Genadii Farenyuk, Iurii Kaliukh 2018 JOINT MEETING FIB&SE RIBK EXPERIMENTAL AND THEORETICAL DIAGNOSTICS OF DEFECTS IN FERROCONCRETE PILES BASED ON REFLECTION OF LONGITUDINAL AND TRANSVERSE WAVES Author/s Genadii Farenyuk, Iurii Kaliukh Name of Presenter, Job Title / Affiliation Iurii Kaliukh, Deputy Manager of Department, Research Institute of Building Constructions, Kiev, Ukraine, 2018

DEFECTS IN PILES

DEFECTS IN PILES

Overview Introduction Existing model New model Mathematical modeling of the pile with a neck Conclusion

1. Introduction. Problem Statement. Ferroconcrete piles, unlike other reinforced concrete structures, have several peculiarities. Firstly, an access to the ferroconcrete pile installed into the soil is limited to one free end and a lateral surface, the total area of which usually does not exceed 12% of the total area of the pile surface. Secondly, some specific defects occur during the ferroconcrete pile insertion into the soil. Thirdly, the concrete mixture hardening in the pile vertical position leads to an uneven effect of pile dead weight along a pile length. As a result, the structural irregularity is possible, when the physical and mechanical properties of concrete along the pile length may considerably vary

1. Introduction. Problem Statement. Fig.1 Functional scheme of pulsed echo-method with shock excitation of compression wave: 1 - explored pile; 2 - defect; 3 - receiver of acoustic oscillations; 4 - shock emitter of elastic waves; 5 - a buffer of information; 6 - recorder; 7 - elastic wave; 8 - probing impulse; 9 - moon impulse from the defect; 10 - moon impulse from the opposite end of the pile.

1. Introduction. Problem Statement. 1.The stress wave excited by an impact on the surface spreads along the internal structure and shocked surface of the object under test. 2. The surface displacements resulting from the reflections of these waves are recorded by a transducer (accelerometer) located near the point of impact. 3.The recorded values of time displacements are transformed into a graph of amplitude versus frequency. 4. The repeated reflections of the stress wave from the impacted surface, defects and/or other external surfaces cause the increase of the number of resonance frequencies that can be identified by a spectrum and used for the assessment of the structure continuity or for the defect localization.

2. Existing mathematical models All existing to date models for the control of ferroconcrete piles installed in the soil are based on the versions of a theoretical model using only longitudinal vibrations: 1. Model not taking into account a viscous component ТКS–1 device, SE NDIBK (Operation manual 2004): 2. Maxwell model, КSDK–3.3 device, Kyiv National University of Construction and Architecture 3. Voigt-Kelvin model (is used in the works of the most researchers in the field of piles diagnostics including (e.g., Liao et al. 1997, Kim et al. 2002, Kim et al. 2006, Ambrosini et al. 2005) and others

2. Existing mathematical models Kim in his works (e.g., Kim et al. 2002, Kim et al. 2006) compared the numerical and experimental investigations of the possibilities of the impact-echo method applications for flaw detection by means of the customized models of piles with circular cross-sections. The models of bars with artificial defects: a) axisymmetric voids, b) non-axisymmetric voids, c) necks and d) bulges

2. Existing mathematical models The theoretical model of wave processes used by Liao, Ambrosini and Kim was the same. But it was not capable of meeting all requirements as to the pile control including the small sized defects identification, defect type determination and pile geometry. This fact was not strange from the point of view that all described models applied the formulae of the propagation of only longitudinal vibrations. The longitudinal vibrations allowed to obtain the characteristics of piles along their lengths, namely the pile lengths and defects locations.

3. New mathematical model We consider the ferroconcrete pile as an flexible cable (Kaliukh 1993). where E is an unit matrix

4. Mathematical modeling of the pile with a neck Fig. 2. The initial results of the defect-free pile mathematical modeling: a) shear vibrations speed and its spectrum, b) bending vibrations speed and its spectrum.

4. Mathematical modeling of the pile with a neck Fig. 3. The initial results of mathematical modeling of the pile with a neck size of 50% at a depth of 7 m: a) shear vibrations speed and its spectrum, b) bending vibrations speed and its spectrum.

CONCLUSION Based on the analysis of production needs and the state of the problem development, the necessity of creating a pile generalized model, which would allow obtaining the more plausible theoretical signalograms of wave processes in ferroconcrete piles in the soil. A few numerical models of the wave process signalograms were developed based on the finite element method and finite difference method that take into account the various types of oscillatory processes in ferroconcrete piles in the soil with respect to the types and locations of defects, soil conditions of the construction project, nature and type of sounding actions and transducer location coordinates.

CONCLUSION 3. Summarizing the performed analysis, it is possible to draw a conclusion that as of today the optimal technology for the control of ferroconcrete piles arranged in the soil is based on the low-frequency pulse wave excitation followed by the recording of the timing characteristics of its propagation by transducers mounted on the surface of the pile. 4. It is difficult to clearly answer, which of the methods is optimal: e.g., Liao et al. 1997, Kim et al. 2002, Ambrosini et al. The problem, obviously, is not the choice of a pulse excitation method, but the further interpretation of a recorded signal. As it was noted above, the theoretically justified criteria are necessary for the identification and classification of defects in piles.

Thanks for your attention! Acknowledgement Results presented herein have been obtained with the financial support from the State Enterprise “Research Institute of Building Constructions”. These supports are gratefully acknowledged. Our special thanks are extended to our colleagues Prof., Doctor of Eng., Nikalay Marienkov, Ph.D. Vitaliy Gluhoskii for their support in the site and cabinet work. Thanks for your attention!