PSI - Issue 46

Koji Uenishi et al. / Procedia Structural Integrity 46 (2023) 136–142

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Koji Uenishi et al. / Structural Integrity Procedia 00 (2019) 000–000

containing the heads of the stud dowels and another (initially virtual) horizontal one near the cartridges (indicated by pink lines), and again, the experimental observation can be properly explained. Note that more brittle concrete can be much more easily fragmented than the steel girder and stud dowels as a matter of course. The crucial mechanical role of virtual planes containing pre-existing planes of weakness and inhomogeneities, like interfaces between concrete material and reinforcing steel bars, has been pointed out by Uenishi et al. (2016) during the investigation of controlled dynamic disintegration of reinforced concrete blocks. Also in this study, the importance of the existence of virtual planes in the dynamic control of fracture development is recognized. When the horizontal distance between each neighboring stud dowel  L is sufficiently small as in the case of the specimen B (Fig. 3(b)), a virtual interface connecting the heads of the stud dowels does exist and the tensile waves reflected at and propagated from the top free surface will be reflected at this virtual interface. Therefore, it will be difficult for the tensile waves to enter the inside of the group of the stud dowels below the virtual interface. On the contrary, if the distance  L is in a relatively large range, like in the specimen A (Fig. 3(a)), the heads of the stud dowels cannot function as a virtual interface, and the tensile waves traveling from the top free surface can move more deeply in the specimen along and between the stud dowels. Similar discussion holds for the wave reflection from the bottom of each specimen. 4. Conclusions Our experimental observations, together with the three-dimensional finite difference simulations, have clearly indicated that also in steel-concrete composite structures, the dynamic evolution of waves and fracture and final pattern of structural disintegration induced by electric discharge impulses (EDIs) are dependent very delicately on the geometrical and loading settings. Especially, in this study, the horizontal distance  L between the stud dowels seems to have played a crucial part. In the specimen B where the horizontal distance is relatively small (  L = 100 mm), the plane virtually formed by the (heads of) stud dowels, for instance, is expected to serve as an interface that prevents the transmission of tensile waves and dynamic cracks are generated on this (initially virtual) horizontal plane. On the other hand, if the distance between the stud dowels is increased, the function of the (heads of) stud dowels as a virtual interface is lost and tensile waves can travel more freely in the specimen. Thus, in the specimen A with  L = 200 mm, larger cup-shaped fractures are induced. The physics-based blast design technique proposed here for controlled dynamic disintegration is applicable not only to the modern cases using EDIs but also to the conventional ones, blasting by explosives. References Andres, U., 1989. Parameters of Disintegration of Rock by Electrical Pulses. Powder Technology, 58, 265–269. Bluhm, H., Frey, W., Giese, H., Hoppe, P., Schultheiss, C., Straessner, R., 2000. Application of Pulsed HV Discharges to Material Fragmentation and Recycling. IEEE Transactions on Dielectrics and Electrical Insulation, 7, 625–636. Hofmann, J., Weiss, Th. G. G., 1997. Pulsed Power Technologies for Commercial Material Reduction and Crushing Applications. 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