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Keywords: modal testing, structural damage, natural frequencies, damage detection.

Summary

Since the 1970s research has been conducted in order to detect structural damage from modal testing [1]. This paper gives a coherent explanation to the following question: It is possibly to detect structural damage from stiffness, mass or damping values obtained from modal testing techniques?

Single or multiple degree of freedom structural dynamic behaviour has been reported in many books and publications from the structural designer's point of view, but it is more difficult to find publications about the theoretical background of modal testing [2]. This mathematical theory is employed in order to obtain stiffness, mass and damping properties from dynamic load tests records (displacements, velocities or more frequently accelerations) [3]. In his book Ewins [4] presents a global review of modal testing techniques based on his long experience in this field.

In this paper simple analytical and numerical examples are presented in order to analyze past proposed methodologies and experimental results for detect and identify structural damage.

A historical summary of the publications in this field is presented to identify the main authors, investigation lines, etc., and a graphical qualitative analysis is carried out in order to detect the lack of investigation and mistakes with the aim of preventing future errors.

Two different precast floors specimens are tested in the laboratory under static and dynamic loads. On one of the two specimens failure has been induced to produce transverse shear defects. Static and dynamic properties of two precast floor specimens are obtained by tests. Results of the two elements are compared.

Some conclusions are obtained and the most relevant is the inability of dynamic testing to detect this kind of damage since the excitation level during the dynamic testing is too low to take specimen stresses into the transverse shear failure range. The initial tangent stiffness (which is obtained at a dynamic loading test) is very similar from one specimen to another, the static and dynamic results are very similar in both specimens. Finally some guidelines to obtain satisfactory results are given.

References

1: D.J. Ewins,"Structural Dynamics 2000: Current Status and Future Directions", 2000.
2: R.W. Clough, J. Penzien "Dynamics of Structures", Mcgraw-Hill College, 2 edition, 1993.
3: J.C. Araiza Garaygordóbil, "Dynamic Assesment of Structural Building Components", PhD Thesis, UPC, Barcelona, 2003.
4: D.J. Ewins, "Modal Testing: Theory, Practice and Application", 2001.

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Front Page Browse CCP CSETS CTR IJRT Other Authors Search Purchase Guide FAQ Contact us	Civil-Comp Proceedings ISSN 1759-3433 CCP: 91 PROCEEDINGS OF THE TWELFTH INTERNATIONAL CONFERENCE ON CIVIL, STRUCTURAL AND ENVIRONMENTAL ENGINEERING COMPUTING Edited by: B.H.V. Topping, L.F. Costa Neves and R.C. Barros Paper 75 Structural Damage Assesment aided by Modal Testing S. Ivorra¹, C.M. Gisbert², P.A. Calderón² and F.J. Pallares³ ¹Department of Construction Engineering, Public Works and Urban Organization, University of Alicante, Spain ²Department of Construction Engineering, Universidad Politécnica de Valencia, Spain ³ICITECH, Universidad Politécnica de Valencia, Spain doi:10.4203/ccp.91.75 purchase the full-text of this paper Full Bibliographic Reference for this paper , "Structural Damage Assesment aided by Modal Testing", in B.H.V. Topping, L.F. Costa Neves, R.C. Barros, (Editors), "Proceedings of the Twelfth International Conference on Civil, Structural and Environmental Engineering Computing", Civil-Comp Press, Stirlingshire, UK, Paper 75, 2009. doi:10.4203/ccp.91.75 Keywords: modal testing, structural damage, natural frequencies, damage detection. Summary Since the 1970s research has been conducted in order to detect structural damage from modal testing [1]. This paper gives a coherent explanation to the following question: It is possibly to detect structural damage from stiffness, mass or damping values obtained from modal testing techniques? Single or multiple degree of freedom structural dynamic behaviour has been reported in many books and publications from the structural designer's point of view, but it is more difficult to find publications about the theoretical background of modal testing [2]. This mathematical theory is employed in order to obtain stiffness, mass and damping properties from dynamic load tests records (displacements, velocities or more frequently accelerations) [3]. In his book Ewins [4] presents a global review of modal testing techniques based on his long experience in this field. In this paper simple analytical and numerical examples are presented in order to analyze past proposed methodologies and experimental results for detect and identify structural damage. A historical summary of the publications in this field is presented to identify the main authors, investigation lines, etc., and a graphical qualitative analysis is carried out in order to detect the lack of investigation and mistakes with the aim of preventing future errors. Two different precast floors specimens are tested in the laboratory under static and dynamic loads. On one of the two specimens failure has been induced to produce transverse shear defects. Static and dynamic properties of two precast floor specimens are obtained by tests. Results of the two elements are compared. Some conclusions are obtained and the most relevant is the inability of dynamic testing to detect this kind of damage since the excitation level during the dynamic testing is too low to take specimen stresses into the transverse shear failure range. The initial tangent stiffness (which is obtained at a dynamic loading test) is very similar from one specimen to another, the static and dynamic results are very similar in both specimens. Finally some guidelines to obtain satisfactory results are given. References 1 D.J. Ewins,"Structural Dynamics 2000: Current Status and Future Directions", 2000. 2 R.W. Clough, J. Penzien "Dynamics of Structures", Mcgraw-Hill College, 2 edition, 1993. 3 J.C. Araiza Garaygordóbil, "Dynamic Assesment of Structural Building Components", PhD Thesis, UPC, Barcelona, 2003. 4 D.J. Ewins, "Modal Testing: Theory, Practice and Application", 2001. purchase the full-text of this paper (price £20) go to the previous paper go to the next paper return to the table of contents return to the book description purchase this book (price £140 +P&P)
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