PSI - Issue 64

Hideki Oshita et al. / Procedia Structural Integrity 64 (2024) 48–55 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

51

4

200mm

concrete

concrete Round bar diameter:16

Spiral coil Planer coil

Round bar diameter:16

50mm

Circular spiral coil

Planar coil

200mm

Rectangular spiral coil

20mm

Round bar diameter:16

180mm

slab

column

concrete

beam

rebars

Fig. 3. Shape of Coils

Fig. 4. (a) Circular spiral coil(Column); (b) Rectangular spiral coil(Beam); (c) Planar coil(slab)

(a) Coil Shapes Both spiral coils and planar coils have the dimensions shown in Fig.4, and they use copper wire with a diameter of 2 mm. Let me explain the details of each type of coil based on the figure: Circular spiral Coil : The copper wire is wound in a circular shape with 20 turns, spaced 10 mm apart along the axial direction of the reinforcing bar. The outer diameter of the circular helical coil is 103 mm, and its height is 200 mm. Rectangular spiral Coil : The copper wire is wound in a square shape with 20 turns, spaced 10 mm apart along the axial direction of the reinforcing bar. Each side of the rectangular helical coil has a length of 103 mm, and its height is 200 mm. Planar Coil : The copper wire is wound within a plane in a square shape with 18 turns, spaced 10 mm apart. Each side of the planar coil has a length of 360 mm. (b) Analysis Overview In RC structures, irregular-shaped reinforcing bars are commonly used. However, the difference in induced current density between irregular-shaped reinforcing bars and standard round reinforcing bar surfaces is minimal. Therefore, for this analysis, we will use round reinforcing bars. The details of the analysis model is that a circular coil with an inner surface of φ100×200 mm and four reinforcing bars, each 200 mm in length, are placed at 90° intervals along the axial direction of the coil. The analysis parameters include current value and frequency, set to 1A and 10Hz, respectively. Additionally, the conductivity of the reinforcing bars is set to 3.4 × 10 5 S/m based on measurements, and the relative permeability is set to 2000. (c) Analytical Evaluation of Spiral Coils The induced current density on the reinforcing bar surface is depicted in Fig.5. In all analysis models, the induced current density forms a closed loop in the circumferential direction, with the highest values at the reinforcing bar surface and gradually decreasing toward the interior of the cross-section. Along the axial direction of the reinforcing bars, regardless of the coil shape, the central region of the coil (approximately 120 mm) exhibits high and nearly uniform induced current density. However, at the upper and lower ends of the coil (approximately 40 mm), there is a sharp decrease. This phenomenon is influenced by the coil’s boundary conditions. If we consider induced current as the primary factor affecting corrosion prevention, the central region appears to be the most effective. Regarding the impact of coil shape on the maximum induced current density, the maximum induced current density is 0.399 kA/m². From the analytical study regarding the influence of coil shape on the direction and density distribution of induced currents on the reinforcing bar surface mentioned above, if we assume that the primary factor for corrosion prevention is induced current, then helical coils are likely more effective than planar coils. Therefore, in the subsequent sections, we will investigate the corrosion prevention effect using experimental and analytical methods based on circular helical coils.