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Strength Evaluation of Connectors for Intermodal Containers.

pdf icon Strength Evaluation of Connectors for Intermodal Containers. (21230 K)
Lew, H. S.; Sadek, F.; Anderson, E. D.

NISTIR 6557; 41 p. August 2000.


Occupational Safety and Health Administration, Washington, DC

Available from:

National Technical Information Service (NTIS), Technology Administration, U.S. Department of Commerce, Springfield, VA 22161.
Telephone: 1-800-553-6847 or 703-605-6000;
Fax: 703-605-6900; Rush Service (Telephone Orders Only) 800-553-6847;
Order number: PB2000-108102


connectors; containers; evaluation; corner fittings; interbox connectors; latch locks; twistlocks; vertical tandem lifts; test methods


Intermodal containers are used widely in marine cargo handling. In order to facilitate unloading of empty containers from ship to shore, two containers are frequently lifted in tandem. This operation is referred to as "vertical tandem lifting." In this lifting process, the lower container is attached to the upper container by means of interbox connectors at the four comers of the container. During the vertical tandem lifting operation, if one or more connectors are disengaged, the bottom container may be separated from the upper container, thereby creating an unsafe condition to workers below. This safety concern prompted the Occupational Safety and Health Administration (OSHA) to request the National Institute of Standards and Technology (NIST) to study the suitability of interbox connectors for vertical tandem lifting. The NIST study included site visits to port facilities and laboratory tests of interbox connectors. Test specimens included semi-automatic twistlocks and latch locks. The experimental program included testing of twistlocks in tension, twistlock and latch lock assemblies with corner fittings in tension and compression, and shafts of twistlocks in tension to obtain the stress-strain relationship. In addition, measurements were made of the bearing area of the top and bottom cones of twistlocks and the latch on the inner surface of the corner fitting. The study indicated that the tensile capacity of the connection is governed by the strength of the corner fitting. The study also shows that the bearing area of latch locks on the comer fitting is less than that required by the IS0 standards.