The Department of Transportation and Public
Facilities has received numerous calls from residents
understandably concerned about Alaska’s bridges
in light of the media coverage of the Minneapolis I35W
tragedy. If you are allowed to drive on a public bridge
in Alaska, you can do so because it has been deemed
safe.
In the absence of a clear cause for the
Minneapolis bridge failure, the Federal Highway Administration
asked all states to inspect similar deck truss constructed
bridges in their inventory. While FHWA indicated that
Alaska has seven such bridges, actually only six remain
in use. All of these bridges will be inspected by September
1, 2007. They are:
The four bridges found on our National
Highway System or Alaska Highway System have been deemed
in good condition according to their last inspection
reports.
DOT&PF is responsible for inspecting
all state-owned and local government owned public bridges
every two years. Federally-owned bridges are inspected
by the federal government.
The DOT&PF Bridge Section inspects
half of the approximately 1,000 public bridges every
year. Here are some highlights of our bridge inspection
program:
| •
Routine Bridge Inspections |
| •
|
Inspections
are performed by two-person teams, usually led by
a licensed professional engineer from the Bridge
Design staff. |
•
|
Various equipment is
used to test specific areas that show significant
deterioration. |
•
|
Soundings are taken
at water crossings to monitor streambed elevations
and potential scour or erosion. |
•
|
Concrete decks are sounded
with a chain drag to identify damaged areas |
•
|
Observations are recorded
and necessary repair recommendations are logged.
|
| •
There are two requirements
that must be met before a bridge is eligible for
federally-funded rehabilitation or replacement.
|
•
|
Rehabilitation funding
is available if the “sufficiency rating”
is less than 80 percent. |
•
|
Replacement funding
is available if the “sufficiency rating”
is less than 50 percent. |
| •
A bridge must also be designated
as functionally obsolete or structurally
deficient. |
| •
The term “functionally obsolete”
speaks to the compatibility of the bridge
with the road surface that it serves and not the
condition of its components. In other words, a two-lane
bridge that serves a four-lane road would be an
example of a functionally obsolete bridge. |
| •A
bridge is deemed “structurally deficient”
if the condition of its deck, superstructure (girders)
or its substructure (abutments or piers) are rated
4 or less on a 0-9 scale. |
| •
The term “structurally deficient”
is really just intended to determine if a bridge
is eligible for federal bridge rehab or replacement
funds. It does not mean they are unsafe. |
| •
The Bridge Section also
performs several types of “special inspections”
each summer |
•
|
Fracture Critical Inspections |
| |
•
This is an inspection of bridge components
that are deemed so critical to the structure that
a failure of this component would likely cause a
catastrophic failure of the entire bridge. |
| |
•
Fracture critical inspections require the
inspector to visually inspect the so-called “fracture
critical member” within an arms length. |
| |
•
DOT&PF performs some of these inspections
either using our under-bridge inspection truck or
by hiring bridge inspectors with specialized climbing
skills. |
•
|
Underwater Inspections
are performed by certified diver/bridge inspector
firms hired by the department. |
| |
•
Damage Inspections are performed on affected
bridges following a major event such as flood, earthquake
or vehicular collisions. |
| •
Taking Action |
•
|
Bridge inspectors have
the authority to close a bridge immediately if they
find unsafe conditions at the structure and the
department has numerous examples in its bridge inventory
where it has done so. |
•
|
More likely, a deficient
bridge may only need to have new load limits applied
– Signs installed |
| |
•
Bridges that are adequate for legal loads
are not load posted |
| |
•
If a bridge is unsafe, it will be closed
or have severe load limits applied |
The department has also provided two FHWA
documents that are informative for motorists. You can
link to them below.
