I-35W Mississippi River bridge

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Mississippi River Bridge
Bridge 9340 (1964–2007)
Carries	8 lanes of I-35W
Crosses	Mississippi River
Locale	Minneapolis, MN
Maintained by	Minnesota DOT
ID number	9340
Design	Truss arch bridge
Longest span	456 ft (139 m)[1]
Total length	1,907 ft (581.3 m)
Width	113.3 ft (34.5 m)
Height	115 ft (35.1 m)
Clearance below	64 ft (19.5 m)
AADT	140,000[2]
Beginning date of construction	1964[3]
Opening date	November 1967
Destruction date	August 1, 2007
Coordinates	44°58′44″N 93°14′42″W / 44.97889°N 93.245°W / 44.97889; -93.245Coordinates: 44°58′44″N 93°14′42″W / 44.97889°N 93.245°W / 44.97889; -93.245

The I-35W Mississippi River bridge (officially known simply as Bridge 9340) was an eight-lane steel truss arch bridge that carried Interstate 35W across the Mississippi River in Minneapolis, Minnesota, United States. The bridge was completed in 1967, and its maintenance was performed by the Minnesota Department of Transportation. The bridge was Minnesota's fifth–busiest,^[4][5] carrying 140,000 vehicles daily.^[2]

The bridge catastrophically failed during the evening rush hour on August 1, 2007, collapsing to the river and riverbanks beneath. Thirteen people were killed and 145 were injured. Help came immediately after the collapse from mutual aid in the seven-county Minneapolis-Saint Paul metropolitan area and emergency response personnel, charities, and volunteers. City and county employees managed the rescue using post-9/11 techniques and technology that may have saved lives.^[6][7][8]

Within a few days of the collapse, the Minnesota Department of Transportation planned a replacement bridge, the I-35W Saint Anthony Falls Bridge, which opened on September 18, 2008.^[9][10]

The NTSB has cited a design flaw as the likely cause of the collapse, and asserted that additional weight on the bridge at the time of the collapse contributed to the failure.^[11]

[edit] Location and site history

Bridge location in red

Located in Minneapolis, Minnesota's largest city, the bridge connected the Minneapolis neighborhoods of Downtown East and Marcy-Holmes. The south abutment was northeast of the Metrodome, and the north abutment was northwest of the University of Minnesota East Bank campus. The bridge was the southeastern boundary of the "Mississippi Mile" downtown riverfront parkland.^[12]

Downstream is the 10th Avenue Bridge, once known as the Cedar Avenue Bridge. Immediately upstream is the lock and dam at Saint Anthony Falls, where Minneapolis began. The first bridge upstream is the historic Stone Arch Bridge, built for the Great Northern Railway and now used for bicycle and pedestrian traffic.^[13]

The north foundation pier of the bridge was near a hydroelectric plant, razed in 1988. The south abutment was in an area polluted by a coal-to-gas processing plant^{[14][15][16][17]} and a facility for storing and processing petroleum products.^[15] These uses effectively created a toxic waste site under the bridge, leading to a lawsuit and the removal of the contaminated soil.^{[15][14][18][19][20]} No relationship between these prior uses and the bridge failure has been claimed.

[edit] Design and construction

Southeast Steam Plant (left), Stone Arch Bridge, I-35W bridge (right) and behind it, the 10th Avenue Bridge and the University of Minnesota in 2005

I-35W bridge south end seen from West River Parkway

I-35W bridge (center left) west of the 10th Avenue Bridge (center right), over the Mississippi River, 2004

The bridge, officially designated 'Bridge 9340', was designed by Sverdrup & Parcel to 1961 American Association of State Highway Officials (AASHO, the precursor to AASHTO) standard specifications. The construction contracts, worth in total more than US$5.2 million at the time, went to Hurcon Inc. and Industrial Construction Company,^[21] which built the steel trusses and deck. Construction began in 1964 and the bridge opened to traffic in 1967.^[22][23]

