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CROSTI_IABMAS-ITALY
1. MILANO, ITALY, OCTOBER 14, 2013
IL COLLASSO DEL PONTE I-35W A
MINNEAPOLIS COME ESEMPIO DI
INGEGNERIA FORENSE
Chiara Crosti
“Sapienza” University of Rome,
chiara.crosti@uniroma1.it
2. CASE STUDY
THE FACT:
COLLAPSE OF THE BRIDGE ON I 35-W MINNESOTA, AUGUST 1ST 2007
The I-35W Mississippi River Bridge (officially known as Bridge 9340) was an eight-lane, deck
truss bridge, designed by the engineering consulting firm of Sverdrup & Parcel and Associates,
the design plans were approved by the Minnesota Department of Transportation (Mn DOT) on
1965 and opened to traffic on 1967.
http://www.dot.state.mn.us/i35wbridge/ntsb/finalreport.pdf
chiara.crosti@uniroma1.it
3. CASE STUDY
•
•
•
The deck truss comprised in two parallel Warren
trusses (east and west) with verticals.
The east and west main trusses were spaced 22 m
apart and were connected by 27 transverse welded
floor trusses spaced 11.6 m on centers and by two
floor beams at the north and south ends.
Steel gusset plates were used on all the 112
connections of the two main trusses. All nodes had
two gusset plates on either side of the connection.
http://www.dot.state.mn.us/i35wbridge/ntsb/finalreport.pdf
chiara.crosti@uniroma1.it
4. CASE STUDY
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. “
chiara.crosti@uniroma1.it
5. 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 2008916213, Washington D.C. 20594.
chiara.crosti@uniroma1.it
6. FORENSIC INVESTIGATION
5/67
THE MAIN CAUSE:
The primary cause was the under-sized gusset plates, at 0.5 inches (13 mm) thick;
U10-W
[*] 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
7. FORENSIC INVESTIGATION
FINITE ELEMENT MODEL FOR OUTSIDE WEST GUSSET PLATE AT U10W
Stress contours for outside (west) gusset plate at U10W at time of bridge opening in 1967
Yield stress
of 51.5 ksi
1977-1998
South
North
[*] 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
8. FORENSIC INVESTIGATION
6/67
THE ADDITIONARY CAUSE:
2 inches (51 mm) of concrete were added to the road surface over the years,
increasing the dead load by 20%;
1977, Renovation:
Increased Deck Thickness
1998, Renovation:
Median Barrier, Traffic Railings,
and Anti-Icing System
2007, Repair and Renovation:
Repaving
[*] 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
9. FORENSIC INVESTIGATION
FINITE ELEMENT MODEL FOR OUTSIDE WEST GUSSET PLATE AT U10W
Stress contours for outside (west) gusset plate at U10W after 1977 and 1998 renovation projects
Yield stress
of 51.5 ksi
South
North
[*] 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
10. FORENSIC INVESTIGATION
7/67
THE ADDITIONARY CAUSE:
The extraordinary weight of construction equipment and material resting on the
bridge just above its weakest point at the time of the collapse
[*]
North
South
U10-W
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
[*] 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
11. FORENSIC INVESTIGATION
7/67
THE ADDITIONARY CAUSE:
The extraordinary weight of construction equipment and material resting on the
bridge just above its weakest point at the time of the collapse
[*]
North
South
U10-W
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
Pier 6
[*] 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
12. FORENSIC INVESTIGATION
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
South
North
[*] 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
13. FORENSIC INVESTIGATION
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
[*] 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
33. FORENSIC INVESTIGATION
26/67
FHWA GUIDELINES, (2009)
RESISTANCE OF GUSSET PLATES:
GUSSET PLATES SUBJECT TO SHEAR
GUSSET PLATES IN COMPRESSION
GUSSET PLATES IN TENSION
RESISTANCE OF FASTENERS
SHEAR RESISTANCE OF FASTENERS
PLATE BEARING RESISTANCE AT FASTENERS
http://bridges.transportation.org/Documents/FHWA-IF-09
014LoadRatingGuidanceandExamplesforGussetsFebruary2009rev3.pdf
chiara.crosti@uniroma1.it
34. FORENSIC INVESTIGATION
40/67
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
For LRFR and λ ≤ 2.25
(assumes δ ≤ L /1500)
Gusset Plates
What if δ > L /1500) ?
Framing member stiffness
chiara.crosti@uniroma1.it
36. NIST PHYSICAL INFRASTRUCTURE PROGRAM
FHWA SETUP**
[**] 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
39. MODELING OF GUSSET PLATE CONNECTIONS
45/6
7
SUB-STRUCTURING ANALYSIS – SIMPLIFIED LINEAR CONNECTION MODEL
N. Nodes: 28330
n. Dof : 169980
n. Elements S4R and S3R: 27670
Connection element 1
Connection element 3
n. connection elements: 5
Each connection element has a
6x6 stiffness matrix
Connection element 4
chiara.crosti@uniroma1.it
40. 3D MODEL OF THE I35-W BRIDGE
3D FINITE ELEMENT MODEL
U10 W
South
North
Nodes: 1172
Beam elements: 1849
ALL RIGID JOINT
ALL RIGID JOINT + 1 SEMI-RIGID JOINT
chiara.crosti@uniroma1.it
42. NONLINEAR ANALYSES RESULTS
57/63
19/28
NONLINEAR ANALYSES RESULTS
Compression
Tension
1.8
1.6
1.4
1.2
1.0
0.8
0.4
0.2
-2.0E+07
-1.0E+07
0.0E+00
1.0E+07
Axial Forces (N)
2.0E+07
Load Factor
0.6
0.0
3.0E+07
What is important to underline is not onlyCONNECTION 2
the possibility to catch the collapse due to the failure of
CONNECTION 1
CONNECTION 3
CONNECTION 4
CONNECTION 5
AXIAL CAPACITY CONNECTION 1
the connection, but moreover to classify the cause of the collapse which, in this case, happened
AXIAL CAPACITY CONNECTION 2
AXIAL CAPACITY CONNECTION 3
AXIAL CAPACITY CONNECTION 4
because of the achievement for one of the connection elements of the maximum capacity in
AXIAL CAPACITY CONNECTION 5
compression.
chiara.crosti@uniroma1.it
43. CONCLUSION
62/67
CONCLUSIVE CONSIDERATIONS
Deformed shape (scale displacement of 10)
at the ultimate load (Pu) of 1.2+07 N
Connection
Load
Tension or
member
ratio
compression
1
0.28
Compression
2
0.56
Tension
3
1.00
Compression
4
0.02
Tension
5
0.41
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
44. CONCLUSION
FURTHER DEVELOPMENTS
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.
•Results from monitoring **
•FEA results
•FHWA test
[**] 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
chiara.crosti@uniroma1.it
45. 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.
chiara.crosti@uniroma1.it
46. CONCLUSION
I-35W SAINT ANTHONY FALLS BRIDGE (September 2008)
There are 323 sensors that regularly measure bridge conditions
such as deck movement, stress, and temperature
chiara.crosti@uniroma1.it
47. CONCLUSION
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
