How Much Damage Can Underride Guards Take?

FEARS that minor nicks or dings will require underride guards to be replaced are exaggerated, based on results of research conducted by Great Dane Trailers and a new recommended practice (RP) developed by The Maintenance Council.

The Federal Highway Administration last year began requiring fleets to maintain underride guards in the same condition and configuration as they were when new. The response to this requirement was the question of how much damage the guards could take and still meet federal guidelines.

"Underride guards are not as delicate as some of us thought originally," Jimmy Yglesias, director of products, systems, and components for Great Dane said while leading a meeting of the "Techniques for Impact Guards" task force at the 1999 Annual Meeting of The Maintenance Council.

Great Dane tests of underride guards and the TMC recommended practice both reflect a fair amount of resiliency. Yglesias gave these examples:

o Vertical members of the guard assembly may be bent forward three inches at the horizontal member and still be able to comply with force and energy-absorption provisions of the underride guard regulations.

o Deformation of the horizontal member, such as that inflicted by dock locks, will not affect compliance if the horizontal member is not bent upward more than three inches.

o The horizontal member may be bent forward as much as three inches and still comply with force requirements.

o The areas of the horizontal members outboard of the vertical members can be bent upward as much as three inches.

Although damaged horizontal and vertical members still may be able to meet the force and energy-absorption requirements of the underride guard safety standards, the damage may significantly affect the dimensional requirements. For example, the National Highway Traffic Safety Administration specifies that the ends of the horizontal member must be at least four inches from the side of the trailer and that the horizontal member be no more than 22 inches above the ground.

Underride Guidance At the same TMC task force session in which Yglesias shared the results of his company's underride testing, TMC also distributed its recommended practice designed to serve as a guide for the inspection and repair of underride guards. The scope of the RP includes dry-freight and refrigerated vans and platform trailers that are not equipped with work-performing equipment or are otherwise exempt from the requirements of FMVSS 224.

Provisions of the recommended practice include:

o Inspect guards regularly. Look for cracked welds, cracked or fractured vertical members, along with cuts and tears in any member.

o Make sure the guard meets all dimensional requirements.

o If a vertical member of the guard is bent forward, other components of the trailer may be affected. Check the condition of the crossmembers, rear sill, and the last six feet of the floor. Damaged components should be repaired as needed.

Damage Control TMC has specific advice regarding the repair of damaged underride guards. Among the recommendations:

o Horizontal members should be replaced with an OEM-approved replacement member. The member should be made of the same alloy and have the same dimensions as the original. Installations must be made according to the OEM's instructions.

o If an outer segment of horizontal members is bent upward three inches or less, the segment may be more than 22 inches above the ground and, therefore, outside the dimensional requirements of the regulation and must be repaired. If bent downward less than three inches, the fleet may choose to repair the horizontal member or leave it alone.

o Underride guard members that have been bent three inches or less can be bent back to their original positions using cold bending. TMC does not recommend applying heat to help restore the guard to its original shape because heat can diminish the strength of the steel.

o Some impacts will drive the guard toward the front of the trailer without deforming the guard itself. Such impacts may move the horizontal member beyond the maximum 22 inches above the ground or the 12 inches from the rear of the trailer. The guard should be restored using cold-bending techniques. If the guard cannot be returned to its original position, the entire guard must be replaced.

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