Interpretation ID: aiam2907
Manager
Engineering Services
Blue Bird Body Company
P. O. Box 937
Fort Valley
GA (sic);
Dear Mr. Milby: This responds to your September 20, 1978, letter asking whether particular bus body joint is subject to the requirements of Standard No. 221, *School Bus Body Joint Strength*. The joint in question is the connection of two body panels under which runs a continuous body member for the entire length of the bus body.; Standard No. 221 establishes strength requirements for body pane joints which are defined as 'the area of contact or close proximity between the edges of a body panel and another body component...' Body panel is further defined to mean 'a body component used on the exterior or interior surface to enclose the bus' occupant space.' The exterior body panels to which you refer are involved in the enclosure of the bus' occupant space, and accordingly, their connection is a joint falling within the requirements of the standard. The fact that an underlying body member runs under the panels perpendicular to the joint in no way excepts the joint from the requirements of the standard.; Your analogy of these panels to rub rails whose joints are not teste according to the requirements of the standard is inappropriate. Rub rails are added on to the exterior of a bus over the body panels. All parts of the rub rails fall outside the exterior skin of a bus, and therefore, they serve no purpose in enclosing occupant space. The panels to which you refer, on the other hand, are the primary sidewall components enclosing bus' occupant space.; You ask how the agency will test this joint since it has a bod structure member that runs perpendicular to it. You suggest that the agency cut an appropriate size specimen of the panels, joint, and underlying body member and pull one panel and the body member against the other panel and the body member. The agency disagrees. This procedure would not test the strength of the joint, since the stresses imposed by the test would be carried by the continuous body member being pulled against itself.; The agency tests such joints by cutting a specimen of the panels tha includes a portion of the underlying body member. The ends of the body member are then removed to allow the testing device to clamp the two body panels that are to be tested. However, rivets or other bonding materials that connect the panels and the body member at the joint remain intact. This is what is intended by the standard's requirement that the underlying body structure be included within the joint strength test. Leaving the underlying structure intact at the joint permits a test of the joint's strength that closely approximates the actual strength of the joint as it is installed in a completed bus.; Responding finally to your last comment that the agency by its testin technique is hindering the development of integrally constructed bodies, the NHTSA disagrees. The agency believes that the strength of the entire bus body is dependent upon the strength of its parts. Each joint must be examined independently to ensure that it is strong enough to withstand accident forces. Since those forces vary with the nature of any impact and can result in severe stress on one small section of a bus, it is appropriate to measure the strength of individual joints. However, the agency's testing technique as outlined above considers the effect of the underlying bus structure thus encouraging the development of integrally constructed bodies.; Sincerely, Joseph J. Levin, Jr., Chief Counsel