All of the traveling cranes at the port of Kobe were damaged by the strong ground motion of the Southern Hyogo Prefecture Earthquake in 1995. Seismic isolation systems for traveling cranes were developed to increase earthquake resistance against strong ground motions. In general, the isolation systems for traveling cranes for strong ground motions are very large. Quays which are not reinforced have a risk of being damaged by strong ground motions, and require traveling cranes to prevent derailing during middle strong motions, because derailing leads to collapse of the traveling cranes. A mechanism for preventing derailing of material handling equipment was developed for middle strong ground motions.
A middle rocker beam of the new mechanism is divided into two beams, and uplift motion of a leg of a crane can be absorbed by rotating motions of the two beams. This allows the mechanism for preventing derailing to be easily installed into the established equipment. Seismic analyses using an finite element model of the traveling crane and vibration tests were conducted to verify the validity of the design and derailing prevention performance. The results of analyses and vibration tests showed that the mechanism for preventing derailing can prevent wheels from derailing during middle strong earthquakes. The configuration of the mechanism and the results of the analyses and vibration tests are presented in this paper.