This paper discusses the influence of environmental factors and of normal material aging on the eigenfrequencies of concrete bridges based on monitoring data registered during 4 years of a specific bridge. It is a new composite steel-concrete bridge built in 2006 in Luxembourg. The measurements are analyzed and compared to literature data. The final objective is the use of real monitored eigenfrequencies for structural health monitoring and damage detection based on identification of stiffness losses in practical applications. Therefore, it is very important to identify and compensate for outdoor influences namely temperature, excitation force level and normal aging effects, like creep and shrinkage of concrete and their impact on material properties. The present paper aims at describing these effects in order to separate them from damage effects. It is shown that temperature change rates and temperature gradients within the bridge have an influence on the eigenfrequencies. Hence the key idea for assessment from the full database is to select only measurements with small temperature differences and slow temperature change rates.
References
[1]
Kullaa, J. (2003) Damage Detection of the Z24 Bridge Using Control Charts. Mechanical Systems and Signal Processing, 17, 163-170.
https://doi.org/10.1006/mssp.2002.1555
[2]
Yan, A.M., Kerschen, G., De Boe, P. and Golinval, J.-C. (2005) Structural Damage Diagnosis under Varying Environmental Conditions—Part I, II. Mechanical Systems and Signal Processing, 19, 847-880.
https://doi.org/10.1016/j.ymssp.2004.12.002
[3]
Magalhaes, F., Cunha, A. and Caetano, E. (2012) Vibration Based Structural Health Monitoring of an Arch Bridge: From Automated OMA to Damage Detection. Mechanical Systems and Signal Processing, 28, 212-228.
https://doi.org/10.1016/j.ymssp.2011.06.011
[4]
Magalhães, F., Cunha, á. and Caetano, E. (2014) Five Years of Continuous Dynamic Monitoring of Infante D. Henrique Bridge. Proceedings of the 9th International Conference on Structural Dynamics, Eurodyn 2014, Porto, 30 June-2 July 2014, 2263-2270.
[5]
Peeters, B. and De Roeck, G. (2000) One Year Monitoring of the Z24-Bridge: Environmental Influences Versus Damage Events. Proceedings of the 18th International Modal Analysis Conference, San Antonio, 7-10 February 2000, 1570-1576.
[6]
Lloyd, G.M., Wang, M.L. and Wang, X. (2004) Thermomechanical Analysis of Long-Term Global Modal and Local Deformation Measurement of the Kishwaukee Bridge Using the Bootstrap. Earthquake Engineering and Engineering Vibration, 3, 107-115. https://doi.org/10.1007/BF02668856
[7]
Gomez, H.C., Fanning, P., Feng, M.Q. and Lee, S. (2011) Testing and Long-Term Monitoring of a Curved Concrete Box Girder Bridge. Engineering Structures, 33, 2861-2869. https://doi.org/10.1016/j.engstruct.2011.05.026
[8]
Soyoz, S. (2008) Long-Term Monitoring and Identification of Bridge Structural Parameters. Computer-Aided Civil and Infrastructure Engineering, 24, 82-92.
https://doi.org/10.1111/j.1467-8667.2008.00572.x
[9]
Zabel, V., Brehm, M. and Nikulla, S. (2010) The Influence of Temperature Varying Material Parameters on the Dynamic Behavior of Short Span Railway Bridges. Proceedings of the 24th International Conference on Noise and Vibration Engineering, Leuven, 20-22 September 2010, 1519-1530.
[10]
Moaveni, B. and Behmanesh, I. (2012) Effects of Changing Ambient Temperature on Finite Element Model Updating of the Dowling Hall Footbridge. Journal of Engineering Structures, 43, 58-68. https://doi.org/10.1016/j.engstruct.2012.05.009
[11]
Pirner, M., Fischer, O. and Urushadze, S. (2009) Long-Term Observation of Old RC Structures Using Dynamic Response. Proceedings of the IMAC-XXVII, 9-12 February 2009, Orlando.
https://sem.org/wp-content/uploads/2015/12/sem.org-IMAC-XXVII-Conf-s38p003 -Long-term-Observation-Old-RC-Structures-Using-Dynamic-Response.pdf
[12]
Au Francis, T.K. and Si, X.T. (2012) Time-Dependent Effects on Dynamic Properties of Cable-Stayed Bridges. Structural Engineering and Mechanics, 41, 139-155.
https://doi.org/10.12989/sem.2012.41.1.139
[13]
Bungard, V. (2011) Condition Assessment of Concrete Structures and Bridges Using Vibration Monitoring in Comparison to Changes in Their Static Properties. PhD Dissertation, University of Luxembourg, Shaker Verlag GmbH, Luxembourg City. https://www.amazon.de/assessment-structures-monitoring-comparison -properties/dp/3844000771
[14]
van Overschee, P. and de Moor, B. (1996) Subspace Identification for Linear Systems: Theory, Implementation, Applications. Kluwer Academic Publishers, New York City. https://doi.org/10.1007/978-1-4613-0465-4
[15]
Mahowald, J. (2013) Evaluation of Dynamic Damage Indicators on Real-Life Civil Engineering Structures: Measurement Uncertainty and Environmental Influences Considered. PhD Dissertation, University of Luxembourg, Shaker Verlag GmbH, Luxembourg City.
[16]
Moser, P. and Moaveni, B. (2011) Environmental Effects on the Identified Natural Frequencies of the Dowling Hall Footbridge. Mechanical Systems and Signal Processing, 25, 2336-2357. https://doi.org/10.1016/j.ymssp.2011.03.005
[17]
Mahowald, J., Maas, S., Nguyen, V.H., Waldmann, D. and Zuerbes, A. (2014) Some Conclusions from the Measurements of Temperatures and Their Gradients on Eigenfrequencies of Bridges. Proceedings of the 9th International Conference on Structural Dynamics, Eurodyn, Porto, 30 June-2 July 2014, 2319-2323.
[18]
Maas, S., Zürbes, A., Waldmann, D., Waltering, M., Bungard, V. and De Roeck, G. (2012) Damage Assessment of Concrete Structures through Dynamic Testing Methods, Part 2, Bridge Tests. Engineering Structures, 34, 483-494.
https://doi.org/10.1016/j.engstruct.2011.09.018
