| In Japan and European countries such as Switzerland、 Italy、 and France、 many rockfall protection galleries have been constructed over highways along mountains and coastal lines with cliff to protect humans and vehicles from falling rocks. Usually、 sand or gravel cushion has been set on the roof of the galleries to absorb the impact forces due to falling rocks. Usually、 a sand cushion has been used in Japan and gravel cushion obtained from a source near the construction site、 in European countries. On the other hand、 to establish the performance-based impact resistant design procedure for these structures、 those ultimate load-carrying capacities have to be adequately evaluated. But so far the evaluation method has not been established yet. From this point of view、 in this paper、 in order to investigate impact resistant behavior of large-scale Reinforced Concrete (RC ) slabs with absorbing material which is a model of the roof of gallery、 once-only and consecutive falling-weight impact tests were conducted by varying absorbing materials. The dimensions of slabs used in this study are of 4、000 × 5、000 mm and 400 mm of depth. The RC slabs were simply supported with two opposite edges and the other two edges were free. A 5、000 kg steel weight was used for impact test. Here two kinds of absorbing material were applied; sand cushion; and crushed stone. The slab without any absorbing system was also tested as control slab. The consecutive impact loading tests were conducted from elastic region up to ultimate state of the slabs. From this study、 following results were obtained: 1) applying these cushion materials、 the failure mode can be shifted from punching shear type to flexural failure one; 2) absorbing performance of the sand cushion is superior to that of gravel cushion; and 3) in the case of sand cushion、 the dispersion effect of impact force can be more expected than the case of crushed stone. |
