High Tension Cable Median Guardrail Expected Lifespan

Project summary:

High tension cable median guardrail (HTCMG) systems have been used in the state of Minnesota by MnDOT for the last twenty years. HTCMGs are used on heavily travelled roads to prevent head-on crashes between travelling cars. Three HTCMG systems are typically used in the state of Minnesota namely Gibraltar, Brifen, and Trinity systems. All HTCMG systems are formed by cantilevered steel posts, which provide a guide for pre-tensioned steel cables. The cables are connected at their end to an anchorage system buried in a concrete block. The cantilever steel posts are designed to yield during crashes, which absorbs the energy and relaxes the tension in the cables. The remaining elements are expected to remain undamaged during a crash. Even though there have been studies on the design, optimal placement, and installation procedures for the HTCMG systems, additional studies on their life expectancy are required. It is not clear if aging HTCMG systems, affected by extreme weather conditions and crashes, can operate as intended. A thorough assessment of the HTCMG system requires testing of all the structural elements, in their pristine condition as well as aged conditions (i.e., corrosion) for comparison. Such a broad study is not feasible in a 24-month project. Therefore, we have identified the most critical components of the system to be studied in this proposed project. The following summarizes the objectives of the proposed study: ? Understanding the lifespan of the steel posts within HTCMG systems. Since these elements are replaced after each crash, their life span will be assessed under aging effects (i.e., corrosion). ? Understanding the lifespan of the cable system (including the cable, turn buckle and splice assembly). ? A preliminary evaluation of the concrete anchorage system using code equations for all three common HTCMG systems, followed by detailed finite element analysis of the most critical detail. ? Provide an understanding of the expected lifespan of different components within the HTCMG system, which can be helpful for asset management of the HTCMG system and for assessing whether the frontline employees working on these systems face increased safety risks Document the visual damage on aged components within the HTCMG system that are tested in the study, which could be helpful for developing guidelines for visual examination of different components of the HTCMG system.