Interpretation Response #98-0568 ([Truck Trailer Manufacturers Association] [Mr. Donald W. Vierimaa])
Below is the interpretation response detail and a list of regulations sections applicable to this response.
Interpretation Response Details
Response Publish Date:
Company Name: Truck Trailer Manufacturers Association
Individual Name: Mr. Donald W. Vierimaa
Location State: VA Country: US
View the Interpretation Document
Response text:
JUN 23, 1993
Mr. Donald W. Vierimaa
Vice President-Engineering
Truck Trailer Manufacturers Association
1020 Princess Street
Alexandria, VA 22314
Dear Mr. Vierimaa:
This is in response to your letter concerning rollover protection requirements for a specification DOT 406 cargo tank. Specifically, you asked if a manufacturer, who uses two full length parallel overturn protection rails (inverted V rails), can design the rails so that each withstands one-half of the loads specified in 49 CFR 178.345-8(c)(1).
The answer is no. In the case of inverted V rails that run along each side of the top of the cargo tank (not in the center), a rollover will cause a sudden impact of the ground with only one of the rails, then, if and when the tank rolls to 180 degrees, which seldom occurs, the second rail comes into contact with the ground and experiences a differrent kind of loading. Then, if the tank continues to roll, the first railing will be suddenly released of all loading and the total load will shift entirely to the second rail. In such a rollover scenario, it is not reasonable for a designer to distribute the required loading between the two railings.
However, a designer could provide for two inverted V railings to share the distribution of the transverse loading, by providing for transverse bracing to connect the two railings and to treat the entire design as a single device for the purpose of handling the transverse loading. Without transverse bracing, inverted V railings should be considered separate non-load-sharing devices.
Other devices, such as "tombstones" are considered load sharing devices and are symetrically located along the centerline of the top of the cargo tank, so that in a normal overturn scenario, the devices strike the ground simultaneously and each device receives a sudden loading of similar magnitude. In such a case, it is reasonable to distribute the required design loading among all the devices.
If you need further assistance, please contact us.
Sincerely,
Thomas G. Allan
Senior Transportation Regulations Specialist
Office of Hazardous Materials Standards
178.345-8
Regulation Sections
| Section | Subject |
|---|---|
| 178.345-8 | Accident damage protection |