The bridge's fourteen spans extended 1,907 feet (580 m) long. The three main spans were of deck truss construction while all but two of the eleven approach spans were steel multi-girder construction, the two exceptions being concrete slab construction. The piers were not built in the navigation channel; instead, the center span of the bridge consisted of a single 458-foot (140 m) steel arched truss over the 390-foot (119 m) channel. The two support piers for the main trusses, each with two load-bearing concrete pylons at either side of the center main span, were located on opposite banks of the river.^[24][25] The center span was connected to the north and south approaches by shorter spans formed by the same main trusses. Each was 266 feet (81 m) in length, and was connected to the approach spans by a 38 foot (11.6 m) cantilever.^[22][26] The two main trusses, one on either side, ranged in depth from 60 feet (18.3 m) above their pier and concrete pylon supports, to 36 feet (11 m) at midspan on the central span and 30 feet (9 m) deep at the outer ends of the adjoining spans. At the top of the main trusses were the deck trusses, 12 feet (3.6 m) in depth and integral with the main trusses.^[23] The transverse deck beams, part of the deck truss, rested on top of the main trusses. These deck beams supported longitudinal deck stringers 27 inches (69 cm) in depth, and reinforced-concrete pavement.^[23][26] The deck was 113 ft 4 in (34.5 m) in breadth and was split longitudinally. It had transverse expansion joints at the centers and ends of each of the three main spans.^[23][27] The roadway deck was approximately 115 feet (35 m) above the water level.^[28]

Construction on the bridge began in 1964 and the structure was completed in 1967 during an era of large-scale projects related to building the Twin Cities freeway system.^[29] When the bridge fell, it was still the most recent river crossing built on a new site in Minneapolis.^[30] After the building boom ebbed during the 1970s, infrastructure management shifted toward inspection and maintenance.^[29][31]

[edit] Black ice

In February and in December 1996, the bridge was identified as the single most treacherous cold-weather spot in the Twin Cities freeway system, because of the almost frictionless thin layer of black ice which regularly forms as temperatures drop to 30s Fahrenheit (−1 °C to 4 °C) and below. The bridge's proximity to Saint Anthony Falls contributed significantly to the icing problem and the site was noted for frequent spinouts and collisions^[32][33] By January 1999, Mn/DOT began testing magnesium chloride solutions and a mixture of magnesium chloride and a corn-processing byproduct to see whether either would reduce the black ice that appeared on the bridge during the winter months.^[34] In October 1999, the state embedded temperature-activated nozzles in the bridge deck to spray the bridge with potassium acetate solution to keep the area free of winter black ice.^[35][36] The system came into operation in 2000.^[37][38] It has been raised as a possibility that the potassium acetate may have contributed to the collapse of the 35W bridge.^[39]

[edit] Maintenance and inspection

I-35W bridge (left) in 2006

Since 1993, the bridge was inspected annually by Mn/DOT, although no inspection report was completed in 2007, due to the construction work.^[21] In the years prior to the collapse, several reports cited problems with the bridge structure. In 1990, the federal government gave the I-35W bridge a rating of "structurally deficient," citing significant corrosion in its bearings. Approximately 75,000 other U.S. bridges had this classification in 2007.^[21][40]

According to a 2001 study by the civil engineering department of the University of Minnesota, cracking had been previously discovered in the cross girders at the end of the approach spans. The main trusses connected to these cross girders and resistance to motion at the connection point bearings was leading to unanticipated out-of-plane distortion of the cross girders and subsequent stress cracking. The situation was addressed prior to the study by drilling the cracks to prevent further propagation and adding support struts to the cross girder to prevent further distortion. The report also noted a concern about lack of redundancy in the main truss system, which meant the bridge had a greater risk of collapse in the event of any single structural failure. Although the report concluded that the bridge should not have any problems with fatigue cracking in the foreseeable future, the bridge instrumentation by strain gages and continuous structural health monitoring had been suggested.^[22]

The bridge seen from below in 2006

In 2005, the bridge was again rated as "structurally deficient" and in possible need of replacement, according to the U.S. Department of Transportation's National Bridge Inventory database.^[41] Problems were noted in two subsequent inspection reports.^[42][43] The inspection carried out June 15, 2006 found problems of cracking and fatigue.^[43] On August 2, 2007, Governor Pawlenty stated that the bridge was scheduled to be replaced in 2020.^[44]

The I-35W bridge ranked near the bottom of federal inspection ratings nationwide. The scale used was a "sufficiency rating" which ranges from the highest score, 100, to the lowest score, zero. In 2005 the bridge was given a rating of 50, indicating that replacement may have been in order. Out of over 100,000 heavily used bridges, only about 4% scored below 50. On a separate measure, the I-35W bridge was rated "structurally deficient," but was deemed to have met "minimum tolerable limits to be left in place as it is."^[42][43][45]

