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Ing. Chiara Crosti: "La lezione di Minneapolis", Ispezione dei ponti IABMAS ITALIA 2015

"La lezione di Minneapolis", Ispezione dei ponti IABMAS ITALIA 2015

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Ing. Chiara Crosti: "La lezione di Minneapolis", Ispezione dei ponti IABMAS ITALIA 2015

  1. 1. MILANO, ITALY, NOVEMBER 20TH , 2015 LA LEZIONE DI MINNEAPOLIS Chiara Crosti “Sapienza” University of Rome, chiara.crosti@uniroma1.it
  2. 2. chiara.crosti@uniroma1.it
  3. 3. chiara.crosti@uniroma1.it COLLAPSE OF THE BRIDGE ON I 35-W MINNESOTA, AUGUST 1ST 2007 CASE STUDY
  4. 4. BEFORE chiara.crosti@uniroma1.it CASE STUDY
  5. 5. chiara.crosti@uniroma1.it CASE STUDY
  6. 6. The fixed bearing assemblies were located at piers 1, 3, 7, 9, 12, and 13. Expansion (sliding) bearings were used at the south and north abutments and at piers 2, 4, 10, and 11. Expansion roller bearings were used at piers 5, 6, and 8. chiara.crosti@uniroma1.it Bridge Scheme CASE STUDY
  7. 7. Roller #5
  8. 8. AUGUST 1ST, 2007 chiara.crosti@uniroma1.it CASE STUDY
  9. 9. chiara.crosti@uniroma1.it CASE STUDY
  10. 10. chiara.crosti@uniroma1.it CASE STUDY
  11. 11. chiara.crosti@uniroma1.it CASE STUDY
  12. 12. 27/10/2015 17franco.bontempi@uniroma1.it chiara.crosti@uniroma1.it CASE STUDY
  13. 13. 27/10/2015 18franco.bontempi@uniroma1.it chiara.crosti@uniroma1.it CASE STUDY Scheduled for reconstruction in 2020-25
  14. 14. chiara.crosti@uniroma1.it After this tragedy, the Federal Highway Administration (FHWA) focused its attention on all the 465 steel deck truss bridges present in the National Bridge Inventory [NTSB, 2008]. “The term “fracture critical” indicates that if one main component of a bridge fails, the entire structure could collapse. Therefore, a fracture critical bridge is a steel structure that is designed with little or no load path redundancy. Load path redundancy is a characteristic of the design that allows the bridge to redistribute load to other structural members on the bridge if any one member loses capacity. “ CASE STUDY
  15. 15. chiara.crosti@uniroma1.it FORENSIC INVESTIGATION National Transportation Safety Board, NTSB, 2008 “Collapse of I-35 W Highway Bridge, Minneapolis, Minnesota, August 1, 2007” Accident Report, NTSB/HAR 08/03 PB 2008- 916213, Washington D.C. 20594..
  16. 16. THE MAIN CAUSE: The primary cause was the under-sized gusset plates, at 0.5 inches (13 mm) thick; U10-W 5/67 [*] National Transportation Safety Board, “Collapse of I-35 W Highway Bridge, Minneapolis, Minnesota, August 1, 2007” Accident Report, NTSB/HAR 08/03 PB 2008-916213, Washington D.C. 20594. 2008. chiara.crosti@uniroma1.it FORENSIC INVESTIGATION
  17. 17. FINITE ELEMENT MODEL FOR OUTSIDE WEST GUSSET PLATE AT U10W 1977-1998 [*] National Transportation Safety Board, “Collapse of I-35 W Highway Bridge, Minneapolis, Minnesota, August 1, 2007” Accident Report, NTSB/HAR 08/03 PB 2008-916213, Washington D.C. 20594. 2008. chiara.crosti@uniroma1.it Stress contours for outside (west) gusset plate at U10W at time of bridge opening in 1967 Yield stress of 51.5 ksi FORENSIC INVESTIGATION South North
  18. 18. 2 inches (51 mm) of concrete were added to the road surface over the years, increasing the dead load by 20%; 6/67 [*] National Transportation Safety Board, “Collapse of I-35 W Highway Bridge, Minneapolis, Minnesota, August 1, 2007” Accident Report, NTSB/HAR 08/03 PB 2008-916213, Washington D.C. 20594. 2008. chiara.crosti@uniroma1.it FORENSIC INVESTIGATION THE ADDITIONARY CAUSE: 1977, Renovation: Increased Deck Thickness 1998, Renovation: Median Barrier, Traffic Railings, and Anti-Icing System 2007, Repair and Renovation: Repaving
