Test and Theoretical Researcj of Prestressed Concrete Berthing Piles

Collision protection facilities in a harbor are mainly used to absorb the huge impact energy when a ship is berthing, thus reducing the impact force and preventing collision between hydraulic structures and the body of the ship. Depending on the stress and the service requirements of the impact prevention facilities, these must have enough elasticity to absorb the kinetic energy of the ship impact and to resist tangential forces. At the same time, they should be wearable and cost-efficient. Berthing piles are one of the major impact-prevention types adopted in port structures. In this method, the piles are arranged directly in front of the structure to undertake impact forces from ships. To this date, the berthing piles in China and overseas are mainly made of steel, and there is little application of prestressed reinforced concrete berthing piles because little research has been conducted on their deformation behavior and energy absorption effects. Based on tests on six post-tensioned concrete berthing piles and a large amount of theoretical computations, we have studied the service performance of prestressed concrete berthing piles. This research work focused on factors that affect the service performance of the prestressed concrete berthing piles, such as concrete strength, pre-tensile stress, sectional reinforcement, cracking characteristics, ultimate bearing capacity and absorption of energy. On the basis of this research, the optimal sectional design of prestressed concrete berthing piles has been obtained. The research contents are as follows:
1. The work performance at service load and ultimate load;
2. The relationship between load and deflection at different loading levels;
3. Crack characteristics and crack closing performance of the berthing piles;
4. Effects of concrete strength on the strain energy of the berthing piles;
5. Effects of pre-tensile forces on the strain energy of the berthing piles
6. Types of stirrups and sectional reinforcement; and
7. The relationship between absorbed energy, reaction force and deformation of the berthing piles using different design parameters.
The actual measured results are consistent with theoretically computed ones, which indicates the correctness of the test scheme and the theoretical computation methods adopted in this paper. The main findings are summarized as follows:
1. The cyclic load tests have shown that when unloading after cracking, the cracks will be fully closed. The good crack closure performance will reduce the steel bar corrosion and greatly help to improve the durability of the prestressed concrete berthing piles.
2. The pre-stress obviously influences the deformation capacity at the later stage of loading. For the members with a high concrete strength, the total deformation ability will be reduced when the pre-stress increases, but for the members with low concrete strength, the result is just the opposite. It is suggested that the pre-stress of the berthing pile should be determined by the premises of guaranteeing a certain cracking resistance during the period of construction and service; meanwhile, it must have a relatively large deformation capacity.
3. Within the range of concrete strength which has been studied in the thesis, the energy absorption ability of the prestressed concrete berthing piles increases with the concrete strength. We suggest that the concrete strength of the prestressed concrete berthing piles is selected between C60 and C80. A small value of the strength should be used when the pre-stress is high, and vice versa.
4. The symmetric reinforcement of the closed rectangular stirrups may provide large energy absorption, lower reaction force, and easy manufacturing, and therefore it is the optimal transverse reinforcement type.
5. The prestressed concrete berthing piles should be designed to minimize the ratio between reaction force and energy absorption. This is not only good to obtain optimal energy absorption effectiveness, but also to have a good crack closure performance.