PSI - Issue 5

Martini et al/ Structural Integrity Procedia 00 (2017) 000 – 000

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Rachel Martini et al. / Procedia Structural Integrity 5 (2017) 1108–1115

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2.1. GPR

After the respective construction and curing, a GPR survey was performed (Fig. 1(a)), according to the following methodology: horizontal and vertical linear and parallel profiles were conducted at 5 cm intervals, using GPR antenna center frequencies of 1.6 GHz and 900 MHz. The differences identified in the GPR radargrams (attenuation parameters, wave propagation velocity and dielectric constant of the material) are compared with the results obtained in the sonic tests. Prior to interpretation, the obtained raw radargrams are then processed. Some of the currently used processing steps are the following:  Pre-processing: quality check of radargram;  Set zero time: spatial coherence;  Application of gains;  Background removal: lateral moving average amplitude of the radar to a particular start time window;  Dewow filtering: Fixing baseline with an amplitude equal to zero;  Bandpass filtering;  Migration;  Deconvolution;  Conversion time / depth: velocity analysis - hyperbolic function with estimated adjustment; The sonic tests we conducted using as excitation source an instrumented impact hammer with a hard aluminum tip (Fig. 1 (b)). The generated signals were collected by piezoelectric accelerometers used as receiving sensors in preset positions. The acquisition/recording of the readings was made with a data acquisition board, connected via USB to a laptop computer with software specifically developed in LabVIEW (in LESE) for this type of testing, which allowed the visualization and analysis of results. Agreeing to the conventional standards, three main test configurations are identified. Direct sonic test when the emission and acquisition points are on the opposite sides of the structure; semi direct sonic test if emitter and receiver are located on adjacent walls; indirect sonic test, if emitter and receiver are located on the same side of the wall. Direct and indirect sonic tests were performed on a 35 cm regular grid. Consequently, for the direct sonic tests, 12 readings were obtained, which corresponds to 3 columns with 4 receivers each. For the indirect sonic tests, ISIM, (Miranda 2011), each impact corresponds to three indirect inline tests, one for each receiver and each test is repeated three times. Furthermore, to compare the spatial signals variability, three vertical lines per panel were considered, that is, three ISIM tests were performed per panel, which corresponds to 27 indirect tests per panel. In conclusion, all wall typology (PP1 – PP5) provided 135 indirect tests and 180 direct test. Using the sonic test technique (direct and indirect), assuming the conventional controversial approach, is possible to obtain the wave propagation velocities of P and R. With these velocities is possible to calculate values of Poisson's ratio and the Young's modulus, to characterize the material using equations 1-2: = √ × (1 − ) × (1 + ) × (1 − 2 ) (1) = 0,87 + 1,12 × 1 + × √ × 2 × (1 + ) (2) 2.2. Sonic test