Modeling slip base mechanisms

摘要

Slip base mechanisms are commonly used in breakaway devices for the roadside safety industry; for example, the base of structures such as sign posts, luminaire poles, and guardrail system posts are often slip base mechanisms. Due to the breakaway feature of the slip base, it has considerable potential for reducing the amount of crash resistance, and thus occupant injury, when vehicles inadvertently leave the roadway and strike these objects. The objective of this study was to develop improved methods of modeling slip base structures using nonlinear, finite element analysis. Two bolt preloading techniques were developed and evaluated, including one method which utilized a discrete spring element, and a second method which utilized pre-stressed bolt shaft elements. Both methods produced desired bolt preload, as well as acceptable slip behavior when impacted in a simple shear scenario. However, when the impact conditions became more severe, the model using pre-stressed solid elements was significantly more accurate. The stress-based clamping model was then incorporated into a new cable guardrail system model. Performance of the slip base model was acceptable in both end-on impact and length-of-need impact simulations. Thus, the model was deemed appropriate for use in further development and analysis of existing cable systems, as well as alternate slip base applications.