Impact of a reinforced concrete roof slab by falling rocks: experiments and modeling



In mountainous areas where the falling rocky blocks constitute a major hazard to civil structures, the structural systems to protect roads and vehicles are usually rock sheds composed of over pretensioned reinforced concrete elements. This is mainly due to the lack of knowledge of the dynamic effects caused by these falling rocks. A thick backfilling layer that prevents the direct impact of falling rocks by constituting a damping medium commonly covers the roof slab of protection structures. This allows the design of the slab with static dead loads (backfilling, concrete roof and rock weights). Recent experiments were performed in Chambery France on a new type of protection system characterized by a roof slab without damping medium (no backfilling) and simply supported on vertical elements by a set of steel supports. The roof slab resists directly the falling rocks impacts, which cause limited local damage to the impact zone, in case of field impact, or

the yielding of steel supports for boundary impact cases. This new protection system makes it possible to reduce the costs considerably by reducing the dimensions of both the concrete structure and its foundations, it allows continuous uses of the structure trough the repair of the damaged zones in the roof slab or the replacement of the "fuse" steel support after each impact. The aim of the present study is to predict the structural response of the new proposed system by a rigorous three-dimensional modeling of the roof slab and its supporting elements. The analysis introduces the impact load in a way similar to that of the performed experiment, and a stress-strain concrete relationship that allows a realistic representation of the concrete behavior under dynamic loads and its corresponding damages. The comparison of the experimental measurements with those obtained from the present analysis proves the accuracy ofthe built model in predicting the real behavior of the protection structure.

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AUTORI: Berthet-Rambaud P., Perrotin P., Timsah Y., Mommessin M., Mougin J.P., Mazars J., Daudeville L.
Numero di pagine: 45

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