| Construction |
| Replacement of the George P. Coleman Bridge |
By Michael J. Abrahams, New York, New York, 1-212-465-5185,
abrahams@pbworld.com and
Raymond J. Castelli, 1-212-465-5212, castelli@pbworld.com
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| The Coleman Bridge project was remarkable in many
ways. This article focuses on two aspects-reusing existing caissons
and the construction sequence. |
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Awards for the George P. Coleman Bridge
- 2000 Merit Award, Design for Transportation National
Award. U.S. Department of Transportation.
- 1998 Prize Bridge, movable span category.
The National Steel Bridge Alliance/American Institute of
Steel Construction.
- 1997 Grand Conceptor Award. The American
Consulting Engineers Council.
- 1997 Outstanding Civil Engineering Achievement.
Virginia Section of the American Society of Civil Engineers.
- 1997 George S. Richardson Medal for Single Recent
Outstanding Achievement. The International Bridge
Conference, Pittsburgh, Pennsylvania.
- 1997 Roebling Award. The American Society
of Civil Engineers, Construction Division.
- 1997 Engineering Excellence Award. The
New York Association of Consulting Engineers.
- PB Project of the Year.
Constructed projects category, 1996
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The Virginia Department of Transportation selected PB to provide engineering
services for the replacement of the George P. Coleman Bridge, a major
project intended to reduce traffic congestion. The replacement, which
was to be done on the existing caissons (pier foundations), was selected
from the alternatives proposed in PB's earlier crossing study.
Major Features Established during Preliminary Design
During the preliminary design phase, major design features were established.
The bridge was widened considerably to 23.5 m (77 feet), with:
- Four 3.6-m (12-foot) -wide traffic lanes
- Two 3-m (10-foot) -wide breakdown lanes
- Concrete exterior parapets
- A concrete median barrier
- A lightweight-concrete deck for the truss
and swing spans.
Other design features, while less visible, are equally important to
the swing spans:
- Hydraulic Drives. Instead of what
had proceeded to be a mechanical drive system on the original
bridge, the new bridge incorporates hydraulic drives.
- Power Source. The power supply is
more reliable than that for the original bridge because there
are now two power sources and a backup generator for the entire
bridge. Previously there was only one power source and a backup
system.
- Additional Features. Features added
to improve inspection and care of the span included, for example,
lighted maintenance walkways beneath the roadway and a maintenance
parking area on the approach spans.
Evaluating Existing Caissons
An important consideration in the new bridge design was the reuse
of the existing river caissons to support the heavier loads of the
wider structure. We had to evaluate:
- Surface and subsurface conditions
- The piers' resistance capacity
- Additional loads
- Likelihood of collapse.
Surface and Subsurface Conditions. During the preliminary design
phase, we conducted extensive survey and boring programs to carefully
establish existing surface and subsurface conditions-information needed
to prepare final design plans. The most effective way to measure the
ground's behavior is through soil borings and other on-site tests,
which we conducted at depths of up to 70 m (225 feet). PB's geotechnical
investigations confirmed that the existing river piers could support
a widened bridge.
Resistance Capacity. The adequacy of the existing river piers'
resistance capacity against vessel collision was evaluated according
to the design provisions established by AASHTO's "Guide to Specification
and Commentary for Vessel Collision Design of Highway Bridges"
(1991).
A record of all ships using the channel over a 5-year period was obtained
from the Coleman Bridge operator's logs and used to establish the
size and frequency of river traffic. Because the operator's house
was open all day, the logs provided an accurate record of traffic,
included the name of each vessel or tug boat and the number of barges
being towed, as well as the time and direction of travel.
Additional Loads and Frequency of Collapse. We used a 3-D non-linear,
finite element soil-structure interaction analysis to establish the
lateral load response for a ship collision load. These capacities
were compared to the force generated by the ship population drawn
from the 5-year history. We then were able to compute the annual frequency
of collapse for the full range of ships and demonstrate that it exceeded
10,000 years.
Therefore, no large-scale independent protective structure was required.
The existing timber rub strips and the river piers were replaced with
a more modern rubber fender system, however, to provide protection
against minor vessel impact.
Construction Includes Floating The Spans
into Place
The original plans called for a temporary floating bridge to be located
just upstream of the existing bridge to carry traffic during construction.
The legislature voted against this option, however, because of costs
and the inconvenience of a detour. (We had been planning all along
to replace the superstructure using float-in techniques for a number
of reasons.)
As a result of the vote and the need to minimize detour time for traffic,
contract provisions were developed to provide a large incentive for
the contractor to minimize the bridge shutdown. Construction for the
bridge widening took place in three phases plus preparation and final
cleanup while the superstructure was replaced.
Preparation. Preparation included widening the tops of the
river piers, land piers and abutments. The widening of the land piers
and abutments was done with added piles, widened footings and widened
pier shafts and abutment stems. At the same time, the six new river-crossing
truss sections were built off site. These sections were two swing
spans, two anchor spans and two suspended spans. The swing spans were
each 154 m (500 feet) long-some of the largest in the world. Normal
traffic continued on both the river and bridge during this phase of
the work.
Phase 1. New outside lanes were built at both ends of the bridge
at the land piers. Normal traffic continued as new construction was
kept outside of the existing traffic lanes. Then traffic on the approaches
was shifted to the newly constructed outside lanes and most of the
existing inner lanes were demolished and replaced.
Phase 2. The existing truss sections over the river were removed
and the six new truss sections, which had been constructed 60 m (40
miles) from the site, were floated in and the bridge was opened to
traffic-all within 9 days.
Phase 3. After the river truss sections were replaced, traffic
was shifted to the newly built outer lanes on the approaches. The
remaining existing inner lanes on land were demolished and rebuilt.
All four lanes were opened to traffic after temporary barrier curbs
were removed and final roadway striping placed.
PB provided extensive construction services, including the provision
of a resident engineer, continuous field consultation, and mechanical
and electrical assistance for the installation of machinery and controls
for the swing spans as well as for the automated vehicle identification
(AVI) system. We also provided shop drawing review and were responsible
for the preparation of as-built drawings.
The bridge, which was dedicated on August 2, 1996, has won a number
of awards, as shown in the box above. |
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| Ray Castelli has 25 years experience in conducting
and managing geotechnical investigations, foundation design and construction
services for major bridge, marine and tunnel projects. He is Operations
Manager of the Geotechnical and Tunnelling Division in PB's New York
City office. Ray is a member of the Deep Foundations Committee of
American Society of Civil Engineer's (ASCE's) Geo-Institute, a corporate
representative to the International Association of Foundation Drilling
(ADSC), and a licensed professional engineer in four U.S. states
Michael Abrahams is a structural engineer with more than 30 years
of experience, primarily in movable and floating bridges. He recently
authored the chapter on Movable Bridges in the Bridge Engineering
Handbook, published by CRC Press.
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