitoring Studies of
the Alamosa Canyon and I-40 Bridges
Charles R. Farrar
Phillip J. Cornwell*
Scott W. Doebling
Michael B. Prime
Student Participants
Alex Barron, Stanford University
Bethany Carlson, University of California, Berkeley
Randy Goodman, University of Colorado
Gwang-He Heo, University of New Mexico
Marcie Kam, Rose-Hulman Institute of Technology
Erik Straser, Stanford University
Janneane S. Vigil, New Mexico State University
Post-Doctoral Research Associate
Daniel Shevitz
Service Academy Graduate Research Assistant
Lt. Brian Hoerst, USN
*Rose-Hulman Institute of Technology, 5500 Wabash Ave., Terre Haute, IN 47803.
LA-13635-MS
Issued: July 2000

v
TABLE OF CONTENTS
LIST OF FIGURES .....................................................................................................................viii
LIST OF TABLES.........................................................................................................................xi
ABSTRACT.................................................................................................................................... 1
I. INTRODUCTION ....................................................................................................................2
II. DESCRIPTION OF THE ALAMOSA CANYON BRIDGE................................................... 4
III. PRELIMINARY VIBRATION TESTS PERFORMED ON THE ALAMOSA
CANYON BRIDGE................................................................................................................ 12
A. Forced Vibration Tests .......................................................................................................12
1. Roving Hammer Impact Test .........................................................................................12
a. Experimental procedure and equipment.....................................................................12
b. Results of roving hammer impact test........................................................................ 17
2. Single Excitation Point Impact Test Method.................................................................. 20
a. Experimental procedure and equipment.....................................................................20
b. Results of the single excitation point impact test....................................................... 21
B. Ambient Vibration Tests..................................................................................................... 25
1. Ambient Vibration Test Following the Roving Hammer Impact Test...........................25
a. Experimental procedure and equipment.....................................................................25
b. Results........................................................................................................................ 26
2. Ambient Vibration Test Following the Single Excitation Point Test............................. 29
a. Experimental procedure and equipment.....................................................................29
b. Results........................................................................................................................ 29
C. Lessons Learned from the Preliminary Tests ..................................................................... 31
IV. VIBRATION TESTS PERFORMED ON THE ALAMOSA CANYON BRIDGE............... 31
A. Forced Vibration Tests ....................................................................................................31
1. Linearity and Reciprocity Checks .................................................................................. 31
a. Experimental procedure and equipment.....................................................................31
b. Linearity and reciprocity test results..........................................................................34
2. Three-span test................................................................................................................ 39
a. Experimental procedure and equipment.....................................................................39
b. Results from the three-span test.................................................................................39
B. Vibration Tests Performed to Study Variability of Modal Properties................................ 42
1. Results from Tests to Study Variability Caused by Thermal Effects............................. 42
2. Results from Tests to Study Variability Caused by Vehicle Weight .............................45
3. Results from Tests to Study Variability Caused by the Excitation Source .................... 46
4. Results from Tests to Study Variability Caused by Data Reduction.............................. 46
C. Statistical Analysis Methods............................................................................................... 48

vi
1. Monte Carlo Analysis Procedure.................................................................................... 48
2. Bootstrap Analysis Procedure ........................................................................................50
3. Test on Simulated Data................................................................................................... 52
D. A Statistical Comparison of Impact and Ambient Testing Results.................................... 54
1. Description of the Ambient Test ....................................................................................55
2. Description of the Statistical Methods............................................................................ 57
3. Results ............................................................................................................................ 58
E. A Comparison of the Monte Carlo and Bootstrap Techniques...........................................61
1. Application to the Alamosa Canyon Bridge...................................................................61
2. Summary and Observations............................................................................................65
F. Tests to Study Damage Identification................................................................................. 66
1. Simulated Damage Study ............................................................................................... 67
a. Uncertainty bounds on measured parameters from random disturbance................... 67
b. Simulation of damage in the finite element model .................................................... 68
c. Comparison of statistics to predicted damage effects ................................................ 68
2. Stiffening the Structure................................................................................................... 75
a. Results from stiffening the structure.......................................................................... 76
G. Shaker Tests........................................................................................................................ 79
H. A Modular, Wireless Damage Monitoring System (WiMMS) .......................................... 84
V. FINITE ELEMENT MODELING OF THE ALAMOSA CANYON BRIDGE .................... 86
VI. APPLICATION OF STATISTICAL METHODS TO I-40 TEST DATA............................. 89
A. The I-40 Bridge Damage Identification Experiment.......................................................... 90
B. Theoretical Development.................................................................................................... 92
1. Estimation of Random Error in Measured Modal Data..................................................92
2. Monte Carlo Simulation and Application to Modal Parameter Identification ............... 93
3. Damage Identification Using Modal Flexibility Change ............................................... 93
4. Confidence Intervals on Flexibility Damage Indicator .................................................. 94
5. Tests of Significant Difference Between Sample Means............................................... 94
C. Experimental Results, Statistical Analysis, and Discussion............................................... 96
1. Damage Identification Using Measured Flexibility Change........................................ 100
D. Conclusions from the I-40 Bridge Tests...........................................................................101
VII. SUMMARY AND CONCLUSIONS.................................................................................. 102
A. Variability Studies............................................................................................................102
B. Statistical Methods............................................................................................................ 104
C. Damage Assessment of Alamosa Canyon Bridge ............................................................ 104
D. Statistical Damage Assessment of the I-40 Bridge...........................................................105

