Pile Design for Use in High-Tension Cable Median Barriers

Cross-median crashes are the most severe type of run-off-road highway crashes. Cross-median crashes represent approximately 2% to 5% of all interstate crashes, yet fatalities and serious injuries occur in as much as 30% of these severe events. Many state departments of transportation (DOTs) install cable median barriers to mitigate the risk of these types of crashes. In research efforts to design a high-tension cable median barrier, a review of several recent crash tests into cable barriers revealed test failures (i.e., vehicle floor pan tearing and penetration into occupant compartment) that were largely caused by a combination of the pile bending strength and cross-sectional geometry with exposed free edges. The bending strength of the pile, embedded in coarse crushed limestone, caused the top of the overridden pile to press up against the undercarriage of the vehicle. The geometry of the pile contributed to sheet metal tearing and penetration into the occupant compartment. Therefore, research efforts were made to design a new, closed-section pile for use in a non-proprietary, high-tension cable barrier system through dynamic component testing and computer simulations using the finite element program, LS-DYNA. A total of 20 bogie (surrogate vehicle) tests were conducted on potential closed-section piles with a 24-in. (610-mm) embedment depth to determine their strong- and weak-axis capacities under impact loading. The pile sections, including hollow structural section (HSS) 3×2×1/8 (76-mm×51-mm×3-mm), mechanical tube (MT) 3×2×11 gauge (76-mm×51-mm×3-mm), and MT 4×2×14 gauge (102-mm×51-mm×2-mm) were evaluated with different patterns of weakening holes. Analysis of test results and simulations indicated that the HSS 3×2×⅛ with two ¾-in. (19-mm) diameter holes at groundline had the most promising potential to meet the desired strong- and weak-axis capacities, while reducing potential concern of floor pan tearing and penetration. Thus, it was recommended for further evaluation through full-scale crash testing.