PSI - Issue 5

Igor Shardakov et al. / Procedia Structural Integrity 5 (2017) 210–216 Igor Shardakov / Structural Integrity Procedia 00 (2017) 000 – 000

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In order to evaluate the credibility of the proposed technique, we have developed the following experimental procedure. Two accelerometers ( D1 and D2) are located on surface of the reinforced concrete beam at a distance l from the crack. Being installed on the opposite edges of the crack, these sensors are able to record the acceleration vector component normal to the beam surface. The detector D3 is mounted on a striker which hits the beam surface (the point of impact is shown by the red arrow). When passing through the crack, the shock wave front changes. One of the main varying parameters is the absolute maximum value of the amplitude of the first half wave of acceleration. As a criterion for determining the degree of distortion in the acceleration wave passing through the cracked region, we have taken the ratio of amplitudes of the first half waves of the acceleration front recorded in the zones located on the both edges of the crack. Thus we have 2 1 / K A A  (1) where А 1 and А 2 are the maximum amplitudes of the first acceleration half wave (on wave front) obtained at the location points of first and second detectors, respectively. The ratio of amplitudes of the first half wave of accelerations on the beam surface in front and behind the crack can serve as a criterion for assessing the crack opening value and the degree of filling the crack space with the injected material. This criterion has two advantages. First of all, it is just the first half wave amplitude, which is not distorted by the signals reflected and re-reflected from the surfaces of beam fixation areas. Furthermore, the criterion value is independent of the impulse loading value (if the wave process is described reasonably well in the framework of the linear theory of elasticity). In order to provide an experimental and theoretical justification for the approach developed here, we have performed the following cycle of investigations. At the first stage, attention was paid to a study of the passage a shock wave in a beam free of cracks. The reinforced beam, represented schematically in Fig.1, was considered under impact produced by a striker provided with an accelerometer D3. With this device, one can estimate impact loads when analyzing the value of acceleration on the beam surface at the point of impact. The time-dependent acceleration obtained experimentally at this point is presented in Fig.2. The analysis of the obtained data yielded the characteristic time of impact T produced by the striker against the beam surface and the shape of the applied impulse. Based on these parameters, we have obtained the normal force of the striker interaction with the beam surface over the course of time. 3. Mathematical model verification

Fig.2 Changes in accelerations at the point of impact

Impact loading applied to the reinforced concrete beam without a crack was modeled using the linear theory of elasticity. The constructed 3D models allowed us to take into account the interaction of concrete with the iron reinforcement. The boundary-value problem was solved by a finite-element method with ANSYS.