  19. 19. FINITE ELEMENT MODEL FOR OUTSIDE WEST GUSSET PLATE AT U10W [*] National Transportation Safety Board, “Collapse of I-35 W Highway Bridge, Minneapolis, Minnesota, August 1, 2007” Accident Report, NTSB/HAR 08/03 PB 2008-916213, Washington D.C. 20594. 2008. chiara.crosti@uniroma1.it Stress contours for outside (west) gusset plate at U10W after 1977 and 1998 renovation projects Yield stress of 51.5 ksi FORENSIC INVESTIGATION South North
  20. 20. The extraordinary weight of construction equipment and material resting on the bridge just above its weakest point at the time of the collapse 7/67 [*] National Transportation Safety Board, “Collapse of I-35 W Highway Bridge, Minneapolis, Minnesota, August 1, 2007” Accident Report, NTSB/HAR 08/03 PB 2008-916213, Washington D.C. 20594. 2008. [*] U10-WNorth South chiara.crosti@uniroma1.it FORENSIC INVESTIGATION 184 380 lbf (820 kN) of gravel 198 820 lbf (884 kN) of sand 195 535 lbf (870 kN) of parked construction vehicles and personnel THE ADDITIONARY CAUSE:
  21. 21. The extraordinary weight of construction equipment and material resting on the bridge just above its weakest point at the time of the collapse 7/67 [*] National Transportation Safety Board, “Collapse of I-35 W Highway Bridge, Minneapolis, Minnesota, August 1, 2007” Accident Report, NTSB/HAR 08/03 PB 2008-916213, Washington D.C. 20594. 2008. [*] U10-WNorth South chiara.crosti@uniroma1.it FORENSIC INVESTIGATION Pier 6 184 380 lbf (820 kN) of gravel 198 820 lbf (884 kN) of sand 195 535 lbf (870 kN) of parked construction vehicles and personnel THE ADDITIONARY CAUSE:
  22. 22. FINITE ELEMENT MODEL FOR OUTSIDE WEST GUSSET PLATE AT U10W [*] National Transportation Safety Board, “Collapse of I-35 W Highway Bridge, Minneapolis, Minnesota, August 1, 2007” Accident Report, NTSB/HAR 08/03 PB 2008-916213, Washington D.C. 20594. 2008. chiara.crosti@uniroma1.it Stress contours for outside (west) gusset plate at U10W on August 1, 2007 Yield stress of 51.5 ksi FORENSIC INVESTIGATION South North
  23. 23. chiara.crosti@uniroma1.it FINITE ELEMENT MODEL FOR OUTSIDE WEST GUSSET PLATE AT U10W Stress contours for outside (west) gusset plate at U10W on August 1, 2007 Yield stress of 51.5 ksi FORENSIC INVESTIGATION
  24. 24. 8/31 12/44 chiara.crosti@uniroma1.it BRIDGE COLLAPSE
  25. 25. 8/31 14/44 chiara.crosti@uniroma1.it BRIDGE COLLAPSE
  26. 26. 8/31 15/44 chiara.crosti@uniroma1.it BRIDGE COLLAPSE
  27. 27. 8/31 16/44 chiara.crosti@uniroma1.it BRIDGE COLLAPSE
  28. 28. 8/31 17/44 chiara.crosti@uniroma1.it BRIDGE COLLAPSE
  29. 29. 8/31 18/44 chiara.crosti@uniroma1.it BRIDGE COLLAPSE
  30. 30. 8/31 19/44 chiara.crosti@uniroma1.it BRIDGE COLLAPSE
  31. 31. 8/31 20/44 chiara.crosti@uniroma1.it BRIDGE COLLAPSE
  32. 32. 8/31 21/44 chiara.crosti@uniroma1.it BRIDGE COLLAPSE
  33. 33. 8/31 21/44 chiara.crosti@uniroma1.it BRIDGE COLLAPSE
  34. 34. 8/31 22/44 chiara.crosti@uniroma1.it BRIDGE COLLAPSE
  35. 35. 8/31 23/44 chiara.crosti@uniroma1.it BRIDGE COLLAPSE
  36. 36. 8/31 24/44 chiara.crosti@uniroma1.it BRIDGE COLLAPSE
  37. 37. /31 25/44 chiara.crosti@uniroma1.it BRIDGE COLLAPSE
  38. 38. 8/31 13/44 chiara.crosti@uniroma1.it BRIDGE COLLAPSE
  39. 39. chiara.crosti@uniroma1.it FORENSIC INVESTIGATION
  40. 40. chiara.crosti@uniroma1.it THE MAIN CAUSE: FORENSIC INVESTIGATION
  41. 41. chiara.crosti@uniroma1.it Fixed Bearing Expansion Bearing Expansion Bearing Expansion Bearing THE MAIN CAUSE: FORENSIC INVESTIGATION
  42. 42. chiara.crosti@uniroma1.it Fixed Bearing Expansion Bearing Expansion Bearing THE MAIN CAUSE: Fixed Bearing FORENSIC INVESTIGATION
