Behavior of a structurally dissipating rock-shed: experimental analysis and study of punching effects

This article is about protective structures against rock fall. We present a new concept of rock-shed protection: it consists of a reinforced concrete slab (not protected by any ground embankment) supported by specific supports designed to dissipate the energy of blocks hitting on the edge of the slab. The impact energy is dissipated directly by the actuation of the slab and by the damage concrete and reinforcements or by the buckling of the fuse supports. Unlike traditional rock-shed (covered in soil), this new kind of structure must be designed under dynamic load. Experimental trial runs have been conducted on a one-third scale model of a real structure. It appears that three damaging modes have to be considered: the ‘‘concrete compaction’’, punching and bending of the slab. In this paper, we focus on the punching effects. In order to propose a simplified design method, we have determined the experimental value of contact time and percussion load. Then, this load is compared with the ultimate punching load of the slab computed by an analytical model (Mene´trey) and a standard code (Eurocode 2). It results that whenever the percussion load is higher than the ultimate punching load, the slab has been strongly punched.