Research

Project Number:
03-17

Research Project:
Innovative Bridge Structural Health Monitoring Using Veriable Stiffness and Damping Devices

P.I. Name & Address:
Erik A. Johnson
Department of Civil and Environmental Engineering
University of Southern California
Los Angeles, CA 90089-2531
Tel:(213) 740-0610
Fax:(213) 744-1426
Email: johnsone@usc.edu

Project Objective:
In addition to the long-term degradation and acute damage from earthquakes and other natural hazards that pose a danger to the aging infrastructure in today's urban environment, our nation faces new uncertainties and, therefore, new priorities to confront the concerns of global terrorism. Many of the threats of terrorism have been directed towards major structural lifelines as well as other types of structures. Further, this is a time when many public budgets, such as that of the State of California, are well in the red, demanding increased fiscal productivity. Currently, monitoring the health of most structures is dominated by manual, visual inspection - a time-intensive and costly procedure that does not allow for rapid and quantitative condition assessment of a structure. Determination of the integrity of bridges in the aftermath of a serious earthquake, terrorist act, or other disaster will dictate effective prioritization of post-disaster actions, such as routing emergency crews to affected areas and the rerouting of emergency vehicles and the general public to safe lifelines through the city.

Some autonomous structural health monitoring and damage detection methods based on ambient vibration have been considered for civil structures. Accurate characterization of the health of a structure necessitates precise knowledge of localized damage with the structure. However, current structural monitoring methods that use global structural vibration methods are largely ineffective for detecting localized damage. The methods that can provide localized information require a cost-prohibitive number of sensors distributed throughout the structure.

The investigator has recently shown that there is significant potential in an alternate approach by providing parametric changes to a structure's stiffness and damping characteristics. Such an approach is not possible in a conventional structure, but can be achieved using variable stiffness and damping devices (VSDDs). Similar to conventional passive damping devices that have already been installed in bridges for reducing structural vibration caused by seismic motion and wind, VSDDs are a new technology that shows promise for improving the performance of structures subjected to natural hazards. In addition to providing near optimal damping strategies for vibration mitigation, these low-power and fail-safe devices can also provide the parametric changes required for health monitoring. In previous studies, estimates of structural stiffness have been made more accurate, compared to a conventional structure, by using one or more VSDDs.

The focus of this project is to develop reliable behaviors of VSDDs to provide improved structural identification of bridges to better capture the state of structural health. The simple VSDD behavior in prior research, such as mimicking discrete stiffness or damping devices, will be extended to forces that vary in time according to both local and global responses. VSDD models will be integrated with more complex dynamic models of bridge motion. Simulation will compute the response of the combined system due to ambient excitation (e.g., wind, microtremor, etc.). Several structural identification methods will be used to process the simulated response to determine dynamic characteristics indicative of damage. By changing the type and actions of the VSDDs, multiple "fingerprints" of the structural response will be obtained. It is expected that the integration of VSDD technology with structural health monitoring will capitalize on their synergies to provide structures that are more reliable, have superior performance, and are less-costly to maintain.

Task Descriptions:
1. Determine optimal time-varying VSDD behavior in analytical study (2 months)
2. Determine sources of large covariances in structural parameter estimates (2 months)
3. Determine VSDD behavior to minimize large estimate covariances (1 month)
4. Develop complex smart-structures-oriented bridge model (1 month)
5. Develop models of ambient excitation for bridge model (2 months)
6. Study efficacy of VSDDs in time-domain structural identification (2 months)
7. Draft of final report submitted to METRANS (1 month)
8. Final report submitted to METRANS (1 month)

Milestones, Dates:
June 1, 2003 - May 31, 2004; final draft report 5/31/04

Total Budget:
$75,000

Student Involvement:
One Student @ 50% time 12 months
One Student @ 25% time 9 months

Relationship to Other Research Projects:
Extends 01-10 project research; part of infrastructure focus area

Technology Transfer Activities:
Project report posted on the website

Potential Benefits of the Project:
Better structure monitoring technology

TRB Keywords:
Highway infrastructure

Primary Subject:
Maintenance and operations

Goals:
Safety, mobility

Enabling Research:
Sensing and measurement

Modal Orientation:
Highway