In December 2006, a steel reinforcement project was planned for the bridge. However, the project was canceled in January 2007 in favor of periodic safety inspections, after it was revealed that drilling for the retrofitting would in fact weaken the bridge. In internal Mn/DOT documents, bridge officials talked about the possibility of the bridge collapsing and worried that it might have to be condemned.^[46]

The construction taking place in the weeks prior to the collapse included joint work and replacing lighting, concrete and guard rails. At the time of the collapse, four of the eight lanes were closed for resurfacing,^{[47][48][49][50]} and there were 575,000 pounds (261,000 kg) of construction supplies and equipment on the bridge.^[51]

[edit] Collapse

Security camera images show the collapse in animation, looking north.

At 6:05 p.m. CDT on Wednesday, August 1, 2007, with rush hour bridge traffic moving slowly through the limited number of lanes, the central span of the bridge suddenly gave way, followed by the adjoining spans. The structure and deck collapsed into the river and onto the riverbanks below, the south part toppling 81 feet (25 m) eastward in the process.^[52] Approximately 100 vehicles^[53] were involved, sending their occupants and 18 ^[54] construction workers up to 115 feet (35 m)^[28] down to the river or onto its banks. Northern sections fell into a rail yard, landing on three unoccupied and stationary freight train cars.^{[55][56][57][58]}

Sequential images of the collapse were taken by an outdoor security camera located at the parking lot entrance of the control facility for the Lower Saint Anthony Falls Lock and Dam.^[59][60] The immediate aftermath of the collapse was also captured by a Mn/DOT traffic camera that was facing away from the bridge during the collapse itself.^[61]

Mayor R.T. Rybak and Governor Tim Pawlenty declared a state of emergency for the city of Minneapolis^[62] and for the state of Minnesota^[63] on August 2, 2007. Rybak's declaration was approved and extended indefinitely by the Minneapolis City Council the next day.^[64] As of the morning following the collapse, according to White House Press Secretary Tony Snow, Minnesota had not requested a federal disaster declaration.^[65] President Bush pledged support during a visit to the site on August 4 with Minnesota elected officials and announced that United States Secretary of Transportation (USDOT) Mary Peters would lead the rebuilding effort. Rybak and Pawlenty gave the president detailed requests for aid during a closed-door meeting.^[62][66] Local authorities were assisted by the Federal Bureau of Investigation (FBI) evidence team,^[67] and by United States Navy divers who began arriving on August 5, 2007.^[68]

A new bridge replacing the collapsed span opened on September 18, 2008, months ahead of schedule and under budget.

[edit] Victims

Cars that were on the bridge when it collapsed remain on the wreckage. They were numbered as part of the investigation.

Only a few of the vehicles were submerged, but many people were stranded on the collapsed sections of the bridge. Several involved vehicles caught fire, including a semi-truck, from which its driver's body was later pulled. When fire crews arrived they had to route hoses from several blocks away.^[69][70][71]

A school bus carrying 60 children ended up resting precariously against the guardrail of the collapsed structure, near the burning semi-trailer truck. The children were returning from a field trip to a water park as part of the Waite House Neighborhood Center Day Camp based out of the Phillips community.^[72] Jeremy Hernandez, a 20-year-old staff member on the bus, assisted many of the children by kicking out the rear emergency exit and escorting or carrying them to safety. One youth worker was severely injured and ten of the children had minor injuries.^[73]

Thirteen people, eight males and five females, lost their lives. They were a cross-section of ages and ethnicities, including a Somali immigrant and her two-year-old child, an immigrant from Mexico, a Ho-Chunk Indian, a young man with Down Syndrome and his mother, a construction worker, and other Minnesota residents.^[74] Triage centers at the ends of the bridge routed 50 victims to area hospitals, some in trucks, as ambulances were in short supply.^[75] Many of the injured had blunt trauma injuries. Those near the south end were taken to Hennepin County Medical Center (HCMC)—those near the north end, to the Fairview-University Medical Center and other hospitals. At least 22 children were victims. Thirteen children were treated at Children's Hospitals and Clinics of Minnesota,^[76] five at HCMC and four or five at North Memorial Medical Center in Robbinsdale, Minnesota.^[77] During the first 40 hours, 11 area hospitals treated 98 victims.^[76]

