Design Of Steel-BFRC Combined Protection Devices And Analysis Of Its Anti-collision Performance

Scour and vessel impact are the important reasons causing to the damage of a bridge pier,which brings a great challenge to the normal service of the bridge.Protective device plays an important role and significance in all kinds of long span bridges.The installation of protective devices can effectively resist the impact of ships or drifting objects and protect the foundation of bridge piers.However,with the deepening of scour depth,when the bridge is subjected to the combined hazards:scour and vessel impact,the influence of protective devices on the overall safety of the bridge is rarely studied.In this paper,the combined protective device of basalt fiber concrete-steel casing is designed.And its effects on the safety of a bridge under scour and vessel collision is evaluated.(1)Drop hammer and pendulum impact test.Design and complete the basalt fiber reinforced concrete beam drop weight impact tests and concrete-filled steel tubular pendulum impact tests,the dynamic performance of the basalt fiber reinforced concrete beams with different fiber volume contents is studied,the response of concrete filled steel tubular pier systems with different scour depths is evaluated.The results show that the content of basalt fiber has small effects on the impact force,but it has great influence on the displacement.When the volume content of basalt fiber is 0.75%,the best protective effect can be achieved and the cracks on the side of the beam can be well inhibited.At the same impact velocity,the peak displacement of at the top of pier increases with scour depth,and the scour depth decreases the horizontal and vertical bearing capacity of the pile foundation,so the displacement of the bridge pier structure increases significantly.Taking the scour depth of 60cm as an example,the peak displacement of pier top is 31.0mm at the speed of 3m/s,while the displacement of pier top is 17.5mm without scour,increasing by about 77%.(2)Finite element simulation of impact test.Using ANSYS/LS-DYNA,the finite element verification has been carried out on the impact test of the wave-steel plate-UHPFRC combined anti-collision structure in reference[35],the drop hammer impact tests and the pendulum concrete-filled steel tube bridge pier test,which provide theoretical and technical support for the design of protective device and the simulation of full-size bridge collision.The results show that the CSCM constitutive model can be used to accurately simulate the dynamic impact response of fiber reinforced concrete.The CSCM material model is used to simulate the dynamic impact of basalt fiber concrete trabecular beam with 0.75%volume content,which is consistent with the test data after checking.The pile-soil interaction was simulated by soil spring method(p-y,q-z,t-z three-direction spring),and the pile group and soil were separated into a series of beam elements and spring elements,respectively.The experimental data match well with that of numerical simulation.For example,the maximum relative error between test and simulation is only 13.2%for peak displacement of pier top.(3)Numerical simulation calculation of ship-protective device-bridge collision.Taking a three-span continuous bridge as an example,this paper analyzes the interaction between the protective effect,local scour and ship collision through finite FE method,and puts forward some improvement measures for the design of the protective device.The results show that Steel-BFRC protective device designed has good protection effect against scour depth at all levels and collision of two types of ships,which plays a important role in the protection of bridge piers.For example,under the 9m scour depth,the internal energy of the bridge pier is 2.03MJ without protective device,but after the protective device is installed,the internal energy is only 0.2MJ,with a decline rate of 90.15%.And when scour depth is 6m,the cargo ship directly hit the pier will lead to the damage and rupture of the pier,after adding the protective device,even the damage of the pier under the 9m scour is very small.With the addition of protective devices,all kinds of dynamic responses to the bridge are more muted.For example,under the condition of 6m scouring,the peak impact force is 12.3MN without protective device,and it is reduced to 6.36MN with protective device,a drop of 48.29%.With the deepening of scour depth,the decreasing range of the protective device to the dynamic response peak increases as a whole.For example,when there is no scour,the peak displacement of pier top decreases by 4.45%,while scour depth is 9m,the peak displacement decreases by 31.88%.The thickness of inner partition and basalt fiberboard has a significant influence on the protection effect.In this paper,the best protection effect can be achieved when the thickness of inner partition is 9mm and the thickness of basalt fiberboard is 90mm.