Incorporating the Latest Materials
With Sound Construction Techniques Promises to Reduce Bridge
Life Cycle Costs
By Joseph L. Romano, P.E.
The I-95 Interchange at Scotch Road incorporates the latest
construction materials along with sound and proven construction
techniques with the goal of reducing the total bridge life-cycle
costs while providing the public with a functional, aesthetically
pleasing structure. The project is owned by the New Jersey Department
of Transportation (NJDOT) and was designed by Arora and Associates,
P.C. The interchange is located along I-95 where Scotch Road
(CR 611) crosses over I-95 in the townships of Hopewell and
Ewing, Mercer County, New Jersey.
The bridge, currently under construction, will be an approximately
300-foot-long, two-span, continuous structure. It will replace
an older, functionally obsolete bridge and incorporates the
latest advances in steel and concrete manufacturing. To increase
the long-term effectiveness of these materials, the superstructure
will be made continuous at the pier and will be supported at
the ends by integral abutments. Therefore, the entire superstructure
will be jointless and many of the problems associated with bridge
deck joints, such as maintenance of bearings and rusting of
steel, will be reduced. Eliminating deck joints also significantly
reduces the chance of excessive corrosion and, hence, repairs
to the girder ends.
The superstructure is comprised of unpainted high-performance
steel (HPS) welded plate girders supporting a composite high-performance
concrete deck slab. HPS is superior to conventional steels in
that there is tighter control of the basic steel alloy elements
that ultimately enhances the performance characteristics of
the steel. Therefore, HPSs have better weathering, weldability,
and toughness properties.
A high performance concrete (HPC) deck slab also will be used
on this bridge. HPC structure is not new to the bridge construction
industry. States such as Texas, Colorado, Virginia, Nebraska,
Washington, New Hampshire, and New Jersey currently have bridges
in service using HPC elements. Compared to conventional concrete,
HPC has a decreased permeability to chlorides and other materials
that can cause reinforcement to corrode. Arora and Associates
and NJDOT engineers worked in cooperation to develop the specifications
and design details for the newer materials used on this project.
Using pile-supported integral abutments reduces the initial
and the total life-cycle costs. Labor and material costs are
significantly lower with integral abutments than with conventional
abutments. A further reduction in the initial cost was realized
by reducing the span length and placing the pile-supported integral
abutments behind mechanically stabilized earth (MSE) walls in
lieu of full-height abutments.
A reduction in long-term costs can be realized through the
elimination of the bearings at the abutments. Potential corrosion
of the bearings at the pier also has been addressed. Although
the deck is continuous over the pier, the potential for corrosion
in the fascia bearings still exists because of their direct
exposure to the weather. The interior pier bearings also are
susceptible to corrosion because of the "up-splash"
of moisture from the traffic below the bridge. To address this,
steel drip plates, a common detail for use with weathering steel,
have been welded above and below the bottom flanges of all girders
to intercept water from being deposited on the pier cap and
bearing area from the girders. These drip plates also aid in
the prevention of substructure staining.
Weathering steels require no finished paint coating. This thin,
protective coating of rust that forms on the girder shortly
after fabrication and blast cleaning gives the girder a natural
reddish- brown color and protects the steel from future corrosion.
Using weathering steel eliminates the initial and future maintenance
task of painting the girders.
When completed, the bridge will aesthetically complement this
portion of I-95, which is located within a cut section that
exposes the reddish-brown fracture shale common to the area.
The use of unpainted weathering steel girders, decorative chain
link fencing on the bridge, and selective pier-cap staining
will complement the earth tones present in the area. In addition,
the MSE walls in front of the integral abutments will have an
architectural finish and also be stained to contrast yet complement
The use of newer and more durable construction materials has
an important role in reducing overall bridge life-cycle costs.
However, the enhanced features of the materials and bridge elements
have a better chance of performing as intended when they are
incorporated with sound, cost-effective detailing and design
techniques. The Scotch Road bridge intends to make this marriage
a success. The construction of the Scotch Road and I-95 interchange
began in the summer of 2001. The expected completion date is
the summer of 2003.
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