Development of Guidelines for Anchor Design for High-Tension Cable Guardrails

High-tension cable guardrail is becoming increasingly popular in median and roadside applications because of the promise of reduced deflections on impact and reduced maintenance. As the performance of these systems is observed in service, there is a growing concern over the end anchorage foundation performance of current systems. Foundations for high-tension systems must not only be capable of restraining the impact load of a vehicle but must also restrain the initial pretension on the cable system as well as temperature-induced loads. Although it may be acceptable for many roadside safety devices to require foundation repair after impact, foundation failure caused by environmentally induced loads would be a significant maintenance problem. Because initial tension-and temperature-induced loads can be greater than those loads applied during impact, these loadings must be considered in foundation design. Foundation deflection can reduce cable tension, increasing deflection of the system during impact and letting the cables sag after impact. The soil conditions in which these foundations are placed vary significantly. The potential impact, tension, and temperature loads were considered, and a set of suggested foundation designs was developed to accommodate a range of in situ soil conditions. These designs vary significantly in different areas around the nation because of variations in both weather and in situ soil conditions. Deflection during full-scale crash tests may not accurately represent the foundation deflection that will be experienced in the field.