Vessel-bridge collision accidents raised concerns in recent years. A catastrophic vessel collision into the Jiujiang Bridge in Guangdong Province occurred on 15^th June 2007. Three piers of the bridge collapsed and about 200 m of bridge deck fell into the river. This study aims to investigate the failure modes and reliability of bridge systems subjected to vessel collision by centrifuge modeling and numerical modeling....[ Read more ]

Vessel-bridge collision accidents raised concerns in recent years. A catastrophic vessel collision into the Jiujiang Bridge in Guangdong Province occurred on 15^th June 2007. Three piers of the bridge collapsed and about 200 m of bridge deck fell into the river. This study aims to investigate the failure modes and reliability of bridge systems subjected to vessel collision by centrifuge modeling and numerical modeling.

A centrifuge model study into the Jiujiang Bridge accident was conducted. Static numerical analysis was conducted to refine the design of the impact load for centrifuge tests. Completely Decomposed Granite was used to simulate the riverbed soils; cement-sand mortar with different water mix proportions was used to simulate the bed rock, the model piles and the columns of the model bridge. Model bows were designed to mount in front of the model vessels. Two series of tests with different riverbed soil conditions were conducted. In each series of tests, three aluminium model barges were released to hit one bridge pier at different specified speeds, and the impact energy was increased gradually till the failure of the bridge system.

The impact loads resulted from the centrifuge tests were compared with those computed according to the AASHTO provisions. The load patterns included touching, chasing touch and pile back hitting. The characteristics of impact loads such as the impact durations, peak impact loads and various influence factors were investigated.

Several aspects of the responses of the bridge system to the vessel collision were studied: the displacements and accelerations of the piers, the bending moments and internal shear forces in the piles, the pore water pressures in the soil, the observed frequencies of the system, the energy dissipation in the collision process, and the failure mode of the model bridge. It was found that three factors; namely, the pile embedment depth, the vessel velocity and vessel tonnage affected both the impact loads and the bridge system response. The failure of the bridge started from the piles under collision, which were subjected to large complex bending and shear forces. The drag forces in the bridge decks led Pier No. 24 to fail in the same direction with Pier No. 23, and Pier No. 25 failed in the opposite direction.

FB-Multipier, a finite element program, was used in this study to analyze the dynamic response of the centrifuge models in prototype scale. Comparisons were made between the computed and the measured displacements of the three piers simulated in the centrifuge tests.