On the 1st of August, 2007, the I-35 West Mississippi River Bridge, one of the busiest
bridges in Minneapolis, collapsed.
The bridge had been in use for 40 years, and during this time regular inspections had frequently
raised concerns about its structural integrity.
The collapse would, however, eventually be traced to a design flaw that none of these
inspections had ever noted, and which had been in place for decades before the failure
of the bridge.
In the second half of the 20th century a highway construction boom was sweeping across America.
Minnesota was no exception: throughout the 1950s, 1960s and 1970s huge amounts of manpower
and funding were poured into building the Twin Cities freeway system between Minneapolis
and Saint Paul.
The I-35 West Mississippi River Bridge (officially known as “Bridge 9340”) was a key component
in this project.
In the early 1960s the civil engineering company Sverdrup & Parcel were tasked with designing
the bridge, and after three years of construction the crossing was opened to traffic in 1967.
The I-35 West Mississippi River Bridge served a crucial role as one of three main routes
into downtown Minneapolis, a city with one of the highest population densities in the
Midwest.
By the mid-2000s the bridge was Minnesota’s third busiest, carrying an estimated 140,000
vehicles per day.
However, the bridge was not without its issues.
Decades of annual inspections at both a state and federal level noted a range of structural
problems, including rusting, warped and corroded metal plates.
As early as 1991 the Minnesota Department of Transportation labelled the bridge as “structurally
deficient”… but despite this the bridge remained open to the public.
The funding needed to completely renovate the bridge wasn’t readily available, and
though deficient, any defects were described as being within "minimum tolerable limits”
for the bridge to be left in place as it was.
Interestingly, the I-35 West Mississippi River Bridge was not unique in its rating as “structurally
deficient”.
In 2007, in fact, it was just one of 72,500 American bridges to be categorised as such.
Its 2006 inspection report concluded that “eventual replacement of the entire structure
would be preferable,” but this expensive option was deferred in favour of regular maintenance
and inspections.
On the evening of August 1st 2007, the I-35 West Mississippi River Bridge was filled with
rush hour traffic that had come to a near standstill.
At the time the bridge was undergoing general maintenance that had left 4 of its 8 lanes
closed and over 260,000 kilograms (or 260 tonnes) of construction materials resting
on the bridge itself.
Shortly after 6:00pm drivers heard a loud snap echo from one of the bridge's beams.
This was followed by a louder crash, and considerable trembling and shaking throughout the structure.
Seconds later a 300 metre (or 1,000 foot) section of the bridge's deck collapsed.
The southern sections of the bridge fell straight down, landing either in the Mississippi River
or on its banks.
Meanwhile, the northern end went crashing down into a rail yard, crushing three unoccupied
freight cars.
The impact of the fall was so great it broke the deck into multiple large pieces of steel
and concrete.
111 vehicles were caught in this collapse, with 17 of them falling into the waters of
the Mississippi River.
Others were left balancing precariously on the remaining pieces of the bridge, or ended
up lodged in the river's muddy banks.
The emergency response was rapid and massive in scale.
Immediately after the collapse calls came into the Minnesota State Patrol dispatch through
the 911 system.
By 6:07pm dispatchers had made the first call to coordinate a response, and at 6:08pm all
available emergency staff were directed to head for the I-35 West Mississippi River Bridge.
The highest priority tasks were rescuing people from the water and from their vehicles, extinguishing
vehicles that were on fire, conducting triage, and providing transport to nearby hospitals.
Civilians were some of the first to take part in the rescue effort.
Approximately 100 ordinary people participated, including pedestrians who happened to be near
the bridge, students and staff from the nearby University of Minnesota East Bank campus,
and construction workers who had been working on the bridge.
A group of medical personnel who had been completing a training exercise in a nearby
Red Cross building were also among the first on scene.
Emergency workers from near and far poured into the area to support the rescue effort.
One co-ordinator noted that, “We didn’t view it as a Minneapolis incident; it was
a city/county/state incident.”
Water craft from more than a dozen different public safety agencies arrived within an hour
of the collapse, and did everything they could to rescue those who had been caught up in
the disaster.
However, by 7:27pm it was concluded that everyone who could be saved had been saved, and the
difficult decision was made to shift the response from a rescue to a recovery operation.
In total, this recovery effort took more than three weeks.
The FBI Underwater Search and Evidence Response Team, and the US Naval Sea Systems Command
Mobile Diving and Salvage teams both leant resources and expertise to the effort.
Through their dedicated and painstaking work, victims of the disaster were removed from
the scene one by one until, on August 20th (19 days after the collapse) the last victim
was finally recovered.
His name was Gregory Jolstad, known as “Jolly” to his friends and family.
He was a member of the construction crew that had been undertaking general maintenance on
the bridge when it fell that summer's afternoon.
In total, 190 people were on or near the bridge when it collapsed.
145 people were injured and, sadly, 13 people lost their lives.
In the aftermath of the collapse, one question was on everyone’s mind: how could such a
catastrophic failure occur on a bridge that was so frequently used and so often inspected?
Within 24 hours of the accident investigators from the National Transportation Safety Board
were sent to the site to try and find an answer to this question.
This investigation included looking into the potential impacts of the weather, traffic,
and even the solvents which were used to melt ice in the winter.
The corrosion and rusting which had earned the bridge a rating of “structurally deficient”
were, at first, assumed to be contributing factors… but it eventually emerged that
these issues had not significantly contributed to the collapse.
Instead it was determined that an error in design made during the bridge’s original
construction was to blame.
Moreover, this flaw had gone unnoticed for more than 40 years – through repeated and
thorough inspections that had time and again identified multiple other issues with the
bridge.
The failure had occurred because of a flaw in a gusset plate used to support the truss
of the bridge.
This plate was found to be only half as thick as it should have been – a weakness exacerbated
by the fact that the load the bridge carried had increased over time as new road surfaces
were added.
The massive amount of construction equipment left on the bridge during maintenance works
had also contributed to the eventual failure of the plate.
Inspections had repeatedly caught other issues with the bridge, but it had at no point been
standard practice to check for design flaws like this during regular inspections.
Though the flaw had been in plain sight for decades, it had gone entirely unnoticed.
Understandably, the collapse raised concerns about other bridges, not just in Minnesota
but across the US.
As a measure to prevent similar accidents, guidelines have since been issued to ensure
that inspections catch problems with gusset plates and with bridge design more broadly.
Government officials across the nation were also compelled to increase inspections and
direct money towards improved bridge renovation and maintenance.
However, to this day, many bridges in the US are still categorised as structurally deficient,
with the funds needed to repair them simply not available.
Efforts to replace the I-35 West Mississippi River Bridge were fast-tracked, as it was
an essential piece of infrastructure for those living in Minnesota.
Within three days of the collapse, Congress had authorised around $250 million to rebuild
it.
The replacement bridge opened on the 18th of September 2008, just over one year after
the collapse.
Even though a new bridge has now been constructed, allowing day-to-day life in the city to return
to normal, the failure of the original bridge has not been forgotten.
On the 1st of August 2011, the four-year anniversary of the collapse, the 35 West Bridge Remembrance
Garden was opened to the public to commemorate victims and honour survivors of the disaster.
Inside this garden, 13 columns represent the individuals who lost their lives, ensuring
that the names and stories of the victims live on.