Retrofitting Methods and Crashworthiness Analysis of W-Beam Guardrails Under Code Evolution

W-beam guardrails play a crucial role in ensuring the safety of vehicles traveling on expressways. However， due to factors such as increased vehicle speeds and additional pavement layers， many guardrails constructed according to older standards no longer meet current safety requirements and urgently require upgrading. This study made full use of the existing structure of legacy guardrails designed under previous regulations and proposed an upgrade method involving sleeve heightening and the addition of “C”-shaped crossbeams. Dynamic simulation models of three vehicle types impacting guardrails were developed using HyperMesh and LS-DYNA software to systematically analyze the guardrail’s crashworthiness—including guiding， buffering， and restraining functions—during vehicle collisions. The study further investigated the deformation mechanisms of the upgraded guardrail and the vehicle rollover characteristics under the impact of different vehicle types. Full-scale vehicle impact tests were also conducted to evaluate the safety performance of the upgraded guardrail. The results showed that the discrepancy between experimental and simulation outcomes was less than 10%， indicating high consistency. The upgraded guardrail met the Level IV （SB） protection standard specified in the new regulations and notably enhanced crashworthiness.