Container ports are typically located in areas where land is expensive – since air is free stacking higher is an interesting alternative. In countries with medium/high labour costs the combination of high stacking and automation is very competitive and provides a short pay-back for the necessary investment. How then can high stacking be accomplished in port areas where ground conditions are not optimal? Recent land-fills and/ or the presence of clay result in unstable conditions and further storage surfaces are inclined for drainage purposes. A further fact to consider is uneven gantry wheel wear which also must be compensated for.
ABB has supplied automation and electrical scope to a number of demanding automation projects where stacking is carried out from four up to eight high, e.g.:
• Singapore (PSA, 1997) – 39 OHBCs/RMGs
• Tokyo (Wan Hai, 2003) – 6 cantilever RMGs
• Hamburg (CTA, 2003) – 52 RMGs
• Kaohsiung (Evergreen, 2006) – 6 cantilever RMGs
• Rotterdam (Euromax, 2007) – 58 RMGs
• Taipei (New Port, 2008) – 20 cantilever RMGs
• Busan (Hanjin, 2008) – 42 cantilever RMGs
In these projects ground conditions ranged from satisfactory to poor – yet stacking is still being performed with excellent reproducibility. In CTA for example, about 10,000 containers are handled every day.
In the following the basic approach taken by ABB to meet the challenges above will be described.
When placing a container on the ground the exact location will be influenced by a number of conditions including:
• Gantry rail position and slope
• Trolley rail slope
• Girder deflection
• Gantry/trolley wheel position on rail
• Structure deflection
• Load centre influence on ropes
• Load oscillation
• Wheel slippage
In CTA/Hamburg this problem is further augmented by the fact that the two RMGs are located on different tracks with a rail span of 31.0 and 40.1 m respectively. The stacking areas consist of land fill of different quality and rail dislocations were expected.
In order to minimise problems potentially augmented by the two-crane concept the following actions were taken:
• The tolerance of the rail system was set to be about 10x as specified by the German VDI 3576 norm in the direction of the earths rotation
• A mechanical crane design with one hinged and one fixed leg was specified
• A test track with maximum tolerance was laid during 2002 to verify stacking requirements