Bridge structures crossing navigable waterways may be subjected to accidental vessel (ship or barge) impacts. Incidents of vessel impacts with bridge structures occurred increasingly at an alarming rate due to the increase in bridges spanning over waterways and vessel traffic. Worldwide, an average of one catastrophic accident per year involving vessel collisions with bridges was recorded. Several incidents demonstrated that vessel-bridge collisions not only resulted in the loss of life, but also caused large economic losses in repair or replacement of the damaged bridge structures....[ Read more ]

Bridge structures crossing navigable waterways may be subjected to accidental vessel (ship or barge) impacts. Incidents of vessel impacts with bridge structures occurred increasingly at an alarming rate due to the increase in bridges spanning over waterways and vessel traffic. Worldwide, an average of one catastrophic accident per year involving vessel collisions with bridges was recorded. Several incidents demonstrated that vessel-bridge collisions not only resulted in the loss of life, but also caused large economic losses in repair or replacement of the damaged bridge structures.

To understand the characteristics of vessel impact loads on bridge structures and the dynamic response of bridge pile foundations under vessel impacts, a comprehensive centrifuge model test program involving 96 vessel impact tests was carried out on a 2x3 pile group and a 3x3 pile group in centrifuge at 105 g. A pile group installation device and a model vessel controlling device were developed to install the pile group in flight and conduct multiple vessel impacts on a pile group without stopping the centrifuge. The model tests simulated groups of 2 m diameter by 31.5 m long pipe piles. Five major influencing factors related to the vessel (i.e., tonnage, speed, and bow structure) and the bridge pier structure (i.e., superstructure mass and pile group size) were studied. The response of bridge pile foundation protected by two types of fenders was investigated and compared with the response of the foundation without a fender. In addition, numerical modeling of the bridge pier structure under vessel impacts was carried out.

Results of the centrifuge model tests reveal that vessel impact load is influenced by not only the vessel tonnage and impact speed, but also the vessel bow structure, the bridge superstructure mass, and the pile group size. The magnitude of vessel impact load can be reduced by the presence of a fender system. The magnitude of impact load on the bridge pier with Fender A (stiffness = 0.93 kN/mm) is on average 36–39% smaller than that without a fender, while the reduction of impact load by Fender B (stiffness = 2.35 kN/mm) is on average 21–27%. An empirical equation is established to estimate the vessel impact load considering the influencing factors related to the fender systems (stiffness), the vessel (tonnage, impact speed, and bow structure), and the bridge pier structure (superstructure mass and pile group size).

Test results show that the stability of the bridge pier structure increases with the superstructure mass. When the bridge superstructure mass is increased, the magnitudes of pier displacement and bending moments in the pile group decrease. During a vessel-bridge collision process, the inertia force of the bridge pier is mobilized more rapidly than the internal forces (i.e., subgrade reaction, shear force, and bending moment) in the pile group. As the pier displaces, the subgrade reaction of the pile is mobilized, which results in the development of pore water pressures in the soil.

Numerical modeling of 15 centrifuge impact tests was carried out. General agreement was obtained in the trend of the measured and computed load-displacement curves, bending moments, and p-y curves for the 2x3 and 3x3 pile groups. The displacements of the pile groups decrease with increasing bridge superstructure mass, but increase with vessel tonnage and impact speed. The maximum bending moment decreases with increasing superstructure mass of the bridge under the same vessel kinetic energy. The computed and measured depths to the maximum bending moments are located between 5.26 m and 8.42 m below the ground surface. A triangular load model is used to simulate the vessel impact load as an input for analyzing the load-displacement response of the bridge pier structure under vessel impact. The computed load-displacement curve is consistent with the measured curve under the same maximum impact load and load duration.