Technical profile: shipunloaders for earthquake-prone ports
May 01, 1995
by Teresa Acklin
Contributed by suppliers, technical profiles feature new technology, products, specific applications or proprietary concepts. This material was prepared by Vigan Engineering S.A., Nivelles, Belgium.
Although Kobe, Japan, is still suffering repercussions from the massive Jan. 17 earthquake, some grain handling operations at the Port of Kobe resumed relatively quickly.
Kobe is Japan's third largest grain handling port, serving six major flour mills, nine feedmills and seven oilseed crushing plants. All of the processing facilities sustained some level of damage, and the port itself was devastated, with stationary shipunloaders receiving major damage.
Kobe's port terminals are built over three partially artificial islands, Port Island, Rokko Island and Maya terminal, with bulk and general cargo quay lengths of 9 kilometers. Granular fill is retained by concrete caisson perimeter walls supporting the waterside crane rails. Landside crane rails are supported by either piles or beams.
During the 20-second earthquake, the granular fill liquefied and tended to flow, causing excessive pressure on the quay caissons. The caissons dropped, tilted and finally rotated as much as three degrees on the water side.
The erratic movement of the liquefied granular fill created deep cracks and caused the waterside crane rails to spread away from the deformed landside crane rails; the spread measured one meter on Port Island and three meters on Rokko Island. As the support rails diverged, the crane legs buckled at the portal ties, causing major structural damage.
But less than 21/2 months after this disaster, the port again was handling arriving grain cargoes with a pneumatic shipunloader delivered by Vigan Engineering, S.A., Nivelles, Belgium. The NIV 400 shipunloader was the port's only new gantry crane working at full capacity by late March.
Because ports such as Kobe are particularly vulnerable to earthquakes, Vigan incorporates calculations on “quake proof” crane structures in its engineering and design. To enhance stability on moving soil, Vigan shipunloaders are mounted on four twin wheels, with extra large aircraft tires, powered by four hydraulic motors. Each wheel group swivels for even load distribution.
The patented, self-propelled gantry provides built-in safety features. If any wheel is deflated or penetrates the ground, the gantry immediately rests on its low frame beams. Hydraulic pressure controls braking in case of a power failure.
Gantry frame construction includes strong portal beams with ductile frames. The beam legs and portal beams form a ductile frame structure that can withstand accidental collisions and earthquakes without collapsing. To achieve more stability, Vigan frame legs are about one-third the height of normal container cranes and have a lower center of gravity.
Vigan has supplied several ship-unloaders in other earthquake zones and was able to deliver the NIV 400 ship-unloader to Kobe quickly. The ship-unloader is equipped with a diesel generator and two fuel tanks to allow it to operate independently from a power source. Erection and start-up occurred in fewer than 10 days, despite difficult conditions.
The land access to the speared quay had collapsed, settling by three meters. The Vigan shipunloader with its 23.5-meter boom length enables easy discharge of ships directly into barges at a rate of 400 tph for free-flowing grain of 0.75 density.
These operations marked one of the first steps toward restoring Kobe's position as a major port. Vigan also organized an airlift of its mobile pneumatic shipunloaders to assist the area's flour and feedmill operators.