*Article published in CRANE BRASIL Ed. 76
Increasingly, man has been building close to, over and under the sea, erecting complex structures with the most varied purposes: ports, bridges, oil platforms, wind farms and others, with a common characteristic: the need for lifting, whether in construction , whether in operation.
One of the ways of classifying these lifts is to consider the position of the load and crane in relation to the sea, which mainly gives an idea of the environmental effects to be considered in the lifting project (rigging plan). Are they:
Onshore lifting: Lifting on land, where the crane and the load are on the ground, with no relative movements between them. The amplifications of force and displacement acting on the components are of small magnitude, when performed correctly. Generally, for simple cases, the dynamic analysis is suppressed and a dynamic force amplification factor ranging from 1.05 to 1.15 is used. As dynamic analysis is not done, load movements are not calculated.
Inshore lifting: Lifting in sheltered waters, where the height and period of waves generate small magnitude amplifications, close to the onshore lifting situation. This is the case, for example, of lifting to remove a load from a vessel that is moored in the port, where an on-board crane or a crane positioned on the pier is used. The dynamic amplification factor ranges from 1.05 to 1.15.
Offshore lifting: Lifting in the open sea, where there is a direct incidence of waves on the vessel where the cargo or crane is located. The force amplification can be of great magnitude, reaching 3 times the weight lifted, and the motion amplification can reach tens of times, if there is resonance. Exemption from dynamic analysis depends on the experience of the lift engineer and the type of operation. Examples are lifting for the construction of port access bridges and lifting on oil platforms.
Since it is a qualitative classification, it should not be used as the only parameter for choosing the amplification factors, since what governs the calculation of the lifting is the environmental load (wave, wind, current, etc.) and not the geographic position. For example, is a lift in Guanabara Bay inshore or offshore? It depends. There are places where sheltered water can be considered, but in other parts of the bay, it will be necessary to design an offshore lift.
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