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Chad Goodnight, P.E., PhD
Senior Engineer
BergerABAM
Federal Way, Washington
Scott Branlund, P.E., S.E., M.ASCE
Senior Project Manager
BergerABAM
Federal Way, Washington
Doug Playter, P.E., M.ASCE
Senior Project Manager
Jacobs
Bellevue, Washington
Tim Doggett, S.E.
Technical Engineer
Alaska Department of Transportation and Public Facilities, Alaska
This paper discusses design aspects of the guide-pile dolphin restraint system for a precast/prestressed concrete float that will serve as an end berth for the new Alaska Class Ferry (ACF) day boats at the Haines Ferry Terminal. The ACF day boats planned to operate between Juneau, Haines, and Skagway will offer significantly faster loading/unloading operations through the bow and stern doors. The concrete float designed is 150 feet long, 120 feet wide, and 17.5 feet deep (45.7 by 36.6 by 5.3 m) and contains two landside transfer bridges which enable loading/unloading of the ACF. The float will be entirely precast at an off-site plant before being towed to and installed at its final location.
The guide-pile dolphin restraint system limits the horizontal movement of the float while accommodating tidal fluctuations of up to 30 feet (9.1 m) and heave, roll, and pitch under wave loading. The system resists wind and wave loads, accidental vessel impact loads, and potential liquefaction-induced lateral spreading from a seismic event. The system consists of two 4-pile dolphins at the north face of the float and one 8-pile dolphin centered at the south face between two land-side transfer bridges. The dolphins use 36 inch diameter (91.4 cm) plumb and batter piles supplemented with 3 inch diameter (7.6 cm) post-tensioning bars anchored into rock to meet the estimated high uplift demands. Distribution of forces within the system involves consideration for the tidal range, the relative dolphin stiffness, and the influence of in-plan float rotations (yaw). Guide frames consisting of built-up steel members and fender assemblies transfer forces through contact with the dolphin guide-piles. This paper is focused on the design of the restraint dolphins, guide frames, and their connections to the concrete float.