Container cranes are used to unload ships in ports and are critical to port operations. Past earthquakes have highlighted the vulnerability of container cranes to damage from even moderate earthquakes. At the Port of Kobe during the earthquake that hit in 1995, a considerable fraction of the container cranes either collapsed or were too damaged to be used again, leading to significant economic losses at the port and surrounding region. Cranes are unique structures and replacement of a failed structure can take more than a year. Their continued operation post earthquake is critical to the continued operation of the port as well as post-disaster recovery for the region in which it is located. Although cranes are vulnerable to earthquakes and critical to the economy, the seismic performance of cranes has not been studied in the United States until now.
Damage in the crane is one of three types. The first type of damage is derailment, which is when the wheels that move the cranes come off the rails that run along the wharfs. This is minor damage. The crane cannot be used while the crane is off of the rails, but it only takes a couple of days to replace the crane on the rail. The second type of damage is localized damage in parts of the crane. This is a more severe type of damage, because the damaged portions have to be repaired or replaced, which can take several months after an earthquake. The third type of damage is collapse. This is most severe, because the whole crane will have to be replaced.
In order to get a better understanding of how a container crane will respond during an earthquake, a 1/20th and 1/10th scale models of a container crane has been designed and tested on the shake tables at the University at Buffalo. The shake tables have the ability to simulate the motions of the ground during an earthquake. The objective of the tests was to capture the movements of the crane from when it starts to shake during small earthquakes through when it collapses due to a large earthquake. The data collected during the test provides information on when each of the types of damage are likely to occur. The 1/10th scale test is largest shake table test performed on a crane in the United States and the first shake table test in the world to look at when cranes would collapse.
The information collected from the test will be useful to port owners and engineers. The information from the test will be used to develop new design standards to protect cranes from extensive damage during future earthquakes. The data can also be used to design retrofit strategies for existing cranes, to protect them from earthquakes.