INVESTIGATION OF FENDER SYSTEMS FOR VESSEL IMPACT

Fender systems are currently placed between channel piers of bridges crossing navigable waterways, to guide vessels through the navigational channels. These systems are not designed to withstand any lateral load. This report presents evaluation of the existing bridge fender structures for an impact with a Jumbo Hopper barge and their possible retrofit analysis. The finite element method was selected for the modeling of the fender systems and the impact simulations. Two different analyses were performed: a static analysis with ANSYS using the equivalent force equation from AASHTO (1991), and a dynamic analysis with LS-DYNA where the model of the barge is included. It was found that the present Florida Department of Transportation fender configuration is very weak, and unable to support any significant barge impact force. Failure occurred at the cables connecting piles in the fender system. A retrofit scheme with steel plates connecting the piles showed limited success in barge impact resistance. Corrosion concerns may preclude the use of this retrofit. Another retrofit scheme using concrete wedges between piles was more effective in substantial energy absorption. However, the equivalent static force absorbed by the improved fender was relatively smaller. A cost-benefit analysis is needed to gauge the advantages of fender retrofit in relation to economic design of the actual bridge structure and rebuilding of fenders after an impact. Plastic lumber fenders and piles may be effectively used in fender systems, especially in consideration of long-term durability and economics.