PSI - Issue 42

6

Koji Uenishi et al. / Procedia Structural Integrity 42 (2022) 755–761 Uenishi et al./ Structural Integrity Procedia 00 (2022) 000–000

760

a

b

Stud dowels

Larger tension

2.0  10 -4

Cartridge

Compression Larger tension

Stemming

 L = 200 mm

Cartridges

Mach fronts

 2.0  10 -4

Reinforcing steel bars

c

 L = 200 mm

Stud dowels

Cartridges

 L = 200 mm

Steel girder

Fig. 4. (a) Typical steel-concrete composite structure where a reinforced concrete slab is placed on top of a steel girder and stud shear connectors (stud dowels) [unit: mm]. (b) Numerically generated contours of volumetric strain in the half part of the specimen at 140  s after the start of simultaneous application of EDI. Mach waves can propagate from bottom to top along the stud dowels, and their fronts can play an important role in the dynamic development of (boundaries of) tensile and compressive regions. The boundaries between the compressive parts and the regions of larger tension above the fracture strength can form the cup-shaped fracture, as illustrated by the black broken lines. (c) The specimen after the simultaneous application of EDI. Cup-shaped fractures linking the cartridges with the heads of the stud dowels, indicated by black lines, have indeed emerged (modified after Uenishi et al. (2022)). 4(c)). The remaining concrete parts can be promptly taken away by hand or an electric pick, and the stud dowels seem to be dynamically undeformed, which is useful for later renovation work. In this way, stud dowels can be used to guide Mach waves for efficient disintegration of steel-concrete composite structures. 3. Conclusions Four examples of dynamic disintegration of concrete structures by predicting and controlling wave motion have been introduced. The experimental observations, together with the three-dimensional finite difference simulations, have clearly indicated that the dynamic development of waves and fracture and final pattern of structural disintegration induced by electric discharge impulse (EDI) depend very sensitively on the geometrical and loading settings. In the first case, the combination of outbound and inbound tensile cracks guided by three-dimensional direct and reflected waves makes the final fracture pattern while in the second case it has been shown that a group of empty dummy holes can guide the propagation direction of the main crack. More practical third and fourth cases have indicated the important role of pre-existing inhomogeneities like slits and interfaces. The wave-based blast design for controlled dynamic disintegration summarized here is effective not only for application of EDI but also for conventional blasting by explosives. Acknowledgements The technical support by Nichizo Tech, Inc., is kindly acknowledged.