PSI - Issue 44

Hasan Borke Birgin et al. / Procedia Structural Integrity 44 (2023) 1624–1631 Hasan Borke Birgin et al. / Structural Integrity Procedia 00 (2022) 000–000

1627

4

hammer hits on sensor locations

hammer hits on zones

3200 mm

3200 mm

150 mm

150 mm

1 2 3 4 5

1 2 3

250 mm

250 mm

R k

R k

simple supports

V k V 1

V 2 V 3

V k V s

ch1 ch2 ch3

ch1

sensing circuit

sensing circuit

ch4

ch2

V 0

(a)

(b)

V 0

Fig. 3. Test setups of beams: (a) beam made of smart concrete; (b) beam with embedded smart concrete sensor cubes.

4. Tests and setups The test setups employ a shunt resistor of R k = 100 k Ω connected in series with the beam electrodes or smart sensors. The use of a shunt resistor is necessary for measuring the resistance. The test setups formed for the dynamic tests on simply supported beams are illustrated in Fig. 3. Being connected in series, the constant resistance value of the shunt resistor works as a reference for the evaluation of the instant specific resistance values of the smart sensor. In Fig. 3(a) the setup shows the distributed sensing model for the beam made of smart concrete material. Four channels of the data acquisition system were employed for the data reading, at 1000 Hz. The voltage time histories V 1 , V 2 , V 3 , and V k were read through ch1, ch2, ch3, and ch4, respectively. Employing the first Ohm’s law, the Eq. 1 provides the resistance R i of the i-th segment: R # (t) = R ( V # V (t) ( (t) (1) where subscript “i” denotes the segment number according to Fig. 3(a). The acting loads for this test were hammer hits. Two load schemes were adopted for dynamic tests: (i) the hits were placed consecutively on zones 1, 2, 3, 4, and 5 as indicated in Fig. 3(a), and this hit sequence was repeated four times; (ii) ten hits were performed on the central zone of the beam. The input voltage, V 0 , was fixed at 10 V DC. Similarly, the sensing scheme presented in Fig. 3(b) adopted the above-presented methodology for forming the sensor resistance time history, R s (t). The sensors were connected to the sensing circuit individually, and for this setup, two channels of data acquisition were used for obtaining voltage time histories V s and V k . In this setup, the acting loads were hammer hits placed consecutively on the sensor locations 1, 2, and 3 (Fig. 3(b)). The voltage input, V 0 , for the tests with embedded sensors was 5 V DC. The DC voltage levels selected for the different setups were tailored for the specific test, for enhancing the sensing quality of the signal. The data acquisition system for the dynamic tests was composed of National Instruments devices. The voltage output was sourced by PXIe-4138 and the analog-to-digital converter for voltage reading was PXIe-4302, which was capable of handling data rates up to 5000 Hz. Both devices were mounted on a PXIe-1096 chassis. The voltage sourcing and acquisitions have been programmed using LABVIEW. The post-processing of the obtained data has been performed using MATLAB by employing existing libraries for the continuous wavelet transform for conducting time-frequency analysis.