Observers at Gold Medal Park

About 1,400 people gathered for an interfaith service of healing held at St. Mark's Episcopal Cathedral on August 5, 2007 when many of the victims were still missing. Among the presenters were representatives of the Jewish, Christian, Islamic, Hindu, Native American, and Hispanic communities, police, fire and emergency responders, the governor, the mayor, a choir and several musicians.^[78] Minnesotans held a minute of silence during National Night Out, on August 7, 2007 at 6:05 pm.^[79] On August 8, 2007, the Twin Cities chapter of the American Red Cross lowered the flags of the United States, the state of Minnesota and the American Red Cross in remembrance of the victims of the tragedy.^[80] Gold Medal Park near the Guthrie Theater was a gathering place for those who wished to leave flowers or remembrances for those who died.^[81] During an address to the city council on 2007-08-15, Rybak remembered each of the victims and "the details of their lives."^[82]

Mayor R. T. Rybak surveys the collapsed bridge

The families of the deceased, the survivors, and the first responders who were directly impacted by the bridge collapse—together estimated to be at least several hundred people—did not have United States disaster assistance for individuals. Sandy Vargas, president and CEO of the Minneapolis Foundation, one of seven foundations that form Minnesota Helps, believes the Minnesota Helps Bridge Disaster Fund cannot cover the uninsured medical costs for the victims of the bridge collapse. The fund may be able to make small grants as a gesture of acknowledgment.^[83]

Pawlenty and his office, during the last week of November, announced a "$1 million plan" for the victims. State law has limits that may limit awards to below that amount. No legislative action was needed for this step. "The administration wanted approval from the Joint House-Senate Subcommittee on Claims as a sign of bipartisan support" which it received.^[84] On May 2, 2008 the state of Minnesota reached a $38 million agreement to compensate victims of the bridge collapse.^[85]

[edit] Rescue

University of Minnesota Police and Minnesota State Patrol, day of the collapse

Civilians immediately took part in the rescue efforts. Minneapolis and Hennepin County received mutual aid from neighboring cities and counties throughout the metropolitan area.^[86] Emergency personnel arrived in six minutes^[87] and responded quickly, helping people who were trapped in their vehicles. They worked in their rescue efforts through the night, but by the next morning, they had shifted their focus to the recovery of bodies, with several vehicles known to be trapped under the debris and several people still unaccounted for. Twenty divers organized by the Hennepin County Sheriff's Office (HCSO) used side-scan sonar to locate vehicles submerged in the murky water. Their efforts were hampered by debris and challenging currents. The United States Army Corps of Engineers (USACE) lowered the river level by two feet (60 cm) downriver at Ford Dam in order to allow easier access to vehicles in the water.^{[58][88][89][90]}

Ninety-three people were rescued from the collapsed bridge. Minneapolis Fire Department boats on the Mississippi River took about twenty people. The rescue lasted about three hours.^[75]

The Minneapolis Fire Department^[87] (MFD) created the National Incident Management System command center in the parking lot of the American Red Cross and an adjacent printing company^[7] on the west bank. The Minneapolis Police Department (MPD) secured the area, MFD managed the ground operations, and HCSO was in charge of the water operation.^[91] The city provided 75 firefighters and 75 law enforcement units.^[62]

Rescue of victims stranded on the bridge was complete in three hours.^[75] "We had a state bridge, in a county river, between two banks of a city. ... But we didn't have one problem with any of these issues, because we knew who was in charge of the assets," said Rocco Forte, city Emergency Preparedness Director.^[7] City, metropolitan area, county and state employees at all levels knew their roles and had practiced them since the city received FEMA emergency management training the year following 9/11.^[92] Their rapid response time is also credited to the Minnesota and United States Department of Homeland Security (DHS) investment in 800 MHz mobile radio communications that was operating in Minneapolis and three of the responding counties,^[6][93] the city of Minneapolis collapsed-structures rescue and dive team,^[62] and the Emergency Operations Center established at 6:20 p.m. in Minneapolis City Hall.^[7][87]

[edit] Recovery

United States Navy divers in the recovery operation, diving from a U.S. Army Corps of Engineers barge