  43. 43. Temperature Effects The deck truss portion of the bridge was designed and constructed with a fixed bearing at pier 7 (on the north side of the river) and roller bearings at the remaining three piers (5, 6, and 8). Postcollapse examination of the roller bearing components showed the presence of roller wear marks, indicating that the deck truss was moving relative to piers 5, 6, and 8 in response to thermal contraction and expansion. This movement limited the amount of longitudinal force applied to the top of any pier On the day of the bridge collapse, the temperature had increased approximately 20º F from morning to early evening, the time of the accident. The finite element analysis incorporated this temperature increase with fixed bearings (but allowing for pier flexibility) to evaluate worst case temperature effects. The effects of a difference in temperature on the east and west trusses arising from the position of the sun were also evaluated. This analysis showed that the loads necessary to initiate the lateral shifting instability of diagonal L9/U10W increased with increasing temperature, and this result did not change when differential temperature was included, indicating that the change in temperature on the day of the accident did not play a role in initiation of the collapse. chiara.crosti@uniroma1.it OTHER POSSIBLE COLLAPSE SCENARIOS CONSIDERED FROM NTSB * [*] National Transportation Safety Board, “Collapse of I-35 W Highway Bridge, Minneapolis, Minnesota, August 1, 2007” Accident Report, NTSB/HAR 08/03 PB 2008-916213, Washington D.C. 20594. 2008. FORENSIC INVESTIGATION
  44. 44. Corrosion Damage in Gusset Plates at L11 Nodes None of the available evidence (video recording, evaluation of the fracture and deformation patterns, and finite element analysis) indicated a possible initial failure associated with the L11 nodes Fracture of Floor Truss Safety Board investigators considered the possibility that the collapse of the deck truss could have resulted from an initial pure tension or pure compression failure of a member within a floor truss. However, examination of the floor trusses reconstructed at Bohemian Flats revealed none of these types of fractures. Although a portion of a fracture in the upper chord of floor truss 10 contained brittle fracture characteristics, this fracture was consistent with bending loads applied when diagonal L9/U10E struck the lower surface of the upper chord of the floor truss, clearly a secondary event. Preexisting Cracking Neither of these cracks, however, was in an area associated with the identified area of the collapse initiation, and no evidence was found that preexisting cracking contributed to the collapse or significantly affected the collapse sequence chiara.crosti@uniroma1.it Pier Movement Postcollapse survey measurements indicated that piers 5 and 6 exhibited no settlement or displacement, but that piers 7 and 8 were tilting about 9º southward toward the river. The Safety Board evaluated the possibility that movement of one or both of these tilted piers initiated or affected the collapse. OTHER POSSIBLE COLLAPSE SCENARIOS CONSIDERED FROM NTSB * FORENSIC INVESTIGATION
  45. 45. chiara.crosti@uniroma1.it FORENSIC INVESTIGATION INSPECTION REPORTING FOR I-35W BRIDGE, 1983-2007
  46. 46. chiara.crosti@uniroma1.it INSPECTION REPORTING FOR I-35W BRIDGE, 2006 GUSSET PLATE??? FORENSIC INVESTIGATION
  47. 47. chiara.crosti@uniroma1.it FORENSIC INVESTIGATION BOWED GUSSET PLATE AT NODE U10
  48. 48. chiara.crosti@uniroma1.it FORENSIC INVESTIGATION INSPECTION REPORTING FOR I-35W BRIDGE
  49. 49. chiara.crosti@uniroma1.it FORENSIC INVESTIGATION
  50. 50. Continued gusset plate load ratings on 25 Trunk Hwy specified bridges that began back in October 2007 February 2, 2008: FHWA Issued 1st gusset plate analysis method draft March 2008: Gusset inspections began on the 25 specified bridges March – August 2008: Gusset plate load rating analyses refined based on inspection findings February 2009: FHWA published final draft of gusset plate analysis method titled - "Load Rating Guidance and Examples For Bolted and Riveted Gusset Plates in Truss Bridges" chiara.crosti@uniroma1.it FORENSIC INVESTIGATION
