The Downtown Crossing bridge project in Louisville, Kentucky is progressing ahead of schedule. Steel work is expected to be completed by late October 2015 and the bridge is scheduled to open to traffic in January 2016. The 642m, $860 million cable-stayed bridge will connect Louisville to Covington, Indiana, doubling traffic capacity across the Ohio River. Its design incorporates measures like flexible tower foundations and a three-tower arrangement to allow for movement, as well as aesthetic elements like unobstructed tower views. Service life modeling was used to design the bridge to last 100 years with minimal maintenance.

1. 10 www.bridgeweb.com Bd&e | ISSUE 80 | 2015
N E W S
C
onstruction of the Downtown
Crossing in the USA is
progressing at an accelerated
pace with all three towers completed
and the bridge deck making connection
with land at the Indiana approach.
Steel work is expected to be completed
by late October and the bridge is due
to open to traffic in January with full
completion scheduled for the end of
2016.
The 642m-long, US$860 million
Downtown Crossing, one of the two
currently under construction in this
high growth metropolitan area as
part of the Ohio River Bridges Project,
will connect Louisville, Kentucky to
Covington, Indiana.
Initiated as a second bridge in
the Louisville-Southern Indiana
region, the Downtown Crossing
will increase regional mobility and
reduce congestion by doubling traffic
capacity over the river. It includes
building the new I-65 bridge with
six northbound lanes, reconfiguring
Spaghetti Junction (I-64, I-65 and I-71),
reconfiguring Indiana roadways and
bridge approaches, and rehabilitation
of the Kennedy Bridge (I-65) with six
southbound lanes.
In 2012, the Walsh Construction
design-build team won the contract to
design the structure for the Kentucky
Transportation Cabinet. Buckland &
Taylor, as a sub-consultant to Jacobs
and member of the design-build team,
was responsible for the detailed design
and erection engineering of the cable-
stayed signature span. The final design
of a highly durable yet inherently
flexible three-tower cable-stayed bridge
was delivered by the team with an
accelerated project schedule.
The superstructure consists of
concrete towers with a composite steel
girder and concrete deck; two main
spans each 229m long, supported by 15
cables spaced at 15m centres along the
edge girders; end spans of 92m each;
and carrying six lanes of traffic.
The design minimises the footprint
for the tower foundations by using
just one row of large-diameter shafts
per tower, resulting in a system that
shortens the installation time and
accelerates the overall construction
schedule.
Additionally, the system relies on
cantilever action of the shafts to resist
overturning moments resulting from
longitudinal loads. As a result, the
bridge will be much more flexible in
the longitudinal direction than a typical
cable-stayed bridge founded on a pile
group foundation system with piles
spaced in both directions.
A notable design aspect is the three-
tower arrangement; a requirement
specified by the owner. Unlike
traditional cable-stayed bridges with
a two-tower arrangement where the
top of the towers are restrained by
back-stays attached to the anchor
piers, on the Downtown Crossing the
taller centre tower is the third tower in
the arrangement and is not restrained
to anchor piers at the top. This results
in a greater flexibility, and a dynamic
behaviour that is more like a bridge
with a longer cable-supported span.
To meet the community’s
requirement for enhanced views of
the downtown Louisville skyline the
team designed the upper section of the
tower with no cross strut between the
legs. The design-build team elected to
eliminate any transverse struts below
deck to reduce costs and improve the
construction schedule. As a result, the
system is also flexible in the transverse
direction due to the lack of struts
between the tower legs above the
foundation.
An additional measure used was to
design the pile caps to extend below
the water surface to provide aesthetic
consistency as water levels vary, and
to prevent debris build-up. Pile cap
construction was accomplished by
use of precast concrete elements as a
base for the pile cap formwork, which
together served as a cofferdam for
placing the pile cap concrete. The team
also designed five-sided pentagonal
individual towers to provide further
visual interest.
The most important feature is the
100-year service life, considering the
fact that inspection and maintenance
activities substantially affect bridge
life-cycle costs.
Service life design is in its infancy in
North America and adds an additional
level of complexity to the design.
Buckland & Taylor explicitly performed
and incorporated a probabilistic service
life design into the design process for
the Downtown Crossing.
The concrete service life design on
this bridge was based on the model
code for service life developed by
the FIB in Bulletin 34, 2006, which
addresses service life design for plain
concrete, reinforced concrete and
prestressed concrete structures, and
implemented in ISO 16204:2012 Service
life design of concrete structures.
This approach matches the bridge to
its environment and takes into account
the actual chloride demands that the
structure will experience on location.
The design of the concrete mix, the
concrete cover over the reinforcing
steel and the type of reinforcing steel to
limit the initiation of corrosion during
its design life is a probabilistic approach
analogous to strength design.
A corrosion protection plan to
provide the bridge with a 90%
probability of meeting or exceeding
its prescribed service life has been
developed by Buckland & Taylor.
Performing this service life design
assures KYTC that the new bridge will
require low maintenance and stand the
test of time.
By John Brestin, vice president &
project director, Buckland & Taylor
Downtown Crossing on target for 2016 completion
Rendering of the Downtown Crossing
(Jacobs)Jacobs)Jacobs
Above: Construction of the Downtown
Crossing under way alongside the
existing structure (Buckland & Taylor)Buckland & Taylor)Buckland & Taylor