Tests For Buffer And Energy Dissipation Measures Of Pier Protection Structure Under Rockfall Impact

In recent years,for the development of economic construction in the western region,China has increased its investment in traffic construction and built a large number of roads and bridges.Because of the high mountains and gorges in the western region,the routes in these areas will face frequent geological disasters,whether in the construction or operation stage.Rockfall disaster has become a huge obstacle to traffic construction and safe operation in the western region because of its randomness,sudden occurrence and difficulty in prediction and protection.Therefore,it’s protection has become a research issue that can not be ignored.At present,in areas where rockfall disasters occur frequently,most structures and buildings only take horizontal protection,such as covering a protective cushion directly.However,the rockfall in mountainous areas is mostly rolling stones,so the threat to the vertical components of piers and columns can not be ignored.But there are relatively few studies on the protective measures in China.In order to reduce the damage of falling rocks in Alpine canyons to structures such as pier,and considering the influence of factors such as cost and difficulty of engineering,materials with low cost,easy replacement and obvious cushioning effect are selected and combined accordingly.Self designed Ω and S shaped cold-formed steel,which is used in conjunction with XPS,blockboard,reinforced concrete slab,plain concrete slab and silty clay,puts forward three kind of buffer energy consumption protection schemes:steel-foam composite structure,Steel-co-ncrete composite structure,concrete-foam omposite structure.Through drop hammer impact test of impact foundation slab with three protective measures,the corresponding dynamic acceleration of drop hammer,dynamic reaction force of foundation slab support and dynamic strain of steel bar and concrete of foundation slab are obtained,and the relevant calculation and analysis are carried out to explore the cushioning energy dissipation performance of various protective structures.The main research results of this paper are as follows:1.The drop hammer impact test of the steel-foam composite structure under different impact energy,using the plastic deformation of the Ω-shaped steel to consume the impact energy,and increase the impact path through the extrusion deformation of the XPS and blockboard,prolong the impact duration,and weaken the impact effect on the base plate.The test results show that the impact duration of the foundation slab with protective structure is prolonged by 4 to 5 times,reaction amplitude is only about 1/2 to 1/3 of the direct impact foundation plate,and the combined impulse is reduced to about 60%of the direct impact foundation plate.,and the maximum strain rate of steel bar and concrete is reduced from 105 s-1 to 10-1s-1.2.The drop hammer impact test of steel-concrete composite structure under different impact energy is carried out.The impact force transferred to the foundation plate is reduced by the dispersion of the impact effect of reinforced concrete slab on the drop-weight impact force and the consumption of impact energy caused by the plastic deformation of S-shaped steel.Compared with the failure test without protective measures,the duration of impact is prolonged by 4to 5 times,the reaction amplitude is only about 1/9 of the direct impact foundation plate,and the combined impulse is reduced to about 30%of the direct impact foundation plate,and the magnitude of maximum strain rate of steel bar and concrete is reduced from 105s-1 to 10-2 to 100 s-1.3.The drop hammer impact test of concrete-foam composite structure under different impact energy is carried out.The effect of the impact of falling weight on the foundation plate is reduced by the buffering effect of the XPS and powdered clay on the impact of drop hammer and the dispersing effect of plain concrete slabs on impact force.Compared with the failure test without protective measures,the impact duration is prolonged by 9 to 10 times,the reaction amplitude is only about 1/7 to 1/8 of the direct impact foundation plate,and the combined impulse is reduced to about 55%of the direct impact foundation plate,and the magnitude of maximum strain rate of steel bar and concrete is reduced from 105s-1 to 10-1 to 100 s-1.4.According to the test phenomena and relative data of three kinds of protective structures,it can be concluded that the energy dissipation performance of the steel-concrete composite structure is the best.