I-35W Mississippi River bridge

Mississippi River Bridge
Bridge 9340 (1964–2007)
Coordinates	44°58′44″N 93°14′42″W
Carries	8 lanes of I-35W
Crosses	Mississippi River
Locale	Minneapolis, Minnesota, U.S.
Maintained by	Minnesota Department of Transportation (Mn/DOT)
ID number	9340
Characteristics
Design	Truss arch bridge (Deck-arch truss bridge)
Total length	1,907 ft (581.3 m)
Width	113.3 ft (34.5 m)
Height	115 ft (35.1 m)
Longest span	456 ft (139 m)
Clearance below	64 ft (19.5 m)
History
Construction start	1964
Opened	November 1967
Closed	August 1, 2007
Statistics
Daily traffic	140,000
Location

The I-35W Mississippi River bridge (officially known simply as 'Bridge 9340') was an eight-lane, 1,907 feet (581 m) steel truss arch bridge that carried Interstate 35W across the Mississippi River in Minneapolis, Minnesota, United States. Completed in 1967 and maintained by the Minnesota Department of Transportation (Mn/DOT), the bridge was Minnesota's fifth–busiest, carrying 140,000 vehicles daily.

At 6:05 pm on Wednesday, August 1 2007, during the evening rush hour, the main spans of the bridge collapsed, falling into the river and its banks. Thirteen people died and approximately one hundred more were injured. Immediately after the collapse help came from mutual aid in the seven-county metropolitan area and a multitude of civilians, hospitals, volunteers and agencies. City and county employees managed the rescue using post–9/11 techniques and technology that may have saved lives. As of early 2008, the NTSB has not reached a determination of probable cause for the collapse, but has identified a possible design error from when the bridge was originally built, which may have caused or contributed to the failure.

President of the United States George W. Bush and First Lady Laura Bush, the Secretary of Transportation, Minnesota's United States senators and representatives, and the media traveled to the wreckage during the rescue and recovery. The Federal Government provided funds to help with the costs associated with the collapse and the US SBA offered low-interest loans for those small businesses affected by the collapse .

Within a few days of the collapse, the Minnesota Department of Transportation began planning a replacement bridge, which was subsequently named the St. Anthony Falls (35W) Bridge.

Location

Map showing bridge location in red.

Located in Minneapolis, the county seat of Hennepin County, Minnesota, this north-south bridge connected the Minneapolis neighborhoods of Downtown East and Marcy-Holmes.

The north abutment of the bridge was northwest of the University of Minnesota East Bank campus. The south abutment was northeast of the Metrodome. Along with the Plymouth Avenue Bridge, the I-35W bridge bounded the "Mississippi Mile" riverfront parkland.

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

This section of the river is crowded with structures. Immediately upstream is the Lower Saint Anthony Falls lock and dam. The first bridge upstream is the Stone Arch Bridge built for rail transport, preserved in 1994 as a national historic civil engineering landmark and now carrying pedestrians and cyclists between downtown Minneapolis and the university. Downstream and even closer is the 10th Avenue Bridge, once known as the Cedar Avenue Bridge.

The bridge was one of the two major river crossings of I-35W in Minnesota, (the western branch of Interstate 35 through the Minneapolis-Saint Paul metropolitan area). The other major bridge is the I-35W Minnesota River bridge located 15 miles (24 km) to the south over the Minnesota River.

Site history

The I-35W Mississippi River bridge was located in the area where Minneapolis began, located just downstream from Saint Anthony Falls, which is the only natural waterfall in the Upper Mississippi River. Completed in 1956, the lower Saint Anthony Falls dam is a gravity type hydro-electric dam 60 feet (18 m) in height. In November of 1987 the Saint Anthony Lower Hydro-Electric Plant experienced an undermining failure and on August 19, 1988 the facility was razed; it had been very near the north bank foundation pier of the I-35W bridge.

