Study On The Damage Effects Of Rockfallto Concrete Slabs At Low-velocity

Most highway bridges and buildings were built around the mountains in the western region of China which is also in the seismic zones,the earthquake caused by geological disasters is threatening the buildings.Especially after the 5.12 earthquake,the mountains along the river are loose,the collapse of rockfall occurs more frequently,mountain roads,tunnel shed,bridge collision damage accidents are increasing,mountain rockfall hazard problems are more and more prominent.There was much study on rockfall impacting to bridge pier by domestic and foreign researchers,but the study on bridge slabs is less,slabs has obvious overall response under the effect of low-velocity impact,and is different from the former,is worth further study.Therefore,this article studied and verified the problems above through model test,numerical simulation and theoretical derivation.There are four details parts and results:(1)Concrete slabs low-speed impact testThrough the model test of indoor small size concrete slab,the failure process,the crack form and the influence parameters of the concrete slab under the low-velocity impact load were studied.Experiment showed that the impact time of rockfall to concrete slabs is longer than the rockfall to the piers,the reason is that the collision process included the overall deformation of plate deformation and recovery process.There was a certain relationship between size and thickness,impact velocity and impact strength of concrete.The speed and the thickness of concrete slabs had a greater influence.Concrete strength has a small effect on the target board failure pattern.(2)The numerical simulation of the low-velocity impact parameter optimizationThe finite element model was established by LS-Dyna,for simulating the process of heavy project with low velocity impacting to concrete slab.Optimization of numerical simulation parameters by combined with the model test data,is to make the results much closer to the real situation.(3)Concrete slabs under low-speed impact failure mechanism researchBased on the indoor model test and numerical simulation of damage effects and failure characteristics,the failure mechanism of concrete slab under heavy project with low velocity impact was obtained by combining the plastic plate theory.It showed that bending failure occurred mostly under low velocity and large mass impact,but as the speed increased,local punching failure characteristics of concrete slab center became more obvious.(4)Calculation method derivation of the rockfall impact to the concrete slabsBased on the indoor model test and numerical simulation results,on the basis of predecessors' researches,it was deduced that the rockfall impact force calculation method considering the whole structural deformation.The calculated results and experimental results of the method and the finite element solution are generally low,the deviation was less than 30%,so this calculation method is reasonable.