PSI - Issue 68

549 3

Koji Uenishi et al. / Procedia Structural Integrity 68 (2025) 547–553 Uenishi et al. / Structural Integrity Procedia 00 (2025) 000–000

a

b

Blast holes

Empty dummy

Screw hole

Screw hole

Blast holes

Empty dummy

100 mm

Desired horizontal exposure of the

200 mm

c

Desired horizontal exposure of the

d

Undamaged

Undamaged

1,500 mm

Fig. 1. Horizontal cutoff of the specific sections of a reinforced concrete (RC) slab by electric discharge impulses (EDI)-induced waves. The dimensions of the slab are 2,500 mm ´ 1,500 mm ´ 300 mm. The diameter of the reinforcing steel bars (rebars) inside the slab is either 13 or 16 mm. (a) In a preliminary experiment, in addition to three blast holes (diameter 18 mm, depth 173.5 mm), four empty dummy holes (diameter 18 mm, depth 300 mm) are set. (b) After the application of EDI from the three blast holes, it is found that due to the horizontal “virtual interface” effect induced by the topmost rebars in the slab, the top surface has been dynamically “sliced” around the blast, empty dummy and screw holes and the rebars in the “sliced” section have emerged. (c, d) After similarly applying EDI to other sections of the slab, the topmost and bottommost rebars have emerged along the center line of the slab while other parts remain undamaged (modified after Uenishi et al. (2024)). 3. Vertical cutoff 3.1. Field observations In the previous chapter, we have seen that a RC slab can be horizontally “sliced” or cut off dynamically by EDI induced waves with some appropriate geometrical setting of blast holes, empty dummy holes and rebars. Here, we show that a RC structure can be dynamically cut off in the vertical direction even more simply without placing empty dummy holes. Figure 2(a) indicates a typical RC block prepared for the vertical cutoff using EDI. The cartridges indicated in red in the blast holes contain the self-reactive liquid and are covered by a stemming material as before. The photographs of the RC block before and after the application of EDI, Fig. 2(b)-(d), clearly indicate that the foremost rebars serve as a vertical virtual interface to concentrate the wave energy only into the region in front of the virtual interface and fragment the concrete in that region. Thus, the concept of a virtual interface can be applied not only to the horizontal partial disintegration (see Fig. 1) but also to the vertical one. Note that, like in Fig. 2(e), we can repeatedly observe this vertical cutoff in the field, showing very good reproducibility of the “virtual interface” effect.