The area of the bridge's south abutment was a site of industrial chemical pollution. For 90 years prior to the bridge's construction, Minnegasco's predecessor, Minneapolis Gas Works, operated a coal-to-gas processing plant on a 20-acre (8 ha) tract on the south bank of the river at the later site of the bridge. Minnegasco, which became part of CenterPoint Energy, demolished the plant in the 1960s, since the wide availability of natural gas made the coal-to-gas processing plant obsolete. Half the site was sold to Continental Oil Company (Conoco), which stored and processed petroleum products on the site for 20 years.

The tract's long-term industrial use effectively resulted in a toxic-waste dump below the bridge. The legal wrangling over the bill for the riverfront cleanup led to a 1991 lawsuit. 15,000 tons (13,600 t) of contaminated soil were removed from below the bridge, ground up with wood chips and burned as a fuel additive for a power plant between 1993 and 1998 at a cost of US$30 million. No causal relationship has been proven between the prior use and subsequent bridge failure.

Design and construction

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 (the latter having since gone out of business), with Industrial Construction Company building the steel trusses and deck. Construction began in 1964 and the bridge opened to traffic in 1967.

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

In its entirety, the bridge was over 1,900 feet (580 m) long. It consisted of fourteen spans: five south approach spans, three main spans, and six north approach spans. The three main spans were of deck truss construction while all but two of the approach spans were steel multi-girder construction with the remaining two approach spans being concrete slab construction. The bridge had no piers built into the river bed; instead, the center span of the bridge consisted of a single 458-foot (140 m) steel arched truss over the 390-foot (119 m) wide navigation 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. 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. 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. 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. 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. The roadway deck was approximately 115 feet (35 m) above the water level.

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. When the bridge fell, it was still the most recent river crossing built on a new site in Minneapolis. After the building boom ebbed during the 1970s, infrastructure management shifted toward inspection and maintenance.

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 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. 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. The system came into operation in 2000. It has been raised as a possibility that the potassium acetate may have contributed to the collapse of the 35W bridge.

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. 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. "Structurally deficient" is a classification term which does not in itself indicate a lack of safety. Approximately 75,000 other U.S. bridges had this classification in 2007.

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 supports 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.

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. Problems were noted in two subsequent inspection reports. The inspection carried out June 15, 2006 found problems of cracking and fatigue. On August 2, 2007, Governor Pawlenty stated that the bridge was scheduled to be replaced in 2020. The federal National Bridge Inventory database of inspection records show that 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. A score below 80 indicates that some rehabilitation may be needed, while a score of 50 or less shows that replacement may be in order. This measure includes safety elements (such as structural integrity) and factors in elements such as the bridge's size with respect to its current traffic. The I-35W bridge was given a rating of 50 in the year 2005. Out of 104,348 heavily used bridge structures (those with more than 10,000 vehicles traveling on them per day), only 4,227, or 4%, scored below 50, according to an analysis of federal records by MSNBC. Although, on a separate measure, the I-35W bridge was rated "structurally deficient," it was deemed to have met "minimum tolerable limits to be left in place as it is."

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.

The construction taking place for the few weeks prior to the collapse was minor and cosmetic, focusing on replacing lighting, concrete and guard rails and some work on joints. In the weeks before August, Mn/DOT's contractor, Progressive Contractors, Inc., conducted repairs on the surface of the bridge and, shortly before the incident, announced that it would reduce traffic flow on the bridge to one lane in each direction during the late evenings of July 31 and August 1 to accommodate construction. Progressive Contractors, Inc., was an experienced bridge and deck repair contractor that had previous experience working on the I-35W bridge. At the time of the collapse, four of the eight lanes were closed for resurfacing, and there were 575,000 pounds (261,000 kg) of construction supplies and equipment on the bridge.

Collapse

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

At 6:05 p.m. CDT on 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. Approximately 100 vehicles were involved, sending their occupants and 18 [1] construction workers up to 115 feet (35 m) down to the river or onto its banks. Northern sections fell into a rail yard, landing on three unoccupied and stationary freight train cars.

