# Design and Simulation Analysis of a New Type of Assembled UHPC Collision Avoidance
## 2 Device Construction Design and Finite Element Modeling
### Finite Element Modeling
#### 2.2.1 Finite Element Modeling of UHPC Collision Avoidance Device  
The collision avoidance device is modeled by an 8-node solid element SOLID164 arrangement, with a total of 18,907 elements. The reinforcing bars are simulated by link element LINK160, with a total of 44,882 elements, and the internal support elements are modeled by 3-D beam element BEAM161, with a total of 319 elements. Considering that an impact is an instantaneous dynamic response process, the steel bar elements and concrete elements are joined by common nodes in the simulation, without considering the lag of the bond-slip reaction between the steel bars and the concrete. The solid element SOLID164 arrangement is also used to model the rubber drums, the outer rubber damping material, and the inner rubber sliders. To facilitate the modeling and reduce computing time, the rotation of the rubber drums is realized by setting appropriate dynamic and static friction coefficients. The finite element model of the collision avoidance device is shown in Figure 6. The finite element model of the outer wall reinforcement and internal support elements of the buoyancy tank is shown in Figure 7. To simulate the buckling and crushing failure of the UHPC box walls, rubber drums and the inside and outside rubber materials in the finite element model, the * MAT_ADD_EROSION erosion failure criterion [29] is introduced to control the failure of the deformed elements. When the strain on an element is greater than the value set for the failure strain of its material, that element is deleted. Thus, the negative volume phenomenon is avoided. The connections of the UHPC box wall with the inner and outer rubber materials are simplified as common joints. The rubber constitutive model adopts the * MAT_MOONEY-RIVLIN_RUBBER model using values of the density, p = 1600 kg.m\({}^{-3}\), Poisson's ratio, u = 0.4995, and the strain rate parameters C\({}_{01}\) = 0.15 MPa and C\({}_{10}\) = 0.6 MPa [30].  
Figure 5: Internal structure of No.3 box.  
The material of the UHPC collision avoidance device adopts the HJC (Holmquist-Johnson-Cook) [31] constitutive model under large strains, high strain rates and high confining pressures. This model takes into account material damage, strain rate, and the influence of the hydrostatic pressure effect on the yield stress. However, there are many parameters in this model and there are no HJC model parameters suitable for the UHPC materials with strain rates corresponding to an impact. Therefore, the research team conducted uniaxial compression, bending, and tension tests, uniaxial cyclic loading and unloading tests, and uniaxial SHPB impact tests on the UHPC materials with strength ratings of C130, and obtained the maximum failure principal strain of 0.01 [32]. By referring to the existing literature [33; 34; 35], the parameters of the HJC constitutive model of the UHPC material are calculated and analyzed. The parameters are detailed in Table 1.  
Figure 6: Finite element model of the collision avoidance device.  
Figure 7: Finite element model of reinforcement and supporting elements.  
The finite element program ANSYS/LS-DYNA is used to verify the SHPB(Split Hopkinson Pressure Bar) impact test of super high performance concrete, Figure 8 shows the SHPB test setup. The results in Figure 9 show that the equivalent stress, \(\sigma^{*}\), is highly dependent on the equivalent hydrostatic pressure, \(p^{*}\). The test and finite element model results are substantially coincident. The rationality and validity of the HJC model parameter measurement method are verified, and the accuracy of the numerical simulations with respect to the performance of the new UHPC collision avoidance device is guaranteed.