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Working Paper NCAC 2004-W-001 October 2004 Safety Performance Evaluation of Secure Mailboxes Using Finite Element Simulation & Crash Testing

Secure mailboxes, with locking systems, are becoming more commonly used in recent years. These mailboxes are typically heavier and larger in size than standard mailboxes. These new mailboxes have not been tested and their safety performance when impacted with a vehicle has not been evaluated. In this study, Finite Element (FE) computer simulations coupled with experimental testing is used to investigate the safety of these mailboxes and establish some guidelines on their use and installation. The study is subdivided into three main parts. In the first part a detailed FE model of the mailbox is developed and validated against pendulum crash tests. The second part consisted of conducting parametric finite element analysis, with varied mailbox sizes, heights, mounting configurations, and post sizes, to evaluate the mailbox performance. The varied parameters were selected such that a majority of secure mailboxes are covered in the analysis. The third part of the study consisted of validating the simulations results. A critical case was chosen from the simulations and a full scale crash test with identical parameters was performed. Safety Performance Evaluation of Secure Mailboxes Using Finite Element Simulation & Crash Testing INTRODUCTION It has been estimated that over 10,000 deaths occur yearly due impacts with fixed objects. About 2000 fatalities are due to collision into a pole or a post. Under the pole/post support category, the American Association of State Highway and Transportation Officials (AASHTO) estimates that 70 to 100 people die annually in the United States in collisions with mailboxes [1, 2]. Further more, new trends are observed in mailbox sales. New types of mailboxes, such as secure and vandal proof mailboxes, are becoming more popular. These mailboxes are heavier and larger in size that typical mailboxes. Impact into these mailboxes could be significantly more harmful and could increase the number fatalities and serious injuries. It is therefore important to investigate the safety of these mailboxes and to establish some regulations and guidelines that would reduce the fatalities and risk of injuries associated with them. METHODOLOGY The objective of this research is to investigate the safety performance of secure mailboxes. These mailboxes come in a verity of shapes and sizes. Also varied support systems are available to mount these mailboxes. Evaluating all these cases through only full-scale crash testing would require a large number of tests and could be cost prohibitive. An approach that makes use of finite element simulations coupled with full-scale crash testing is used in this study. In the first part of the study, a detailed search was performed to identify currently available secure mailboxes. During the search process, all relevant data, such as mailbox weight, mailbox dimensions, support type, etc., were gathered. Upon completion of the search, a set of mailboxes and support systems were selected for the study. The selection was made in such a manner that the majority of available secure mailboxes are considered in the analysis. Four different mailboxes were selected and used in the study: the “Belaire 20” which weighs 6.4kg (14lb), the “Belaire 16” weighing 10kg (22lb), the “Senator 16” which weighs 15kg (33lb), and the “Senator 16 XL” with a weight 17.7kg (39lb). Two different post sizes were chosen: a 50mm x 50mm x 1.6mm (2”x2”x1/16”) and a 100mm x 100mm x 3.2mm (4”x4”x1/8”) square tubes. A third parameter that was varied in the simulations is the mounting configuration of post to the ground. Three mounting configurations were analyzed. The first configurations, surface mount, consisted of connecting the post to a concrete foundation through four bolts. In the other two configurations, the post was embedded in soil at 300mm (12”) and 600mm (24”) depths. In the second part of the study, two pendulum tests were performed to validate the secure mailbox model. One of the four chosen mailboxes, the Belaire 20, was used in these tests. The two tests were similar except for the connection of the supporting post to the ground. In the first test, four grade 5 bolts were used to secure the post to the foundation. In the second test, grade 2 bolts were used. A detailed finite element model of the secure mailbox was created and the two test setups were replicated. The model was then exercised to check its validity. Several simulations were performed to identify and correct deficiencies in the model. This process continued until reasonable correlations were obtained between tests and the simulations.