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Civil-Comp Proceedings
ISSN 1759-3433
CCP: 99
PROCEEDINGS OF THE ELEVENTH INTERNATIONAL CONFERENCE ON COMPUTATIONAL STRUCTURES TECHNOLOGY
Edited by: B.H.V. Topping
Paper 186

Simulation of a Crack Detection Method for Concrete Structures using SH Waves

L. Godinho1,4, D. Dias-da-Costa2,4, E. Júlio3,5 and P. Areias3,6

1CICC, Coimbra, Portugal
2INESC Coimbra, Portugal
3ICIST, Lisboa, Portugal
4Department of Civil Engineering, University of Coimbra, Portugal
5Department of Civil Engineering, Instituto Superior Técnico, Technical University of Lisbon, Portugal
6Physics Department, University of Évora, Portugal

Full Bibliographic Reference for this paper
L. Godinho, D. Dias-da-Costa, E. Júlio, P. Areias, "Simulation of a Crack Detection Method for Concrete Structures using SH Waves", in B.H.V. Topping, (Editor), "Proceedings of the Eleventh International Conference on Computational Structures Technology", Civil-Comp Press, Stirlingshire, UK, Paper 186, 2012. doi:10.4203/ccp.99.186
Keywords: wave propagation, non-destructive testing, embedded elements, strong discontinuities, frequency domain, meshless.

Summary
This paper addresses the development of a strategy, based on the propagation of SH waves, for early damage detection of a structure. For that purpose a numerical approach has been selected which combines two distinct algorithms to perform a close to reality simulation of the: i) process of crack propagation; and ii) the propagation of ultrasonic waves in the progressively damaged structure.

The process of crack formation is modelled with a strong embedded discrete crack approach using enriched finite elements [1]. This variationally consistent formulation has been selected due to: i) the possibility of introducing a discontinuity into the finite element mesh irrespective to the boundaries of the enriched finite element; ii) having the additional degrees of freedom placed at the discontinuity and therefore strictly related to the damage of the structure; iii) the possibility of adequately simulating the kinematics of the crack, including both rigid body motion and stretching opening modes; and, more importantly, iv) being a conforming finite element approach which allows the edge to be maintained as fully compatible with the remaining finite element mesh.

To analyse the propagation of SH waves, a boundary element model with domain decomposition is used. In this model, the boundaries of the propagation domain are discretised and the medium is separated in two subregions, in order to avoid numerical problems along the cracked interface. Computational efficiency is achieved by using an iterative strategy for performing the coupling of the subdomains (based on the works of Soares et al. [2]) which leads to smaller matrices describing the behaviour of each subregion.

Application to a test case concluded that the crack propagation model provided reliable results, accurately predicting the evolution of the crack within the structure. With respect to the crack identification by means of SH wave propagation patterns, the results presented permiteed a comparision of the effect of cracks with different lengths, helping in the identification of the relevant differences in the time signals registered at receiver points located on the surface of the structure.

References
1
D. Dias-da-Costa, J. Alfaiate, L.J. Sluys, E. Júlio, "Towards a generalization of a discrete strong discontinuity approach", Computer Methods in Applied Mechanics and Engineering, 198, 3670-3681, 2009. doi:10.1016/j.cma.2009.07.013
2
D. Soares Jr, L. Godinho, A. Pereira, C. Dors, "Frequency-domain analysis of acoustic wave propagation in heterogeneous media considering iterative coupling procedures between the Method of Fundamental Solutions and the Kansa's Method", International Journal of Numerical Methods in Engineering, 89(7), 914-938, 2012. doi:10.1002/nme.3274

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