PSI - Issue 13

Koji Uenishi et al. / Procedia Structural Integrity 13 (2018) 652–657 Uenishi et al. / Structural Integrity Procedia 00 (2018) 000 – 000

654

3

a

b

Blast holes

Screw holes for crane carriage

Dummy holes

c

d

e

Blast holes

Dummy holes

Desired rather straight crack

Blast holes

Unnecessarily curved crack

100 mm

Fig. 1. Top and side views of the typical rectangular concrete specimens for the field fracture experiments using electric discharge impulses (EDI), (a) the case IC-09/00 and (b) IC-10/00 [unit: mm]. Blast, empty dummy and screw holes are denoted by red, blue and yellow holes, respectively; (c) This snapshot taken by a normal video camera during the fracture process for the case IC-09/00 (a) suggests that the cracks may first develop due to propagation and interactions of waves induced by EDI, and later widen owing to the effect of gas pressurization with ejection of the stemming material; Top view of the specimens after the dynamic fracture experiments, (d) the case IC-09/00 and (e) IC-10/00. The original grid spacing marked for a reference purpose is 50 mm, and we notice the generation of an unnecessarily curved crack connecting the two blast holes in (d) as well as a desired, rather straight crack that directly connects the three blast holes in (e). We expect to utilize our current method under critical situations of partial destruction of structures made of solid materials in urban areas where no explosives as well as absolutely no damage to the surroundings is allowed and a more sophisticated three-dimensional technical handling is accepted even in practical fracturing operations. Figures 1(d) and (e) show the top view of the final fracture patterns taken after the dynamic experiments. In the case IC-09/00 (Fig. 1(d)), an unnecessarily curved main crack connecting the two blast holes is recognizable. As both sets of a blast and four dummy holes are situated rather close to the free surfaces on the sides, undesired cracks extending from the blast holes to the screw holes through the dummy holes as well as those to the free surfaces on the sides are induced. In the case IC-10/00 (Fig. 1(e)), we immediately find that the main crack path is rather straight as desired, especially in the central part. Near the free surfaces and screw holes on the sides we observe undesired cracks also in this case but their extent looks smaller than the above case IC-09/00. Crack propagation seems to be more stable and more largely governed in the case IC-10/00 than the case IC-09/00, and the geometrical and loading