Recovery of victims took over three weeks. At the request of USDOT, the Navy sent 17 divers and a five-person command and control element from their Mobile Diving and Salvage Unit (MDSU) 2 (TWO).^[68] Divers and Underwater Search Evidence Response Team from the FBI joined the response efforts on 2007-08-07 bringing with them "truck-loads" of specialized equipment including FBI-provided side-scan sonar and two submarines. Not waiting for daybreak, the Navy team was in the water at 2 a.m. The FBI teams had planned to search with an unmanned submarine, but had to abandon this plan after it was found to be too big to maneuver in the debris field and cloudy water. Minneapolis Police Captain Mike Martin stated that "The public safety divers are trained up to a level where they can kind of pick the low-hanging fruit. They can do the stuff that's easy. The bodies that are in the areas where they can sweep shore to shore, the vehicles that they can get into and search that weren't crushed. They were able to remove some of those. Now what we're looking at is the vehicles that are under the bridge deck and the structural pieces."^[94][95][96]

Helicopter and airboat on the 10th Avenue Bridge

Seventy-five local, state and federal agencies^[91] were involved in the rescue and recovery including emergency personnel and volunteers from the counties of Anoka, Carver, Dakota, Olmsted, Ramsey, Scott, Washington, Winona, Wright, St. Croix County, Wisconsin and others standing by.^[97][98][99] Federal assistance came from the United States Department of Defense, DHS, USACE and the United States Coast Guard. Adventure Divers of Minot, North Dakota is a private firm who assisted local authorities.^[97]

Local businesses donated wireless Internet, ice, drinks and meals for first responders.^[100] The Salvation Army canteens served food and water to rescue workers. The Billy Graham Evangelistic Association provided chaplains.^[101] A Mayo Clinic transport helicopter was standing by at Flying Cloud Airport.^[99] The Minnesota National Guard launched a MEDEVAC helicopter and had up to 10,000 guard members ready to help.^[91]

As of August 8, 2007, more than 500 Red Cross volunteers and staff persons counseled 2,000 people with grief, trauma, missing persons, and medical issues, and served 7,000 meals to first responders.^[80] Donations totalling US$138,368 and received during the catastrophe covered the cost of Red Cross services but about $65,000 in unexpected expenses were not covered.^[83][102]

Col. Michael Chesney, Transportation Secretary Mary Peters, Sheriff Stanek

Following the initial rescue, Mn/DOT retained Carl Bolander & Sons, an earthworks and demolition contractor of Saint Paul, Minnesota to remove the collapsed bridge and demolish the remaining spans that did not fall. Divers left the water briefly on 2007-08-18 while the company's crew used cranes, excavation drills and cutting torches to remove parts of the bridge deck, beams and girders hoping to improve access for the divers.^[103] After the last person's remains were pulled from the wreckage on 2007-08-21, the company's crews began dismantling the bridge's remnants.^[104] Crews first removed the vehicles stranded on the bridge. By 2007-08-18 80 of the 88 stranded cars and trucks had been moved to the MPD impound lot^[105] where owners could claim their vehicles.^[103][106] Then workers shifted to removing the bridge deck using cranes and excavators equipped with hoe rams to break the concrete. Structural steel was then disassembled by cranes, and the concrete piers were removed by excavators. NTSB officials have asked demolition crews to use extreme care in removing the bridge remnants in order to preserve as much of the bridge materials as possible. By the end of October 2007, the demolition operation was substantially complete, enabling construction to begin on the new I-35W bridge on November 1, 2007. Much of the bridge debris is being temporarily stored at the nearby Bohemian Flats as part of the ongoing investigation of the collapse. Federal officials plan to bring some of the bridge steel and concrete to the NTSB Material Laboratory in Washington, D.C. for analysis into determining the cause of the collapse on behalf of FHWA, Mn/DOT and Progressive Construction, Inc. NTSB also interviewed eyewitnesses.^[107]

Peters announced that USDOT had granted Minnesota US$5 million the day following the collapse.^[108] On 2007-08-10, Peters announced an additional US$5 million "for Minneapolis", or "the state", "to reimburse Minneapolis for increased transit operations to serve commuters in the wake of last week’s bridge collapse".^[109] U.S. Congress removed the US$100 million per-incident cap on emergency appropriations. The United States House of Representatives and United States Senate each voted unanimously for US$250 million in emergency funding for Minnesota that President Bush signed into law on 2007-08-06.^[110][111] On 2007-08-10 Peters announced US$50 million in immediate emergency relief. The Associated Press clarified that the US$50 million was a downpayment on the US$250 million that has yet to be approved by appropriations committees.^[111][112] Minnesota could use the immediate relief for "clean-up and recovery work, including clearing debris and re-routing traffic, as well as for design work on a new bridge".^[109] "On behalf of Minnesota, we are grateful for all of this help," Pawlenty said.^[113]

