West 106th Street Bridge Preservation Project
at Nine Mile Creek
What is proposed
The 106th Street bridge as seen from Nine Mile Creek.
The West 106th Street Bridge will be closed during the summer months of 2009 for a Bridge
Preservation Project. City and State bridge inspectors have noted areas of the bridge that have
deteriorated since the original construction was completed in 1969. The bridge maintenance
includes replacing abutment bearings, concrete deck repair and concrete overlay, expansion
joint replacement, approach panel repair, steel reinforcing and retaining wall protection for a
pedestal bearing. The bridge plans are being prepared by SRF Consulting Group, Inc.
Traffic warning signs will be installed two weeks in advance of the work to warn users of the
closure. A detour route will use West Old Shakopee Road, West 100th Street and Humboldt Avenue
South. The existing pedestrian bridge, park parking lot and trail (below the bridge) will all
remain open, except as temporarily closed for safety concerns.
Why close the whole bridge? A complete closure was preferred over a partial
closure to complete the work as efficiently and safely as possible. Maintaining traffic during
construction would:
-
Extend time required for the work, possibly into the regular school year.
-
Cost approximately 25-50% more.
-
Increase traffic congestion, reducing safety of the traveling public and construction
workers.
-
Reduce the area available for construction staging.
Bridge history
The bridge was designed by Howard, Needles, Tammen & Bergendoff, now known as HNTB, an
architecture and engineering firm with a branch office in Minneapolis and headquarters in
Kansas City. The 106th Street Bridge received the Most Beautiful Short Span award from the
American Institute of Steel Construction in 1969. The 106th Street Bridge is unique in the
state of Minnesota, as it is the only rigid "K" frame bridge with only two main girders. Six
others exist with more than two main girders. SRF recently completed a maintenance project on
one of these in Moorhead, MN. The 106th Street Bridge was also one of the earliest bridges to
use weathering steel, also known as Cor-Ten Steel, which uses the natural rust patina as a
stable barrier to prevent further corrosion.
The bridge is considered "fracture critical," a term that describes a design that does not
offer built-in redundancy to prevent failure if one of the load bearing girders fails. This
does not mean the bridge is unsafe, and it is a completely different design than the I-35W
Bridge that collapsed.
The bridge, an important transportation link, crosses the Lower Valley of Nine Mile Creek,
which has been prized for many years as a premier recreational area due to the steep valley
walls and rapid flowing waters. The bridge is essential to the school kids at Oak Grove Middle
and Elementary Schools, local residents, fire and emergency services and commuters alike, as
the next closest crossing of Nine Mile Creek is at West Old Shakopee Road.
Existing conditions (and why it is safe to use this bridge)
City Bridge inspectors inspect the bridge on an annual basis. They look at the bearings,
concrete deck, sidewalk, railings, structural steel, expansion joints and everything that can
be viewed without a snooper rig. Since the Bridge is "fracture critical," the state inspects
the structural steel and field welds with a snooper rig that can reach the entire underside of
the bridge from the west bound outside lane. MnDOT inspections were on a five-year cycle until
Governor Pawlenty changed "fracture critical" bridge inspections to two years, state-wide.
The inspection records are used by engineers to determine when maintenance is needed and track
the bridge's condition. The abutment bearings, concrete deck, expansion joints, and approach
panels all show signs of deterioration. The Cor-Ten steel is showing some signs of accelerated
corrosion due to water and salt leaking through the expansion joints. Silt continually covers
one of the pedestal bearings. None of these items are considered critical, at this time.
Engineers from the State, City and Consultant have reviewed these items and concur that this is
timely maintenance that will preserve and extend the life of this important transportation
link. The City has been planning the work for several years, and budgeting for the work began
in 2006.
Other bridge facts:
-
The bridge carries an average of 11,000 vehicles per day.
-
The main span is 110 feet, total length is 209 feet, and the driving lanes are 46 feet from
curb to curb.
-
There is an integral sidewalk on the north side, and an adjacent pedestrian bridge was
constructed in 1991, with a similar style to complement the original bridge.
-
The bridge has a sufficiency rating of 65.4, which is a composite number of various
structural member ratings. A rating below 80 allows the City to apply for State Aid Funding
for bridge rehabilitation.
-
Due to the steep slopes and vertical curve in the roadway, the bridge does not meet current
state road design criteria, thus it is also designated "functionally obsolete." This
designation does not make the bridge unsafe, and is not a designation of structural
deficiency.
-
Engineer's estimate the rehabilitation/construction will cost approximately $300,000. For
comparison, based on 2008 dollars, replacing the bridge is estimated at $4 to $5 million
dollars.
For more information, contact:
Steve Segar, Civil Engineer
1700 W. 98th Street
PH: 952-563-4533, FAX: 952-563-4868
E-mail: ssegar@ci.bloomington.mn.us
Streets HOME |
Current projects |
PMP |
Specifications
|
