Marine Works

The elasticity of fenders is related to the ability to release the stored energy during berthing of vessels. However, it has no effect on the reaction force and the deflection of fender system. The amount of energy that a fender can absorb is dependent on the reaction-deflection curve and is represented by the area under the curve. The higher is the reaction force, the higher amount of energy would be absorbed by the fender provided that the resistance of ships’ hull is sufficient to withstand the force without permanent deformations.

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Depending on the configuration of pier, water could help dissipate part of berthing energy. For instance, for closed docks in which there is a solid wall going down directly to the bottom of seabed, the quay wall will push back all the water that is being moved by the vessel and creates a cushion effect which dissipates part of berthing energy (10-20%). On the contrary, for open dock in with piles beneath and water can flow through the underside of piers, there shall be no cushion effect of water.

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When calculating berthing energy of vessels, there is a factor called “eccentricity factor” which accounts for different berthing energy when the vessel contact the fender system at different locations of the vessel.

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The design of a fender system is based on the principle of conservation of energy. The amount of energy brought about by berthing vessels into the system must be determined, and then the fender system is devised to absorb the energy within the force and stress limitations of the ship’s hull, the fender, and the pier.

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In placing concrete by tremie pipes, hoppers are connected to their top for receiving freshly placed concrete. However, air may be trapped inside the tremie pipes if there is rapid feeding of fresh concrete.

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Let’s consider a pile bent with a top slab supported by two ranking piles, each inclining at an equal angle to the pier slab. In designing such a system, truss action is normally adopted to analyze the pile bent. When the reaction forces of these piles, horizontal forces (e.g. due to berthing and deberthing of vessels) and vertical forces (e.g. superimposed deck loads) are analyzed by drawing a force polygon, it is noted that lateral resistance of the pile bent is dependent on the vertical load, i.e. lateral resistance is small when vertical loads are high.

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The most severe load on piers generally is the horizontal load due to berthing and mooring of large vessels. The design of piers is taken as an example to illustrate the importance of adequate pile founding level. Since the widths of open berth piers are relatively small so that they provide a short lever arm to counteract the moment induced by berthing loads.

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During initial driving process, open-ended steel piles are driven through the soils at their bases. However, shaft friction will gradually develop between the steel piles and soils inside piles at some time after pile driving. The hitting action of driving hammers induces forces to the soil and later it comes to a stage when the inertial forces of inside soils, together with the internal frictional forces exceeds the bearing capacity of soils at pile toes. Consequently, the soil plug formed is brought down by the piles.

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Reinforced concrete is designed to fill the void space inside the steel tubular piles from pile cap to a certain distance below seabed. As mentioned earlier, steel tubular piles above seabed level is assumed in design to be completely corroded when approaching the end of design life. As such, loads from pile caps are transferred directly to reinforced concrete infill instead of steel tubular piles.

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In marine piles, open-ended piles are more often used than close-ended piles to enhance longer length of piles installed. This is essential to provide better lateral resistance against berthing loads and other lateral loads in marine structures.

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