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1) According to the SMS records due to traffic effects, the maximum values of positive strain on the
webs of SB2-N16 and SB2-S16 are close to the maximum strain (24 microstrain) in the load test of
2000. Moreover, the monthly maximum crack opening displacements have exceeded the maximum
value (0.002 in) measured in the load test since December 2001. Although the flexural stiffness of the
bridge is still unchanged, some measures should be taken to control the growth of shear cracks on the
web within a reasonable limit. It is recommended to impose a restriction to the speed and weight of
trucks going across the bridge. An automated camera system could be added in our Structural
Monitoring System to photograph any vehicle surpassing the threshold of speed or weight that would
cause harm to the bridge.
2} ) Temperature change has a significant effect on the change of strain and crack opening
displacement. Based on the records of Structural Monitoring System, the maximum change of strain
due to temperature effect is from - 40.8 to 43.7. The corresponding temperature change is 18 °C. So
the average change of strain is about 5 microstrain with the temperature change of 1 °C. Similarly, the
change of crack opening displacement is about 0.0005 in for every temperature change of 1°C.
3) The dynamic properties are almost the same as the results measured in 2000. The modal frequencies
of this bridge seem to have stayed relatively constant over these years.
4) The advanced monitoring system can automatically pick up and analyze the data and transfer the
processed data from the bridge through a specified telephone line. It can count the number of trucks,
calculate their speed and record the exact time upon which they pass the sensor location. It's quite
useful for monitoring the traffic on the bridge in real time. Using this system as a basis, the next step
will be to build a new traffic warning system. By embedding a decision-making system in the sensory
system, this new system will be able to automatically react to the strain or acceleration signal
exceeding the predefined threshold. For example, in the case of a heavy traffic jam or any severe
accident happening on the bridge, it can send an on-line warning to the Department of Transportation
immediately.
References
1. D. J. Ewins, (1985) Modal Testing: Theory and Practice, John Wiley, New York.
2. R. Shepherd and A. W. Charleson, (1971) "Experimental Determination of the dynamic Properties
of a Bridge Substructure", Bulletin of the Seismological Society of America, 61,1529-1548.
3. R. Kohoutek, (1993) "Tests on Bridge over Talbragar River at Dubbo", Proceedings of the 11 th
International Modal Analysis Conference, Kissimmee, FL., 1168-1174.
4. P. K. Lee, D. Ho and H. W. Chung, (1987) "Static and Dynamic Tests of concrete Bridge", ASCE
Journal of Structural Engineering, 113, 61-73.
5. C.R. Farrar, W. E. Baker and T .M. Bell, (June 1994) "Dynamic Characterization and Damage
Detection in the 1-40 Bridge over Rio Grande", Research report Los Alamos National Laboratory,
LA-12767-MS.
6. Wang, M. L, F. Xu, and George M. Lloyd, (July 2000) Results and Implications of the Damage
Index Method Applied to a Multi-Span Continuous Segmental Prestressed Concrete Bridge,
International Journal of Structural Engineering and Mechanics, Vol. 10, No. 1, 37-52.
7. Wang M. L., and D. Satpathi, (Sept. 1997) Damage Detection of a Model Bridge Using Modal
Testing, Structural Health Monitoring—Current Status and Perspective, Technomic Publishing Co.
Edited by F. K. Chang, pp. 589-602.
8. Wang, MX., F. Xu and G. Lloyd, (Aug. 2000) Health Assessment of a Post-tensioned Concrete
Bridge, In proceedings of ASCE's 2000 Structure Congress, Philadelphia, PA.