Advanced High Strength Steels in Rear Underrun Protection Devices

A Rear Underrun Protection Device (RUPD) is a safety feature installed on the rear end of chassis of trailers, designed to prevent smaller vehicles from sliding underneath the rear of the trailer in the event of a collision. Therefore, it plays a critical role in reducing the risk of serious injuries or fatalities. The RUPD standard is updated aiming to improve the strength and resistance of these devices, therefore improving the road safety. This paper shares the author’s experience with the latest standards and regulations for Rear Underrun Protection Devices (RUPD), with a focus on the use of Advanced High Strength Steel (AHSS). It provides a general overview of RUPD standard requirements and suggests several AHSS steel tube sizes suitable for the main longitudinal member, serving as a starting point for design. Key design parameters and potential failure points in RUPD structures are discussed, along with possible solutions. Finite Element Modeling (FEM) is commonly used in the design phase to assess structural performance before physical testing. Given the high costs of prototyping, FEM accuracy is crucial. The paper highlights common sources of inaccuracy—mainly related to modeling techniques—and suggests ways to improve reliability.