# Collision Study on New Aluminum Alloy W-Beam Guardrail
## 2 Structure Optimization of W-Beam Guardrail
### Mechanism Analysis  
In the optimization method for the W-beam guardrail, the gradual reduction of the shell structure characteristics of the guardrail may adversely affect its protective performance. Therefore, to clarify the impact of this change on the impact deformation resistance of the guardrail, LS-DYNA was used to establish collision simulation models for the 36 new types of guardrail beams, and their deformations under the same collision conditions were compared. The dimensions of the 36 new guardrail beams are based on actual measurements, with a uniform thickness of 3 mm. To ensure the validity of the collision model, the wave beam was treated as a flexible body, and Q235 nonlinear structural steel, which accurately reflects plastic deformation, was used as the material. Shell elements were employed for modeling. In the context of instantaneous collisions, damping and dynamic coefficients typically do not significantly influence the results. Consequently, damping and dynamic coefficients were not incorporated in the analysis settings. Additionally, the beam was rigidly connected to the supports at both ends, and the six degrees of freedom of the supports were constrained. The impactor was positioned directly above the mid-span of the beam and given an initial velocity of 5 m per second to simulate the collision. Details of the collision model setup are shown in Figure 3. Nineteen representative sections were selected from the results, and their deformation during the collision was plotted against the moment of inertia. The results are shown in Figure 4.  
The curve as a whole exhibits a trend of first descending and then rising from region 1 to region 2 (Figure 4), where the characteristics of the curve undergo a significant change. In region 1, there is a pronounced negative correlation between the moment of inertia and the deformation (correlation coefficient r = \(-\)0.96, significance coefficient \(p<0.001\)). Conversely, in region 2, a significant positive correlation is observed between the moment of inertia and the deformation (correlation coefficient r = 0.95, significance coefficient \(p<0.001\)). In region 2, with the increase in moment of inertia, the deformation increases. This is because the new cross-sections in region 2 lose the characteristics of shell structures. During the collision process, the wave-shaped beam undergoes localized lateral deformation, leading to a rapid attenuation of the cross-sectional moment of inertia, resulting in a decrease in the stiffness of the wave-shaped beam and thus an increase in deformation. It should be noted that when the wave-shaped beam undergoes excessive deformation, its bending stiffness will sharply decrease, at which point longitudinal tension begins to play a role in resisting the impact force. After comprehensive consideration, the final design of the cross-section dimensions for the new guardrail beams was determined. Under the condition of the same thickness of 3 mm, the cross-sectional area of the new guardrail beams increased by 8% compared to traditional guardrails, and the moment of inertia increased by 28%. The cross-sectional dimensions of the traditional W-beam guardrail beams comply with relevant specifica  
Figure 3: Schematic diagram of the wave beam collision model. The simulation analysis of different sections of the new guardrail was conducted with boundary conditions as depicted in Figure 3. The relevant parameters are as follows: the momentum of the colliding object is 625 kg\(\cdot\)m/s, the span of the wave-shaped beam is 1.6 m, the unit length mass of the wave-shaped beam is 12.5 kg/m, and the material's elastic modulus is 206 GPa. The results are shown in Figure 6, yielding a correction coefficient of 0.67. In the preceding discussion, the corrugated guardrail was simplified as a beam-column system, neglecting the characteristics of the corrugated beam shell structure. Simultaneously, comparing different new guardrail sections revealed a consistent proportional relationship between theoretical and simulation results.