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Buildings / Bridges

Delaware River & Bay Authority

Vessel Collision Protection for the Delaware Memorial Bridge

Location: New Castle, Delaware and Pennsville, New Jersey • Delaware River

S. T. Hudson Engineers was asked by the Authority to prepare a risk-of-collision analysis based on the latest AASHTO procedures and to identify a "design vessel." Hudson's first task was to investigate methods of primary and secondary protection for the bridge piers in the event of a vessel collision. Hudson's study, after an initial review, was concentrated on the bridge tower piers; the anchor piers are of much more massive construction, and due to decreased water depths, could only be approached by smaller, shallower draft vessels.

Three (3) principle methods of providing primary protection to the bridge tower piers were investigated:

• An "artificial island" surrounding each pier
• Pile-supported, reinforced concrete dolphins, placed to intercept an incoming vessel headed for a bridge pier
• Large-diameter steel sheet-pile cells, filled with granular material (crushed stone or sand and gravel), similarly placed

The artificial island and pile-supported dolphin approaches were abandoned after an initial investigation, and efforts concentrated on the third option; steel sheet pile cells. A cell diameter of eighty (80) feet was selected because, while it is close to the upper limit of economic constructability, it will provide sufficient mass and structural integrity to absorb the bulk of the kinetic energy of the design vessel. Any of the primary protection approaches discussed would result in damage to the impacting vessel, should such an event occur, and to the protecting structure. Such a tradeoff is regarded as acceptable, however, compared to the potentially catastrophic result of full vessel impact on a bridge pier.

Marine Exchange

Cape Henlopen, Ship Reporting Center

Location: Lewes, Delaware • Delaware Bay/Atlantic Ocean

S. T. Hudson Engineers designed the interior and exterior renovations of this World War I vintage lookout tower. The site has been the reporting station for ships arriving and departing from the Delaware Breakwater since 1875. New construction features included coated or galvanized steel framing and siding, internal floors and stairways, HVAC and electrical systems, sleeping accommodations, sanitary and kitchen facilities, fire escape, emergency generator, and grounding/lighting protection for radar and communications antenna systems.

Conoco Phillips

Rehabilitation of the Ship Dock

Location: Trainer, Pennsylvania

S. T. Hudson Engineers performed underwater inspection of the ship dock and found the ship dock required extensive repairs. A feasibility study was prepared to determine the most economical means of rehabilitating the dock while keeping the crude oil dock in service. The scope of service included federal and state permit applications, construction documents for a new approachway, mooring and breasting dolphins, walkways, loading platform and demolition of existing structures. Hudson is ensuring that the installation of temporary walkways and product piping supports, construction of a new steel pipe pile-supported concrete approachway, and partial demolition of the existing timber low deck structure was in accordance with specifications. Construction is ongoing—four (4) new steel pile-supported reinforced concrete mooring dolphins have been completed in August 2007. The complete rehabilitation of the ship dock is anticipated to be the end of 2008.