[edit] Investigation

FBI evidence team and Hennepin County sheriff's deputies lowering sonar

The National Transportation Safety Board immediately began a comprehensive investigation, which was expected to take up to eighteen months to complete.^[114][115] Immediately following the collapse Governor Tim Pawlenty and MnDOT announced that the Illinois-based engineering firm of Wiss, Janney, Elstner Associates, Inc. had also been selected to provide essential analysis that would parallel the investigation being conducted by the National Transportation Safety Board.^[116] One week after the collapse, debris and vehicles were just beginning to be moved to further the process of recovering victims. Cameras and motion detectors were added to the site around the bridge to ward off intruders, whom officials said were hindering the investigation.^[117] Hennepin County Sheriff Richard W. Stanek stated, "We are treating this as a crime scene at this point. There's no indication there was any foul play involved, [but] it's a crime scene until we can determine what was the cause of the collapse."^[118]

An employee of the NTSB had written his doctoral thesis on possible failure scenarios of this specific bridge while he was a student at the nearby University of Minnesota. That thesis, including his computer model of the bridge for failure mode analysis, is being used by the NTSB to aid in their investigation.^[57][119] The Federal Highway Administration (FHWA) is building a computer model of the bridge at the Turner Fairbank Highway Research Center in McLean, Virginia.^[107] NTSB investigators were particularly interested in learning why a part of the bridge's southern end shifted eastward as it collapsed,^[120] but soon ruled that out as a starting point, and shifted focus to the north end of the structure.^[52]

Officials with DHS said there was no indication that terrorism was involved.^[121] Although officials emphasized that the cause of the collapse had not yet been determined, Peters cautioned states to "remain mindful of the extra weight construction projects place on bridges."^[122] Within days, bridge inspections were stepped up throughout the United States.^[123]

This image, from the National Transportation Safety Board's Office of Research and Engineering, shows a fracture in a gusset plate that played a key role in the collapse of the Interstate 35W bridge. (National Transportation Safety Board photo)

FHWA advised states to inspect the 700 U.S. bridges of similar construction^[124] after a possible design flaw in the bridge was discovered, related to large steel sheets called gusset plates which were used to connect girders together in the truss structure.^[125][126] Officials expressed concern about many other bridges in the United States sharing the same design and raised questions as to why such a flaw would not have been discovered in over 40 years of inspections.^[126] This flaw was first discovered by an independent consulting firm hired by MnDOT to investigate the cause of the collapse.^[126]

On January 15, 2008 the National Transportation Safety Board announced they had determined that the bridge's design specified steel gusset plates that were undersized and inadequate to support the intended load of the bridge,^[127] a load which had increased over time.^[128] This assertion was made based on an interim report which calculated the Demand to Capacity ratio for the gusset plates.^[127] The NTSB recommended that similar bridge designs be reviewed for this problem.^{[127][129][130]}

"Although the Board's investigation is still on-going and no determination of probable cause has been reached, interim findings in the investigation have revealed a safety issue that warrants attention," said NTSB Chairman Mark V. Rosenker. "During the wreckage recovery, investigators discovered that gusset plates at eight different joint locations in the main center span were fractured. The Board, with assistance from the FHWA, conducted a thorough review of the design of the bridge, with an emphasis on the design of the gusset plates. This review discovered that the original design process of the I-35W bridge led to a serious error in sizing some of the gusset plates in the main truss."^[11]

On March 17, 2008, the NTSB announced an update on the investigation. The announcement gave updates in the areas of load capacity, design issues, computer analysis and modeling, digital image analysis, and analysis of the undersized and corroded gusset plates. The investigation revealed that photos from a June 2003 inspection of the bridge showed gusset plate bowing.^[131][132]

On November 13, 2008, the NTSB released the findings of its investigation. The primary cause was the under-sized gusset plates, at 0.5 inches (13 mm) thick. Contributing to that design or construction error was the fact that 2 inches (51 mm) of concrete were added to the road surface over the years, increasing the dead load by 20%. Also contributing was the extraordinary weight of construction equipment and material resting on the bridge just above its weakest point at the time of the collapse. That load was estimated at 578,000 pounds (262,000 kg) consisting of sand, water, and vehicles. The NTSB determined that corrosion was not a significant factor, but that inspectors did not routinely check that safety features were functional.^[133]

