Evaluation and Retrofit of CH-TRU Trailers Using Finite Element Analysis

After years of use in transporting Contact-Handled TransUranic (CH-TRU) waste to the Waste Isolation Pilot Plant (WIPP), TRUPACT-II transport trailers began developing cracks in crossmember welds near the trailer’s suspension. Designed in the late 1980s, the transport trailers are 42-ft long, with 10-ft spread-axles designed for a maximum gross weight of 62,000-lbs when transporting up to three TRUPACT-II, Type B, containers. Portemus Engineering was originally contracted to analyze the trailers for compliance with the design requirements of ANSI N14.30[1]. The resulting analyses showed that the suspension crossmembers were highly stressed, and corresponded with the actual locations where cracking was observed to occur. Portemus Engineering was then contracted to design a retrofit to prevent future cracking. The trailer’s main beams were modeled implicitly using shell elements to enable accurate analysis of the variable cross-section. The cross-members were modeled explicitly using beam elements to enable simple extraction of forces and moments for subsequent weld evaluations. The three TRUPACT-II packages were modeled as lumped masses, rigidly connected to the trailer frame at four tie-down locations per package. Linear springs were used to simulate the tractor’s suspension at the kingpin interface and the trailer’s suspension at both axles. Initially, four different bounding load cases were developed to simulate road conditions encountered during normal operation (e.g., spalled roadways, railroad crossings, traversing high curbs, etc.). All loads were statically applied, including the required amplification and cyclic fatigue factors from ANSI N14.30. A fifth bounding load case was later identified as the primary cause of cross-member weld cracking: extreme angle backing or pulling the trailer (i.e., lateral application of the tractor’s forces). Retrofit modifications consisted of a C3×5 channel welded across the front and rear suspension brackets and two diagonal tie-rods between the spread-axle cross-members. The resulting configuration was analyzed and the results showed a significant stress reduction in the suspension cross-members and corresponding welds. Modification and subsequent road testing of the semi-trailers is currently in progress.