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. 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.

Mayor R.T. Rybak and Governor Tim Pawlenty declared a state of emergency for the city of Minneapolis and for the state of Minnesota on 2007-08-02. Rybak's declaration was approved and extended indefinitely by the Minneapolis City Council the next day. As of the morning following the collapse, according to White House Press Secretary Tony Snow, Minnesota had not requested a federal disaster declaration. President Bush pledged support during a visit to the site on 2007-08-04 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. Local authorities were assisted by the Federal Bureau of Investigation (FBI) evidence team, and by United States Navy divers who began arriving on 2007-08-05.

Victims

Collapsed bridge the evening of the collapse, looking south.

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 Sara Lee semi-truck, whose driver's body was later pulled from the cab. When fire crews arrived they had to route hoses from several blocks away.

A school bus carrying 60 children from Waite House Neighborhood Center Day Camp ended up resting precariously against the guardrail of the collapsed structure, and also near the burning semi-trailer truck. They were returning from a field trip to a water park. 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.

Thirteen deaths were attributed to the collapse. The victims, eight males and five females and aged 22 months to 60 years, were all Minnesota residents. Within 2 hours, 50 people were transported to hospitals, some in trucks when ambulances were in short supply. Triage centers at the ends of the bridge routed patients to area hospitals; 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, five at HCMC and four or five at North Memorial Medical Center in Robbinsdale, Minnesota. During the first 40 hours, 11 area hospitals treated 98 victims.

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. Minnesotans held a minute of silence during National Night Out, on August 7, 2007 at 6:05 pm. On 2007-08-08, 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. The flags are at half-staff indefinitely. Gold Medal Park near the Guthrie Theater was a gathering place for those who wished to leave flowers or remembrances for those who died. During an address to the city council on 2007-08-15, Rybak remembered each of the victims and "the details of their lives."

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.

In November 2007, District Judge Herbert Lefler of Hennepin County denied a request for access to complete information, which the state transportation department received from lawyers representing the victims. This information includes "data created and received in the course of the investigation of the I-35W bridge collapse".

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.

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. Emergency personnel arrived in six minutes 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.

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.

The Minneapolis Fire Department (MFD) created the National Incident Management System command center in the parking lot of the American Red Cross and an adjacent printing company 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. The city provided 75 firefighters and 75 law enforcement units.

Rescue of victims stranded on the bridge was complete in three hours. "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. 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. Their rapid response time is also credited to the Minnesota and United States Department of Homeland Security (DHS) investment in 800MHz mobile radio communications that was operating in Minneapolis and three of the responding counties, the city of Minneapolis collapsed-structures rescue and dive team, and the Emergency Operations Center established at 6:20 p.m. in Minneapolis City Hall.

Recovery

File:I-35W-US Navy divers-Minneapolis-20070807.jpg

United States Navy divers arriving from the Naval Amphibious Base Little Creek

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). 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 use an unmanned submarine with a robotic arm, camera, and lights to look for any evidence that might help with the investigation; they had to abandon this plan after it was found to be too big to maneuver in the debris field and cloudy water. The FBI attempted to use a shoebox-sized sub that only had lights and a camera; its effectiveness is unknown. 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."

Helicopter and airboat on the 10th Avenue Bridge

Seventy-five local, state and federal agencies 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. 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.

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

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. 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.

Leading the rebuilding effort, United States Secretary of Transportation Mary Peters visited Minneapolis four times as of 2007-08-22. Left to right, Col. Michael Chesney, Peters, 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 blow torches to remove parts of the bridge deck, beams and girders hoping to improve access for the divers. 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. 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 where owners could claim their vehicles. 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.

From USDOT, Minnesota received US$5 million Peters announced on the day following the collapse. 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". 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. 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. 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". "On behalf of Minnesota, we are grateful for all of this help," Pawlenty said.