  51. 51. St. Cloud Bridge closed and replacement accelerated Blatnik Bridge in Duluth gusset stiffened to restore full safety factor Winona Bridge reinforced gusset due to corrosion Hastings Bridge unsupported edge stiffened to meet code requirements chiara.crosti@uniroma1.it FORENSIC INVESTIGATION
  52. 52. FORENSIC INVESTIGATION chiara.crosti@uniroma1.it Jennifer L. Zink, P.E. Bridge Inspection Mn/DOT Bridge Office
  53. 53. chiara.crosti@uniroma1.it Jennifer L. Zink, P.E. Bridge Inspection Mn/DOT Bridge Office FORENSIC INVESTIGATION
  54. 54. chiara.crosti@uniroma1.it FORENSIC INVESTIGATION Jennifer L. Zink, P.E. Bridge Inspection Mn/DOT Bridge Office
  55. 55. RESISTANCE OF GUSSET PLATES: GUSSET PLATES IN TENSION GUSSET PLATES SUBJECT TO SHEAR GUSSET PLATES IN COMPRESSION FHWA GUIDELINES, (February, 2009) 26/67 chiara.crosti@uniroma1.it FORENSIC INVESTIGATION RESISTANCE OF FASTENERS SHEAR RESISTANCE OF FASTENERS PLATE BEARING RESISTANCE AT FASTENERS http://bridges.transportation.org/Documents/FHWA-IF-09 014LoadRatingGuidanceandExamplesforGussetsFebruary2009rev3.pdf
  56. 56. CRITICAL REVIEW OF THE FHWA GUIDELINES: • Stiffness of framing members, that increase the ultimate compression capacity of the gusset plate; • Influence of the initial imperfections, that decrease the ultimate compression capacity of the gusset plate; • Edge buckling vs. Gusset plates buckling, from that the importance of making consideration not only on the length of the free edge, but also length of equivalent column is important for buckling 40/67 chiara.crosti@uniroma1.it Framing member stiffness Gusset Plates For LRFR and λ ≤ 2.25 (assumes δ ≤ L /1500) What if δ > L /1500) ? FORENSIC INVESTIGATION
  57. 57. chiara.crosti@uniroma1.it NIST PHYSICAL INFRASTRUCTURE PROGRAM NIST Physical Infrastructure Program
  58. 58. FHWA SETUP** chiara.crosti@uniroma1.it [**] Iadicola M., Ocel J., Zobel R., “Quantitative Evaluation of Digital Image Correlation for Large-Scale Gusset Plate Experiments”, IABMAS2012, Stresa, Lake Maggiore, Italy, July 8-12. NIST PHYSICAL INFRASTRUCTURE PROGRAM
  59. 59. chiara.crosti@uniroma1.it NIST PHYSICAL INFRASTRUCTURE PROGRAM FHWA TEST, VIRGINIA (2010)
  60. 60. Advanced computing modeling Hand calculation chiara.crosti@uniroma1.it 7/28 FHWA, 2009 chiara.crosti@uniroma1.it SIMPLIFIED CONNECTION MODEL
  61. 61. Connection element 1 Connection element 3 Connection element 4 n. connection elements: 5 Each connection element has a 6x6 stiffness matrix N. Nodes: 28330 n. Dof : 169980 n. Elements S4R and S3R: 27670 45/6 7 chiara.crosti@uniroma1.it MODELING OF GUSSET PLATE CONNECTIONS SUB-STRUCTURING ANALYSIS – SIMPLIFIED LINEAR CONNECTION MODEL
  62. 62. 59/67 chiara.crosti@uniroma1.it SUB-STRUCTURING ANALYSIS – SIMPLIFIED NONLINEAR CONNECTION MODEL MODELING OF GUSSET PLATE CONNECTIONS
  63. 63. ALL RIGID JOINT U10 W ALL RIGID JOINT + 1 SEMI-RIGID JOINT NorthSouth chiara.crosti@uniroma1.it 3D MODEL OF THE I35-W BRIDGE 3D FINITE ELEMENT MODEL Nodes: 1172 Beam elements: 1849
  64. 64. 56/67 NorthSouth 0 1 2 3 4 5 6 7 -0,7 -0,6 -0,5 -0,4 -0,3 -0,2 -0,1 0,0 LoadFactor Dz (m) RIGID JOINTS SEMI-RIGID JOINT Node at midspan 18/28 chiara.crosti@uniroma1.it NONLINEAR ANALYSES RESULTS NONLINEAR ANALYSES RESULTS
  65. 65. 0,0 0,2 0,4 0,6 0,8 1,0 1,2 1,4 1,6 1,8 -2,0E+07 -1,0E+07 0,0E+00 1,0E+07 2,0E+07 3,0E+07 LoadFactor Axial Forces (N) CONNECTION 1 CONNECTION 2 CONNECTION 3 CONNECTION 4 CONNECTION 5 AXIAL CAPACITY CONNECTION 1 AXIAL CAPACITY CONNECTION 2 AXIAL CAPACITY CONNECTION 3 AXIAL CAPACITY CONNECTION 4 AXIAL CAPACITY CONNECTION 5 57/6319/28 Compression Tension What is important to underline is not only the possibility to catch the collapse due to the failure of the connection, but moreover to classify the cause of the collapse which, in this case, happened because of the achievement for one of the connection elements of the maximum capacity in compression. chiara.crosti@uniroma1.it NONLINEAR ANALYSES RESULTS NONLINEAR ANALYSES RESULTS
