Experimental Syudy On Rockfall Resistance Of Overhead Roof System With Metal Energy Consumption Bearings

With the frequent occurrence of geological disasters such as earthquakes in recent years and the vigorous development of mountain construction in China,the threat of rockfall to buildings was growing.Because of the high impact energy and speed of the rockfall itself,the impact of the disaster was very bad.At present,there ware few experimental studies on rock fall protection of roof and shed cave roof,and most of them use various covering cushions to play a cushioning role,so the energy dissipation effect of the structure was not ideal.Aiming at the problems of road,bridge,shed and roof rock falling disaster protection,the energy dissipation and cushioning performance could be effectively improved.Combining with overhead ventilation roof structure,metal energy dissipation device and greening roof concept,a new rock fall protection system using metal energy dissipation support to support protective plate and form overhead layer as protective structure was proposed.Through rock impact test,the dynamic impact reaction force,impact acceleration,dynamic strain of steel bar and concrete at the bottom of the platform plate ware collected by the test instrument.The test phenomena before and after the test are analyzed and sorted out,and the cushioning energy dissipation effect of each protective system was summarized.The main research results of this paper ware as follows:(1)Quasi-static loading tests showed that the unequal-diameter double U-type bearings and bracket-type bearings belong to energy absorption structures of type I and type II,respectively.The unequal-diameter double U-type bearing had long enough deformation displacement,and its loaded gradually stabilizes with the increase of displacement,tend to be constant,and the energy dissipation capacity of the structure increases linearly with the displacement.In addition,mechanical stretching could achieve the purpose of reuse,and it was an ideal energy dissipation buffer bearing device.The bracket support had a strong energy dissipation capacity,and the PVC pipe played a certain role in restraining the deformation of the bracket support.(2)Through the finite element simulation of unequal-diameter double U-shaped structure,the optimum inner diameter ratio of upper and lower U-shaped structure was 5/9 under a certain thickness size.Compared with the static pressure test data,it was proved that the load-bearing and energy-dissipating capacity of the structure could be changed by changing the thickness of the structure.At the same time,by comparing the stress and strain distribution nephogram in the process of structural deformation,it was concluded that the strain mode of the structure is geometrically large deformation,material small strain,and the stress and strain of all points of the structure ware basically the same,and the whole structure changes uniformly,giving full play to the deformation performance of the material.(3)According to the drop weight impact test of each protective system and the comparison of relevant data,the overhead roof system formed by the combination of unequaldiameter double U-shaped energy-dissipating cushion bearing and steel meshed concrete protective plate had the best energy-dissipating effect.The unequal-diameter double U-shaped support consumes 14-25%of the impact energy,and the energy-dissipating capacity increases with the increase of the impact energy.The reaction force at the bottom of the plate was only 6%of that under unprotected condition,and the impact duration was 3 times longer than that under unprotected condition.(4)As cushion material,the soil layer had good cushioning effect and can effectively reduce the impact of drop hammer on the protective plate.Compared with the case without soil layer,the peak value of impact acceleration and theoretical impact force decreased by 84.6%and the average impact force decreased 85%,and the impact time increased by nearly 20 times.At the same time,the reaction force of the base of the platform plate is reduced by 30%and the total impact energy was consumed by 15%,which proves that the soil layer had a good energy dissipation effect.The steel meshed concrete protective slab has stronger load-bearing capacity,and its energy consumption effect was 10%higher than that of ordinary concrete slab.