Case Study: Austrian S101 Highway Bridge - Chapter 2
The information described in this case study is by
courtesy of the European research projects “Integrated European
Industrial Risk Reduction System (IRIS)” and “Internet based Structural
Monitoring System (ISMS)”. Special thanks to H. Wenzel
(VCE), M. Döhler (Inria), L. Mevel (Inria) and F. Hille (BAM).
Special thanks to H. Wenzel (VCE), M. Döhler (Inria), L. Mevel (Inria) and F. Hille (BAM).
This case study demonstrates the use of the new Structural Health Monitoring plug-in being developed for the ARTeMIS Modal Pro Software. The measurements used are from the S101 highway overpass bridge located in Reibersdorf, Austria. The bridge crossed the national highway A1 Westautobahn Austria. It is a post-tensioned concrete bridge with a main span of 32 m, side spans of 12 m, and a width of 6.6 m. The deck is continuous over the piers and is built into the abutments. The bridge, built in 1960, had to be demolished due to some structural problems and to allow some space for additional lanes of the highway underneath.
Within the IRIS project, the bridge was artificially damaged in various ways. The damaging processes - listed above to the right - were accompanied by a permanent measurement of the static and dynamic behavior of the structure. The measurements were carried out by VCE and the University of Tokyo on December 10-13, 2008. The data acquisition system had 45 channels. Measurement records were dumped continuously, and each file contained 165,000 samples. In total, this case study consists of 689 of these records. Within the IRIS and the ISMS project, the acquired dynamic measurements have been used to validate the developed damage detection and damage localization techniques.
The objective of this second chapter is to describe the Damage Detection feature of the Structural Health Monitoring plug-in.
New ARTeMIS Feature - Statistical Subspace-based Damage Detection
For a long time, the trend has been to check the health of a structure by comparing modal parameters obtained in a reference state with the modal parameters of a potentially damaged state. This works when a potential damage is causing changes in the normally few modes extracted. However, there might be modes that are affected by a damage, but not easy to extract. The Statistical Subspace-based Damage Detection feature tries to overcome this potential shortcoming of the explicit modal analysis. The major benefits of the new feature are:
- No modal parameter estimation necessary.
- The full dynamic system is compared implicitly instead of comparing a few modes.
- Robust estimation in case of differences in vibration level from measurement to measurement.
- Easy comparison - Simply upload a measurement file and get the damage index without further interaction.
- Can integrate with existing monitoring systems or operated using the well-known ARTeMIS Modal user interface.
The Statistical Subspace-based Damage Detection procedure consists of the following steps:
1. Upload a set of measurement files acquired in a reference "undamaged" state of the structure.
2. Estimate a Reference State Model as an average of the dynamic behavior of the uploaded measurement files.
3. Test all individual measurement files of the reference state with the Reference State Model using Chi-Square testing. The outcome is a single Chi-Square value per measurement file. Use these values to establish an empirical Threshold for Chi-Square values being inside the undamaged Safe Zone.
4. Upload measurement files of the potentially damaged structure and test against the Reference State Model using Chi-Square testing. If the estimated Chi-Square values exceed the threshold, it indicates a significant change of the dynamics of the structure being measured, and as such a potential damage.
In the case of the S101 bridge, a Reference State Model was constructed using the first 100 measurement files. These were acquired on the first day before the damaging process started. All 689 files were then uploaded one by one and tested against the Reference State Model.
Below, the results are presented in a bar diagram where all green bars represent measurements having Chi-Square values inside the threshold (Safe Zone) - the horizontal red line. The measurements used to establish the Reference State Model are highlighted with a gray background to the left of the diagram. When Chi-Square values exceed the threshold, the bars are colored red (Unsafe Zone). The start of the 11 progressive damage scenarios is also indicated with annotations in the top of the diagram.
As it appears from the diagram, the indicator reacts dramatically when the first damage is being introduced at the measurement (Session) indicated with the annotation A.
New ARTeMIS Feature - Analysis Session
In order to host multiple measurements of the same structure for Structural Health Monitoring a new feature called Analysis Session is introduced in ARTeMIS Modal Pro 3.0. In the present case study there are 689 measurement records, and each of these describes a state of the structure. In order to be able to save modes, and other results depending on the specific measurement, these results are saved in a specific Analysis Session. Earlier, separate project files had to be saved, but with the introduction of Analysis Session, all the analyses of the different measurement records can be kept in a single project.
It has been made very easy to define an Analysis Session. If a measurement file is uploaded in the Manage Measurements Task for a specific Test Setup, then a dialog asks if the uploaded data should be uploaded to a new Analysis Session or the current one. The switch between Analysis Sessions is made in the same task.
The Analysis Session feature will be available in ARTeMIS Modal Pro through the new Structural Health Monitoring plug-in.
New ARTeMIS Feature - Analysis History
Having the results of all measurement records in a single project makes it much easier to present the historical development of the dynamic behavior of a structure being monitored. As part of the new Structural Health Monitoring plug-in, an Analysis History Task is introduced, see the above picture. The primary purpose of this task is to display results as a function of the Analysis Session.
Specifically for this case study, the Analysis History Task is used to present a Damage Indicator as a function of the 689 measurement records, each stored in an Analysis Session.
Next ARTeMIS User Training Course, 27-28 February 2014
On 7-8 October 2013, we
organized the ARTeMIS User Training Course for 15 participants worldwide. The course took place at our location in Denmark and was
conducted by our CEO, Palle Andersen.
Statements from our participants:
“The course gave me
all I need to work with the software and to learn by myself.”