A new breakaway mailbox designed using nonlinear finite element analysis

Abstract

Historically, most of the research conducted on the development of safer, breakaway mailbox supports has been for rural mailbox installations. Consequently, only one full-scale crash test was performed on an urban, neighborhood mailbox installation and was met with unsatisfactory safety performance results. In response to the potential threat to motor vehicle and occupant safety, the Midwest Roadside Safety Facility, in cooperation with the Unites States Postal Service, researched and developed a new breakaway concept for centralized-delivery equipment, such as the Neighborhood Delivery and Collection Box Unit (NDCBU). The new breakaway concept consisted of modifying the existing anchor bolt configuration to include bolts fabricated from a material of higher strength, a lower percent elongation, and a smaller diameter and with a special two-step washer to retrofit existing mailboxes. Nonlinear finite element analysis (FEA) with LS-DYNA was also used to predict the potential for the new breakaway mount and attached mailbox to meet the crash test requirements of NCHRP Report No. 350, Recommended Procedures for the Safety Performance Evaluation of Highway Features. Concept evaluation and refinement was made with the use of several static pull tests, dynamic bogie tests, and severe corrosion tests. Results from the FEA and laboratory testing showed that the new breakaway base should significantly improve the safety performance of the NDCBU.