Frequently asked questions

Q1. What contributions have the authors mentioned in the paper "Structural health monitoring studies of the alamosa canyon and i-40 bridges" ?

To support this work, several field tests of the Alamosa Canyon Bridge have been performed to study various aspects of applying vibration–based damage detection methods to a real world in situ structure. This report summarizes the data that has been collected from the various vibration tests performed on the Alamosa Canyon Bridge, analyses of these data, and the results that have been obtained. Initially, it was the investigators ’ intent to introduce various types of damage into this bridge and study several vibration-based damage detection methods. The feasibility of continuously monitoring such a structure for the onset of damage was also going to be studied. However, the restrictions that the damage must be relatively benign or repairable made it difficult to take the damage identification portion of the study to completion. Subsequently, this study focused on quantifying the variability in identified modal parameters caused by sources other than damage. It is the authors ’ opinion that these statistical analysis procedures represent one of the major contributions of these studies to the vibration-based damage detection field. Another significant contribution that came from this portion of the study was the extension of a strainenergy-based damage detection method originally developed for structures that exhibit beambending response to structures that exhibit plate-like bending or bending in two directions. In addition, based on lessons learned from the Alamosa Canyon Bridge test, data from the I40 Bridge tests have been re-analyzed using the statistical analysis procedures developed as part of this study. Finally, data from the Alamosa Canyon and I-40 Bridge tests along with all reports and papers related to these studies have been made available to other researchers at the following site: http: //ext. lanl. 

Q2. What are the future works mentioned in the paper "Structural health monitoring studies of the alamosa canyon and i-40 bridges" ?

Quantifying the variability in the identified modal parameters led to the development of statistical analysis procedures that can be applied to experimental modal analysis results. The application of the statistical procedures to the I-40 Bridge test results gave particular insight into how statistical analysis can be used to enhance the vibration-based damage detection process. A. Variability Studies Before vibration-based damage identification procedures can be routinely applied to a bridge, particularly in a remote monitoring mode, the effects of variability sources on the modal-based parameters used by the damage identification algorithm must be quantified. Based on the results of the variability tests, it is conceivable that bounds can be developed for the base parameters that could be monitored by a damage identification system. 

Q3. What is the author’s opinion on the Alamosa Canyon Bridge?

It is the authors’ opinion that if vibration-based damage detection technology is to be adopted on a wide scale, then it will have to be used in conjunction with a wireless data acquisition system. 

Q4. What is the purpose of the study?

From 1994 to 1997 internal research grants from Los Alamos National Laboratory’s Laboratory Direct Research and Development (LDRD) office have been used to fund an effort aimed at studying vibration-based damage detection methods. 

Q5. Who has been instrumental in establishing the Alamosa Canyon Bridge as a field test?

Professor Ken White at New Mexico State University and staff from the Alliance for Transportation Research have been instrumental in establishing this bridge as a field test site. 

Q6. What was the main contribution of the study?

Another major contribution that came from this portion of the study was the extension of a strain-energy-based damage detection method to structures that exhibit plate-like bending or bending in two directions. 

Q7. What is the need for additional global damage detection methods?

The need for additional global damage detection methods that can be applied to complex structures has led to the development of methods that examine changes in the global dynamic characteristics of the structure. 

Q8. Where is the Alamosa Canyon Bridge located?

This bridge is located adjacent to Interstate 25 (I-25) approximately 16 km (10 miles) north of Truth or Consequences, New Mexico. 

Q9. What is the author’s opinion on the impact of the I-40 Bridge tests?

It is the authors’ opinion that these statistical analysis procedures represent one of the major contributions of these studies to the vibration-based damage detection field. 

Q10. How many do the LDRD researchers use to study the Alamosa Canyon Bridge?

To support this work, several field tests of the Alamosa Canyon Bridge have been performed to study various aspects of applying vibration–based damage detection methods to a real world in situ structure.