Interpretation ID: aiam2266
Staff Engineer
Blue Bird Body Company
P.O. Box 937
Fort Valley
GA 31030;
Dear Mr. Milby: This responds to Blue Bird Body Company's February 13, 1976, questio whether 47 described intersections of bus body components qualify as 'body panel joints' subject to the requirements of Standard No. 221, *School Bus Body Joint Strength*. You also ask what test procedures are used in testing joints if the means described in S6.1.1 or S6.1.2 cannot be employed due to the configurations of the intersecting components.; The terms which establish the applicability of the requirements of th standard to a particular section of a school bus body are defined in S4 of the standard. Read together, they establish the following test. If the edge of a surface component (made of homogeneous material) in a bus that encloses the bus' occupant space comes into contact or close proximity with any other body component, the requirements of S5 apply, unless the area in question is designed for ventilation or another functional purpose or is a door, window, or maintenance access panel. Applying this test to the 47 intersections of bus body components you describe, it appears that the areas corresponding to the following numbered paragraphs of your letter are bus body joints and therefore must meet the 60-percent joint strength requirements: 1, 4, 5, 6, 7, 8, 9, 11, 13, 14, 15, 19, 20, 23, 26, 28, 29, 50.; The front and rear headers described in paragraphs 2 and 12 ar considered primarily structural and have only an incidental role in enclosing the occupant space and, therefore, are not considered 'body panels' for purposes of the requirements.; The wire molding discussed in paragraphs 3 and 10 is considered maintenance access panel, excluded from the requirements only if a wire is installed behind the molding.; The bumper trim strip described in paragraph 17 is not considered t have a function in enclosing the occupant space and is therefore not considered a body component for purposes of the requirements.; Your assumption that components located entirely below the level of th floor line are not subject to the standard is correct. However, body panels that do 'enclose bus' occupant space' because a portion lies above the floor line are subject to the requirements. Thus, the rear center skirt described in paragraph 16, the bumper trim panel described in paragraph 18, and the auxiliary cross members described in paragraph 21 are not subject to the requirements.; The rubrails described in paragraphs 22, 23, 27, 28, and 29 are no themselves considered to have a function in enclosing the occupant space and therefore are not considered body components for purposes of the requirements. For purposes of testing the complex joints to which they are fastened, they should be modified as necessary to prevent them from affecting testing of the underlying joint.; The wheelhousing trim described in paragraph 24 is not considered t have a function in enclosing the occupant space and is therefore not considered a body component for purposes of the requirements.; Because the plywood described in paragraph 25 is attached to a floo panel and is only added to some buses for insulation purposes, it is not considered to have a function in enclosing the occupant space and is therefore not considered a body component for purposes of the requirements.; The extruded aluminum trim described in paragraph 30 is not considere to have a function in enclosing the occupant space and is therefore not considered a body component for purposes of the requirements.; The NHTSA agrees that paragraphs 30 through 36 and 38 through 4 describe joints between maintenance access panels and the bus body. The ventilation duct in paragraph 37 is the type of ventilation space that is not subject to requirements for joint strength.; In many of your requests for clarification, you asked what means woul be employed to test joints in which the two body components in question are not flat surfaces in the same or parallel planes. The NHTSA intends to test joints that are not capable of being tested as specified in S6.1.1 or S6.1.2 by determining the nature of the two body components and testing identical materials joined by the same means as is used by the school bus manufacturer. The materials will be flat and conform to the dimensions described in Figure 1, and they will be oriented in the same fashion as described in Figure 1. For example, the 90-degree angle at the joint described in paragraph 20 is ignored for purposes of the NHTSA test procedure by simulating the joint and using opposing forces in the same or parallel planes. In this way, the agency can examine a manufacturer's technique to see if the fastening method constitutes the exercise of due care in complying with the joint strength requirement.; You also asked what procedure would be used in testing joints wher more than two panels or body components are joined by one fastener (example in paragraph 29). In these cases, the definition of 'body panel joint' in S4 describes several joints, involving one at each intersection area that qualifies as joint. For each pair of components, the tensile strength of the weaker panel is determined, and the joint is required to sustain a load of not less than 60 percent of that tensile strength. For example, in the case of two side panels riveted to a bow, one joint would be between the two lapped panels and 60 percent of the weaker panel would be the test requirement. At the same time, a separate test of the joint between the bow and the panel that contacts the bow would be required, with 60 percent of the weaker component's tensile strength established as the level of strength for testing.; I trust that this discussion will permit a determination of wha portions of your products are subject to the requirements of Standard No. 221 and what test procedures are employed in satisfaction of the requirements.; Sincerely, Frank Berndt, Acting Chief Counsel