Investigation

FBI evidence team and Hennepin County sheriffs lowering sonar

The National Transportation Safety Board immediately began a comprehensive investigation, which could take up to eighteen months to complete. One week after the collapse, debris and vehicles were just beginning to be moved to further the process of recovering victims. 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."

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. However, his original software is no longer available. The Federal Highway Administration (FHWA) is building a computer model of the bridge at the Turner Fairbank Highway Research Center in McLean, Virginia. NTSB investigators were particularly interested in learning why a part of the bridge's southern end shifted eastward as it collapsed. The NTSB quickly ruled that out as a starting point, and shifted its focus to the north end of the structure.

Officials with DHS said there was no indication that terrorism was involved. FHWA advised states to inspect the 700 U.S. bridges of similar construction 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. 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. This flaw was first discovered by an independent consulting firm hired by MnDOT to investigate the cause of the collapse. The firm, Wiss, Janney, Elstner, Associates, Inc., quickly informed MnDOT and the NTSB of the potential flaw so that they could focus their investigations accordingly. 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." Within days, bridge inspections were stepped up throughout the United States.

On January 15, 2008 the National Transportation Safety Board announced they had determined that the bridge had a design error. The NTSB reported that the designers had specified steel gusset plates connecting several girders which were undersized and inadequate to support the intended load of the bridge. This assertion was made based on on interim report which calculated the Demand to Capacity ratio for the gusset plates . The U10 and L11 plates were judged by the report to have inadequate safety margins. MnDot inspectors had been tracking corrosion in the L11 plate. The bridge carried even more weight over the decades due to a thicker concrete deck and larger barriers. The NTSB recommended that similar bridge designs be reviewed for this problem..

"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."

A separate 2006 report for the Minnesota DOT had noted increased traffic volume, and increased maximum vehicle weight.

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.

Effect of collapse on business and traffic

Closure sign on Interstate 35W

The collapse of the bridge affected rail, river, road and air transit. Pool 1, created by Ford Dam, was closed to river navigation between mile markers 847 and 854.5. A rail spur owned by the Burlington Northern Santa Fe Railway and switched by the Minnesota Commercial Railway was blocked by the collapse. The Grand Rounds National Scenic Byway bike path is currently 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 radius of the rescue and recovery.

Day of the collapse

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.

Small businesses in Anoka, Carver, Dakota, Hennepin, Ramsey, Scott, Sherburne and Wright 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. The agency's disaster declaration for Hennepin and contiguous counties came two days after Pawlenty's request to the SBA on 2007-08-20. 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. 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.

Seventy percent of the traffic served by the bridge was downtown-bound. 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 Interstate 694, Interstate 494, and Interstate 35E. The Tenth Avenue bridge was closed the day after the collapse at the speculation of the bridge being flooded with pedestrians wanting to get a closer look at the site. The bridge was reopened nearly a month later.

Extra Metro Transit buses were added from park-and-ride locations in the northern suburbs during the rush hours. 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. On August 8, cameras, motion detectors, and other technology were added to the site around the bridge to ward off intruders, whom officials claimed were hindering the investigation of the cause of the collapse.

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 canceling the game could hamper rescue and recovery efforts, since a cancellation 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. The collapse will affect logistics and planning for the 2008 Republican National Convention being held at Saint Paul's Xcel Energy Center.

Laura Bush added plans to visit the bridge site and the city command center. On 2007-08-03 she was to visit Minneapolis for a Republican National Committee meeting and speak at a Helping Americas Youth conference at the university's Saint Paul campus.

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

The collapse was of interest to national and international news organizations. 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. 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.

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-AM (1500), 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.

On PBS television on 2007-08-15, Peters said USDOT was opposed to raising the 18.4 cent federal gasoline tax, skeptical that the tax was the right vehicle for an upgrade of the nation's infrastructure. She offered sympathy and criticized communities by saying that 10 to 20 percent of transportation spending is on projects like restoring lighthouses, museums, bike paths, and trails, rather than on infrastructure.

