LSV-CoMaND project

Laser Scanning Vibrometry in Concrete and Masonry Non Destructive testing (LSV-CoMaND) is a research project which deals with the development of an analytical protocol and data post-processing methodology, for the non-contact and non-destructive detection of structural flaws in concrete and masonry constructional elements, exploiting Laser Scanning Vibrometry (LSV). Project full name is Development of methodology for damage diagnosis and flaw mapping in concrete and masonry structures employing Laser Scanning Vibrometry (LSV)”. Vibration based nondestructive control of structural integrity relies on the determination and evaluation of structures’ dynamic features. As dynamic features are termed parameters like resonant frequencies and related amplitudes which modulate the vibration patterns a construction emerges when is forced to dynamic motion by external dynamic loading (e.g. Earthquake, Impact, Impulse excitation etc). In present case dynamic characteristics are identified by the post-processing of vibration velocity signals that acquired employing a PSV–500H vibrometer (Fig.1). PSV-500H is part of equipment of Technical University of Crete’s Applied MEchanics Lab (AMEL) and has been supplied by Polytec Gmbh.

comand_liarakos_fig1

Fig. 1 PSV-500H and Laser Scanning Vibrometry in masonry and concrete members’ NDT.

Laser Scanning Vibrometer (LSV) is able to measure remotely and contactless vibration velocity of constructions surface points in direction of incident Laser beam. The physical principle behind LSV is Laser Doppler Effect (LDE). Vibration velocity can be acquired either on a single control point or on a multi-point monitoring grid allowing a spatially illustration of constructions vibration modes (Liarakos, 2015). LSV technique and PSV-500H laser vibrometer are widespread in scientific domain of metallic structural system dynamic response measuring. Several applications have been signed in international literature concerning scanning of vibration velocity of metallic machine elements, metallic structural elements (beams, columns etc), metallic planar bodies (e.g. car outer shells, wind turbines blades), PCBs etc (Polytec, In Focus). However in experimental mechanics discipline that deals with the monitoring of structures which exhibit high stiffness and strong mechanical energy attenuation (high internal damping), like concrete and masonries, literature is quite restricted. In present project are investigated LSV abilities in vibration based NDT both of lab scale concrete and masonry specimens (Fig. 1), and of large scale historical buildings that are founded in nearby area of Chania region. Vital interest exhibits historical masonry building that already have experienced reviving interventions, especially in case where the restoration is materialized via concrete strengthening elements (e.g. lintels and tie beams, Stavroulaki and Liarakos, 2012).

Fig. 2 LSV based concrete beam vibration pattern evaluation, for different states of flexural test induced tensile crack. Colormaps: Vibration spectral velocity at 500 Hz. AMEL 2017.

Key aims of LSV-CoManD project:

  1. Developing of an integrated analytical protocol for contactless and remote scanning of vibration velocity of concrete and masonry structures, which provides a detailed procedure plan that begins from constructions efficient excitation and completes  with data post-processing and evaluation.
  2. Scripting MatLAB / GNU-Octave or/and  R codes for LSV acquired data post-processing and structures dynamic response identification and modelling (Transfer functions defining and their parameters calculation).
  3. Efficient positioning and mapping of mechanical damages in concrete and masonry elements. Application of mapping techniques that relied on the spatial statistical correlation of LSV-acquired data (e.g. 2D Polynomial Interpolation and Ordinary Kriging) (Fig. 2).

Acknowledgments 

LSV-ComMaND project is funded by Technical University of Crete’s Special Account for Research as postdoctoral research (Oct. 2016 – Sep. 2017).

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