[edit] Effect of collapse on business, traffic, and transportation funding

Closure sign on Interstate 35W

The collapse of the bridge affected river, rail, road, bicycle and pedestrian, and air transit. Pool 1, created by Ford Dam, was closed to river navigation between mile markers 847 and 854.5.^[134][135] A rail spur switched by the Minnesota Commercial Railway was blocked by the collapse.^[136] The Grand Rounds National Scenic Byway bike path was disrupted as well as two roads, West River Parkway and 2nd Street SE. The 10th Avenue Bridge, which parallels this bridge about a block downstream, was closed to both vehicle and pedestrian traffic until August 31. The Federal Aviation Administration restricted pilots in the 3-nautical-mile (5.6 km) radius of the rescue and recovery.^[137]

Thirty-five people lost their jobs when Aggregate Industries of Leicestershire, UK, a company that delivered construction materials by barge, cut production in the area.^[138]

Day of the collapse

Small businesses in metropolitan area counties that were harmed by the bridge collapse could apply beginning 2007-08-27 for loans of up to US$1.5 million at 4% interest over up to 30 years from the U.S. Small Business Administration.^[139] The agency's disaster declaration for Hennepin and contiguous counties came two days after Pawlenty's request to the SBA on 2007-08-20.^[140] Open for business and unsure they could repay loans, owners near the collapse in some cases lost 25% or 50% of their income. Large retailers in a mall of chain stores lost about the same.^[141] As of early January 2008, at least one business closed, one announced it was closing, seven of eight SBA applications had not been approved and merchants continued to explain how they are unable to shoulder more debt.^[142]

Seventy percent of the traffic served by the bridge was downtown-bound.^[143] Mn/DOT published detour information, and made real-time traffic information available for callers to 5-1-1. The designated alternate route in the area was Trunk Highway 280, which was converted to a temporary freeway with all at-grade access points closed. Other traffic was diverted to Interstates 694, 494, and 35E. The number of lanes was increased on several of the highways by repainting traffic lines to eliminate wide shoulders, and by widening various "choke-points".

Extra Metro Transit buses were added from park-and-ride locations in the northern suburbs during the rush hours.^[144] Abandoned vehicles on I-35W and 280 were towed immediately. On August 6, I-35W was opened to local traffic at the access ramps on each side of the missing section; some on-ramps remained closed.^[145]

In the aftermath, pressure was exerted on the state legislature to increase the state fuel tax to provide adequate maintenance funding for Mn/DOT.^[146] Ultimately the tax was increased by $0.055 per gallon via an override of Governor Pawlenty's veto of the legislation.^[147]

[edit] Public events and media

Observers on the Stone Arch Bridge

The Minnesota Twins chose to play their scheduled home game against the Kansas City Royals at the Hubert H. Humphrey Metrodome just west of I-35W on the evening of the accident. Public safety officials told the team that postponing the game could hamper rescue and recovery efforts, since a postponement would send up to 25,000 people back into traffic only blocks from the collapsed bridge. Before the game, a moment of silence was held for the victims of the collapse. The Twins rescheduled their August 2 game and postponed traditional groundbreaking ceremonies for the team's forthcoming stadium also located in downtown Minneapolis.^[148]

The disaster site was used as a backdrop by many TV crews.

The collapse was of interest to national and international news organizations. On the evening of the collapse, CNN, MSNBC, and FOX News Channel stayed live with its coverage during the overnight hours, along with local stations WCCO-AM (830) and KSTP (1500),^[149] with most of the coverage in the opening hours coming via satellite from Twin Cities news operations WCCO-TV, KSTP-TV, KMSP-TV, KARE-TV and Minnesota Public Radio. National TV networks sent CBS anchor Katie Couric, NBC's Brian Williams and Matt Lauer, MSNBC's Contessa Brewer, ABC's Charlie Gibson, CNN's Soledad O'Brien and Anderson Cooper, and Fox News' Greta Van Susteren and Shepard Smith to broadcast from the Twin Cities.^[150] U.S. news organizations interested in national and local bridge safety made a record number of requests for bridge information from Investigative Reporters and Editors, an organization which maintains several databases of federal information. News media made more inquiries for National Bridge Inventory data in the first 24 hours after the Minneapolis bridge collapse than for any previous data in the past 20 years.^[151]

