Collapse of I-35W Highway Bridge Minneapolis, Minnesota ...

1 HighwayCollapse of I-35W Highway BridgeMinneapolis, MinnesotaAugust 1, 2007 ACCIDENT REPORTNTSB/HAR-08/03PB2008-916203 NationalTransportationSafety Boar dNationalTr ansportationSafety Bo ar d490 L Enfant Plaza, , 20594 Highway Accident ReportCollapse of I-35W Highway BridgeMinneapolis, MinnesotaAugust 1, 2007490 L Enfant Plaza, , 20594 NTSB/HAR-08/03PB2008-916203 Notation 7975C November 14, 2008 The national transportation safety board is an independent Federal agency dedicated to promoting aviation, railroad, Highway , marine, pipeline, and hazardous materials safety . Established in 1967, the agency is mandated by Congress through the Independent safety board Act of 1974 to investigate transportation accidents, determine the probable causes of the accidents, issue safety recommendations, study transportation safety issues, and evaluate the safety effectiveness of government agencies involved in transportation .

2 The safety board makes public its actions and decisions through accident reports, safety studies, special investigation reports, safety recommendations, and statistical publications are available in their entirety on the Web at < >. Other information about available publications also may be obtained from the Web site or by contacting: national transportation safety BoardRecords Management Division, CIO-40490 L Enfant Plaza, , 20594(800) 877-6799 or (202) 314-6551 safety board publications may be purchased, by individual copy or by subscription, from the national Technical Information Service. To purchase this publication, order report number PB2008-916203 from: national Technical Information Service5285 Port Royal RoadSpringfield, Virginia 22161(800) 553-6847 or (703) 605-6000 The Independent safety board Act, as codified at 49 Section 1154(b), precludes the admission into evidence or use of board reports related to an incident or accident in a civil action for damages resulting from a matter mentioned in the transportation safety board .

3 2008. Collapse of I-35W Highway Bridge , Minneapolis, Minnesota , August 1, 2007. Highway Accident Report NTSB/HAR-08/03. Washington, : About 6:05 central daylight time on Wednesday, August 1, 2007, the eight-lane, 1,907-foot-long I-35W Highway Bridge over the Mississippi River in Minneapolis, Minnesota , experienced a catastrophic failure in the main span of the deck truss. As a result, 1,000 feet of the deck truss collapsed, with about 456 feet of the main span falling 108 feet into the 15-foot-deep river. A total of 111 vehicles were on the portion of the Bridge that collapsed. Of these, 17 were recovered from the water. As a result of the Bridge Collapse , 13 people died, and 145 people were injured. On the day of the Collapse , roadway work was underway on the I-35W Bridge , and four of the eight travel lanes (two outside lanes northbound and two inside lanes southbound) were closed to traffic.

4 In the early afternoon, construction equipment and construction aggregates (sand and gravel for making concrete) were delivered and positioned in the two closed inside southbound lanes. The equipment and aggregates, which were being staged for a concrete pour of the southbound lanes that was to begin about 7:00 , were positioned toward the south end of the center section of the deck truss portion of the Bridge and were in place by about 2:30 About 6:05 , a motion-activated surveillance video camera at the Lower St. Anthony Falls Lock and Dam, just west of the I-35W Bridge , recorded a portion of the Collapse sequence. The video showed the Bridge center span separating from the rest of the Bridge and falling into the safety issues identified in this investigation include insufficient Bridge design firm quality control procedures for designing bridges, and insufficient Federal and State procedures for reviewing and approving Bridge design plans and calculations; lack of guidance for Bridge owners with regard to the placement of construction loads on bridges during repair or maintenance activities; exclusion of gusset plates in Bridge load rating guidance; lack of inspection guidance for conditions of gusset plate distortion; and inadequate use of technologies for accurately assessing the condition of gusset plates on deck truss bridges.

5 As a result of this accident investigation, the safety board makes recommendations to the Federal Highway Administration (FHWA) and the American Association of State Highway and transportation Officials. One safety recommendation resulting from this investigation was issued to the FHWA in January transportation safety BoardHIGHWAYA ccident ReportiiiCo n t e n t sGlossary of Bridge -Related Terms as Used in This Report ..viExecutive Summary ..xiiiFactual Information ..1 Accident Synopsis ..1 The Accident ..1 Emergency Response ..3 Initial Response ..3 Incident Command ..4 Injuries ..5 Accident Location ..5 Bridge Description ..5 General ..5 Deck Truss Portion ..9 Construction of Deck Truss ..12 Study of Collapse Video ..14 Damages ..16 Approach Spans.