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. About two weeks later, Pawlenty requested major disaster designation on 2007-08-20. 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." 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, 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. He estimated the cost of the collapse to the state at US$400,000 to US$1 million per day.

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. 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. Pawlenty planned to ask that the date restriction and monetary cap be lifted. 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.

Replacement bridge

Main article: St. Anthony Falls (35W) Bridge

The replacement of the collapsed I-35W Mississippi River bridge will cross the Mississippi River at the same location as the original bridge, and will carry north-south traffic on Interstate Highway 35W. It is under construction on an accelerated schedule, due to the highway's function as a vital link for carrying commuters and truck freight. Mn/DOT announced on September 19, 2007 that Flatiron Constructors and Manson Construction Company will build the replacement bridge for USD $234 million, to be completed no later than December 24, 2008.

Gallery

• 
  View from pedestrian bridge looking west, 35W bridge in Mississippi River
• 
  Fire department survey on the day of the collapse
• 
  Green girders from collapsed I-35W bridge protrude up from Mississippi River.
• 
  View from remaining bridge approach.
• 
  The bridge before and after, from the same vantage point.
• 
  Rescue floodlights on the 10th Avenue Bridge.
• 
  Collapsed bridge and 10th Avenue bridge seen from the air
• 
  Recovery on 2007-08-26 seen from inside the Guthrie Theater
• 
  Vehicles on fire. Minneapolis Fire Department on West River Parkway
• 
  Rescue boats, Saint Anthony Falls lock and dam
• 
  Rescue boats on the riverbank
• 
  Southwest pier and gusset plate in 1996
• 
  Collapsed bridge taken on September 1, 2007 from the 10th Avenue Bridge. Note that much of the concrete decking, and some of the support structure had been removed by this time.
• 
  Pieces of collapsed 35W bridge laid out on "Bohemian Flats" area downriver from the bridge. Taken on September 1,2007 from the pedestrian Northern Pacific Bridge Number 9.
• 
  Taken on September 13th from the 10th Avenue Bridge.

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)

Further reading

• Cavanaugh, Patricia (2006). "Politics and Freeways: Building the Twin Cities Interstate System" (PDF). University of Minnesota. {{cite web}}: Unknown parameter |month= ignored (help)
• Costello, Mary Charlotte (2002). Climbing the Mississippi River Bridge by Bridge, Volume Two: Minnesota. Cambridge, MN: Adventure Publications. ISBN 0–9644518–2-4. {{cite book}}: Cite has empty unknown parameter: |coauthors= (help)
• "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. Retrieved 2007-08-24.
• "Timeline Of Bridge Collapse". Internet Broadcasting via WNBC (wnbc.com), NBC Universal, Inc (General Electric Company, Vivendi S.A.). 2007-08-01, last modified 2007-08-03. Retrieved 2007-09-02. {{cite web}}: Check date values in: |date= (help)

External links

• 35W Bridge Collapse is a hub for 35W bridge collapse information

• MSP Bridges: Historic I-35W Mississippi River Crossing
• Scientific perspectives on the collapse — from the Science Museum of Minnesota
• Template:Geolinks-US-streetscale
• Bridge Skin Could Reveal Cracks And Corrosion Beneath — sciencedaily.com, August 9, 2007.
• Minnesota bridge safety legal resources from LawMoose
• Minneapolis Bridge Collapse & Citizen Journalism
• Minnesota Historical Society: 35W Bridge Resources
• BigEyeInTheSky.com — featuring a 360-degree aerial panorama of the collapsed bridge and surrounding area
• "Minneapolis Bridge Collapse (photos)". U.S. Department of Defense Imagery Server. Retrieved 2007-08-22.
• 3rd Party I-35W Bridge Collapse Failure Analysis Unofficial discussion and analysis based on publicly-available photographs of the bridge.
• U.S. Bridge Information - New AASHTO Bridge Information Web Site