Impact finite-element analysis of slip-base sign support mechanism

The slip-base design mechanism is used to support signs and luminaries in highways and is designed to break away in crashes with vehicles. This mechanism is intended to minimize occupant injuries by providing reduced resistance to the impacting vehicles. The slip-base mechanism could be sensitive to many design parameters. Conventional design and evaluation of safety performance of these systems by trial and error and crash testing is inefficient, as well as cost prohibitive. Therefore, finite-element (FE) models that can accurately simulate the performance of the slip-base system in various crash scenarios are of essential value. This paper describes dynamic FE models of a slip-base sign support system and its crash performance with vehicles using DYNA3D code. The geometric features, as well as several physical phenomena of components of the slip-base mechanism, e.g., sliding friction, clamping forces, bait-plate interactions, and plate rupture, are modeled and verified in simulation. The FE modeling methods for the required features are described in detail. A validated model of Bogie and its honeycomb material is used as the impacting vehicle. FE crash simulations of Bogie with flexible honeycomb nose impacting the slip-base sign support are validated using the corresponding instrumented crash tests. The simulation model reveals the correct behavior of the break away system response upon impact. The slipping mechanism and Bogie acceleration and velocity responses are accurate as compared with actual crash test results. The FE approach and this validated model can be exercised in numerous crash scenarios for design optimization of other variations of slip-base systems in size, orientation, etc., or for performance evaluation of impacts with various vehicles.