6 16 Deck Truss Spans ..16 Piers and Bearings ..21 Recovery of Structure ..21 Bridge Renovations and Modifications ..221977 Renovation: Increased Deck Thickness ..231998 Renovation: Median Barrier, Traffic Railings, and Anti-Icing System ..232007 Repair and Renovation: Repaving ..24 Staging of Construction Materials on Bridge Deck ..24 Bridge Traffic and Construction Loading at Time of Collapse ..28Mn/DOT Policies Regarding Construction Loads on Bridges ..28 Bridge Load Rating and Posting ..33Mn/DOT Draft Bridge Rating Manual ..36 Load Ratings for I-35W Bridge ..38 Bridge Posting ..39 Bridge Rating and Load Posting Report, 1979 ..39 Bridge Rating and Load Posting Report, 1995 ..40 FHWA Assessment of Load Rating Records for I-35W Bridge ..42 Federal Bridge Inspection Requirements.

7 44 State Inspections and Inspection Reporting ..45 Inspection Results and Condition Ratings for I-35W Bridge ..47 Rust and Corrosion ..52Mn/DOT Underwater Bridge Inspection ..53 ContentsNational transportation safety BoardHIGHWAYA ccident ReportivWashout Hole Underneath Bridge ..53 Other Repairs ..53 Fatigue Cracking in Minnesota Bridges ..54 Lafayette Bridge ..54 Dresbach Bridge ..54 Dartmouth Bridge ..55 Lexington Bridge ..55 Hastings Bridge ..55 Oar Dock Bridge ..55 Preexisting Fatigue Cracking in I-35W Bridge ..56 University of Minnesota Fatigue Assessment of I-35W Bridge ..57 URS Corporation Inspections and Reports ..58 Bowed Gusset Plates on I-35W Bridge ..61 Examination of Deck Truss Fracture Areas ..64 South Fracture Area, Main Trusses ..64 South Fracture Area, Deck and Stringers.

8 69 South Fracture Area, Floor Trusses and Braces ..70 North Fracture Area, Main Trusses ..71 North Fracture Area, Deck and Stringers ..74 Tests and Research ..74 Preexisting Features of Structural Components ..74I-35W Bridge Gusset Plate Adequacy Analysis ..75 Analysis of Other Aspects of I-35W Bridge Design ..78 Materials Testing ..79 Finite Element Modeling of I-35W Bridge ..80 Design History of I-35W Bridge ..87 Evolution of Design ..88 Initial Design and Preliminary Engineering Report, October 1962 April 1963 ..89 Preliminary Design, April 1963 March 1964 ..90 Final Design, March 1964 March 1965 ..91 Other Information ..92Mn/DOT Postaccident Actions ..92 Deficient Gusset Plates on Other Minnesota Bridges ..93 Deficient Gusset Plates on Ohio Bridges ..95 Guidance and Training for Inspecting Gusset Plates.

9 97 FHWA AASHTO Joint Study of Gusset Plates ..101 Bridge Design Firm Process for Design and Design Review ..102Mn/DOT Bridge Design Review Process ..108 FHWA Bridge Design Review Process ..110 Design Review Processes in Other States ..112 Examples of Bridge Design Errors ..114Mn/DOT Certification of Bridge Inspectors ..116 Minnesota Emergency Preparedness and Lessons Learned ..117 ContentsContentsNational transportation safety BoardHIGHWAYA ccident ReportvAnalysis ..119 Collapse Sequence ..119 Other Possible Collapse Scenarios Considered ..123 Corrosion Damage in Gusset Plates at L11 Nodes ..123 Fracture of Floor Truss ..125 Preexisting Cracking ..125 Temperature Effects ..126 Pier Movement ..126 Emergency Response ..127 Design of the Main Truss Gusset Plates.

10 127 Origin of the Inadequate Gusset Plates ..129 Materials Substitution ..129 Design Calculations ..129 Design Quality Control ..131 FHWA, Mn/DOT, and Other State DOTs ..132 Bridge Load Rating ..133 Effect of Added Loads Over Time ..136 Guidance for Allowing Construction Loads on Bridges ..138 Inspections of I-35W Bridge ..140 Condition Rating ..141 Gusset Plate Corrosion ..142 Gusset Plate Bridges for Gusset Plate Adequacy ..145 Corrosion on Gusset Plates ..145 Distortion of Gusset Plates ..146 Guidance for Inspecting Gusset Plates ..147 Training for Bridge Inspectors ..147 Conclusions ..149 Findings ..149 Probable Cause ..152 Recommendations ..153 New Recommendations ..153 Previously Issued Recommendation Resulting From This Accident Investigation ..155 Appendixes A: Investigation.