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In 1961, the world's longest vertical
lift bridge began carrying rail traffic over the Arthur Kill between
Staten Island, New York and New Jersey. The 170-m (558-foot) -long
lift span of this PB-designed bridge surpassed the record held by
the Buzzards Bay Bridge on Cape Cod, Massachusetts, which was also
designed by PB.
The span was designed to be normally kept in the raised position
because of waterborne traffic in the busy Arthur Kill waterway.
When lowered to permit the passage of trains, its vertical clearance
is 9 m (31 feet), allowing smaller vessels to pass without opening
the bridge. The total operating time to raise or lower the span
through its traveling distance of 31 m (104 feet) is two minutes.
The bridge was taken out of service several years ago when freight
service to Staten Island was discontinued. In anticipation of a
renewal of rail freight service to carry freight trains to the nearby
marine container port terminal on Staten Island, the Port Authority
of New York & New Jersey retained PB to inspect and evaluate
the condition of the bridge including its lift span, towers, approach
spans and masonry foundations.
Original Design
The original design contemplated construction of the west main pier
foundation by the Prepakt concrete method in which the cofferdam
was filled with gravel and then intruded with cement grout to form
a concrete plug. At the time of construction, cores taken after
grouting was completed disclosed extensive voids. It was decided
to reinforce the foundation with 14 drilled-in caissons with heavy
steel H-section cores. After the cores were placed in steel casings
drilled through the Prepakt foundation and into underlying bedrock,
the casings were filled with concrete. The 14 caissons were designed
to support the pier independently from the Prepakt foundation.
The Condition Inspection
We were directly responsible for the inspection of the lift span
and towers, operating machinery, electrical controls, track and
signals. We also provided field supervision for the inspection of
the approach spans, underwater inspection of the piers and fenders,
and assessment of hazardous materials on site. The inspection was
done with the lift span in the open (raised) position because it
had become inoperable due to vandalism. After completing the inspection,
we prepared a rating analysis, inspection findings and recommendations
based on our observations.
Our inspection included:
- Computing the load capacity and fatigue ratings
for both Cooper E-72 and 113-metric-ton (125-tons per car) -unit
train loads (Cooper E-72 is the loading for which the bridge was
designed originally)
- Rating all live load carrying members of
the lift span, towers and approach spans
- Member sizes, section properties and forces
were based on the original stress sheets except for the approach
spans, which were field measured because no plans were available
- Computing fatigue ratings for all members
subject to tension due to axial load or bending.
Recommendations
and Cost Estimates
We divided our recommendations for repairs into the following three
rehabilitation categories and compiled estimates for each:
- Return the bridge to reliable operation.
- Rehabilitate for five year service.
- Rehabilitate for beyond five year service.
We also compiled estimates for
annual operation and for demolition and removal of the structure.
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