[edit] Disaster declarations

The Hennepin County Board of Commissioners voted on 2007-08-07 to request that Pawlenty petition President Bush to declare the city of Minneapolis and Hennepin County a major disaster area.^[152] About two weeks later, Pawlenty requested major disaster designation on 2007-08-20.^[153] In a subsequent press release for a separate disaster declaration that month, he said, "Ordinarily, preliminary damage assessments are completed before the emergency disaster declaration is requested."^[154] During a press conference and briefing with Bush at the Minneapolis/St.Paul Air Reserve Station base for the 934th Airlift Wing on Tuesday, 2007-08-21,^[155] Pawlenty estimated the total cost of emergency response at over US$8 million including Hennepin County's cost at US$7.3 million for rescue and recovery and US$1.2 million for other state agencies.^[156] He estimated the cost of the collapse to the state at US$400,000 to US$1 million per day.^[157]

That day, Bush gave an emergency rather than major disaster declaration for the state of Minnesota, allowing local and state agencies to recover costs incurred 2007-08-01 to 2007-08-15 from FEMA.^[158][157] FEMA can provide payment as required for emergency protective measures (part of FEMA Category B) at no less than 75% federal funding to Hennepin County, the designated county, up to the initial limit of US$5 million.^[159] Pawlenty planned to ask that the date restriction and monetary cap be lifted.^[157] FEMA aid can compensate the county for the saving of lives, protection of public safety and health, and lessening damage to improved property, but not for the disaster-related needs of the victims nor for removing debris and restoration of the bridge and riverfront nor many other categories of needs.^[160]

[edit] Replacement bridge

The replacement of the collapsed I-35W Mississippi River bridge crosses the Mississippi River at the same location as the original bridge, and carries north-south traffic on Interstate Highway 35W. It was constructed on an accelerated schedule, due to the highway's function as a vital link for carrying commuters and truck freight.^[161]

Mn/DOT announced on September 19, 2007 that Flatiron Constructors and Manson Construction Company would build the replacement bridge for USD $234 million.^[162]

The I-35W Saint Anthony Falls Bridge was opened to the public on September 18, 2008 at 5am.^[163]

[edit] See also

• List of crossings of the Upper Mississippi River
• List of bridge disasters
• Minnesota State Highway 280 (Mn/DOT's designated detour route for I-35W)

[edit] References

[edit] Bibliography

• Cavanaugh, Patricia (October 2006). "Politics and Freeways: Building the Twin Cities Interstate System" (PDF). University of Minnesota. http://www.cura.umn.edu/publications/Freeways.pdf. 
• Costello, Mary Charlotte (2002). Climbing the Mississippi River Bridge by Bridge, Volume Two: Minnesota. Cambridge, MN: Adventure Publications. ISBN 0–9644518–2-4. 
• "Robert T. Stafford Disaster Relief and Emergency Assistance Act, as amended, and Related Authorities" (PDF). Federal Emergency Management Agency (FEMA), U.S. Department of Homeland Security. June 2007. http://www.fema.gov/pdf/about/stafford_act.pdf. Retrieved on 2007-08-24. 
• U.S. Coast Guard Response to I-35 Bridge Collapse (PDF)

[edit] Notes

[edit] External links

Wikimedia Commons has media related to: I-35W Mississippi River Bridge

Wikinews has related news: Highway bridge in Minneapolis, Minnesota, collapses

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• Scientific perspectives on the collapse — from the Science Museum of Minnesota
• Minnesota Historical Society: 35W Bridge Resources
• "Minneapolis Bridge Collapse (photos)". U.S. Department of Defense Imagery Server. http://jccc.afis.osd.mil/images/deflink_ss.pl?Lbox=defenselink.Minneapolis_Bridge_Collapse. Retrieved on 2007-08-22. 
• U.S. Bridge Information - New AASHTO Bridge Information Web Site
• NTSB Docket Management System for Bridge Collapse Investigation Documents
• Radio breaking news and coverage (airchecks) of the 35W bridge collapse From radiotapes.com.
• OxBlue Construction Camera and time-lapse footage of reconstruction

Bridges of the Mississippi River Upstream Stone Arch Bridge I-35W Mississippi River bridge (collapsed) and I-35W Saint Anthony Falls Bridge Downstream 10th Avenue Bridge

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