Damage modes and mechanism of RC arch slab under contact explosion at different locations

Explosion position is random for structures under realistic explosion threats. Understanding the damage modes and mechanism of basic structural members under contact explosion at different locations is the basis for evaluating actual blast resisting performance of members and structures. In this research, two full-scale RC arch slabs were tested under contact explosion at and off the bottom center of mid-span cross section separately. Verified numerical models were established to reveal the damage mechanism by analyzing and comparing the characteristics of stress wave propagation, deformation patterns, and energy transition in the two arch slabs. It is found that the damage modes of RC arch slabs subjected to contact explosion at different locations differed greatly. For the arch slab subjected to centric contact explosion, symmetrical compressive stress waves induced by blast firstly reached the top surface and then reflected as tensile stress waves. The symmetrical deformation of the arch slab experienced two stages, i.e., the compression stage due to the shrunk of the lower portion of slab caused by compressive stress waves, and the expansion stage due to the expansion of the upper portion of slab caused by tensile stress waves. So, the arch slab failed as the cratering on bottom surface and concrete spalling on top surface. Because the reflected tensile stress waves, lateral deformation, and energy distribution were small, little damage could be observed in regions near side surfaces. For the arch slab subjected to eccentric contact explosion, the stress wave stress propagation, deformation pattern and energy transition were asymmetrical. Compressive stress waves reached the top surface and front side surface almost at the same time, so reflected tensile stress waves were generated on the two surfaces almost simultaneously and then propagated into concrete together, which produced a much larger and stronger tensile stress wave overlap and superposition region near the front side surface. Correspondingly, besides the vertical shrunk and expansion of the lower and upper portion of the slab respectively, a significant lateral expansion of front side surface was observed. As a result, the damage was concentrated near the front side surface, and behaved as a triangle fully-penetrated area originated from the detonation location to front side surface.