  66. 66. Deformed shape (scale displacement of 10) at the ultimate load (Pu) of 1.2+07 N 62/67 chiara.crosti@uniroma1.it What is important to underline is not only the possibility to catch the collapse due to the failure of the connection, but moreover to classify the cause of the collapse which, in this case, happened because of the achievement for one of the connection elements of the maximum capacity in compression. CONCLUSIVE CONSIDERATIONS CONCLUSION Connection member Load ratio Tension or compression 1 0.28 Compression 2 0.56 Tension 3 1.00 Compression 4 0.02 Tension 5 0.41 Tension
  67. 67. I-35W Bridge was subjected constantly to inspection to assess its safety but even with that people in charge did not notice that the bridge was about to fail. A future work could be to develop parametric study on some particular shapes of gusset plates in order to identify some “critical” points where the monitoring of the out-plane displacements, could give to the owners of the bridges a warning of what it is happening in the connection. An idea of monitoring could have been done with a technique of monitoring developed by NIST who focuses its research on two areas of structural health monitoring: •development of non-destructive techniques; and •analysis for determining the degraded condition of infrastructural components and their subcomponents. FURTHER DEVELOPMENTS •FEA results•Results from monitoring ** chiara.crosti@uniroma1.itchiara.crosti@uniroma1.it CONCLUSION [**] Iadicola M., Ocel J., Zobel R., “Quantitative Evaluation of Digital Image Correlation for Large-Scale Gusset Plate Experiments”, IABMAS2012, Stresa, Lake Maggiore, Italy, July 8-12. •FHWA test
  68. 68. [**] Iadicola M., Ocel J., Zobel R., “Quantitative Evaluation of Digital Image Correlation for Large-Scale Gusset Plate Experiments”, IABMAS2012, Stresa, Lake Maggiore, Italy, July 8-12. chiara.crosti@uniroma1.it CONCLUSION
  69. 69. chiara.crosti@uniroma1.it I-35W SAINT ANTHONY FALLS BRIDGE (September 2008) CONCLUSION
  70. 70. •100-year life span •Design-build project complete in 339 days. •Designed to be aesthetically pleasing and fit in with its environment •The bridge was constructed with high-strength concrete •189 feet wide—the previous bridge was 113 feet wide •10 lanes of traffic, five in each direction—two lanes wider than the former bridge •13 foot wide right shoulders and 14 foot wide left shoulders, the previous bridge had no shoulders •Light Rail Transport-ready which may help accommodate future transportation needs •There are 323 sensors that regularly measure bridge conditions such as deck movement, stress, and temperature I-35W SAINT ANTHONY FALLS BRIDGE (September 2008) chiara.crosti@uniroma1.it CONCLUSION
  71. 71. chiara.crosti@uniroma1.it I-35W SAINT ANTHONY FALLS BRIDGE (September 2008) CONCLUSION
  72. 72. Opening day was six years ago, and the I-35W bridge is needing repairs — some that come from our harsh winters, but some from improper installations. chiara.crosti@uniroma1.it CONCLUSION
  73. 73. http://www.startribune.com/new-35w-bridge-already-is- aging/268746561/ chiara.crosti@uniroma1.it CONCLUSION
  74. 74. ACKNOWLEDGMENT The author would like to acknowledge: •Professor Franco Bontempi and his team, www.francobontempi.org, for the support and the help, •the Metallurgy division of the National Institute of Standard and Technology (NIST) in particular Dr. Dat Duthinh for the support and the help, •Eng. Piergiorgio Perin for providing the use of the finite element code Straus, and •NTSB and FHWA for allowing the access to the detailed FE model used in the investigation of the collapse of the I-35 W Bridge. chiara.crosti@uniroma1.it CONCLUSION

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"La lezione di Minneapolis", Ispezione dei ponti IABMAS ITALIA 2015

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