|
|
| [Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] |
************************************************************
NTSB ADVISORY
************************************************************
National Transportation Safety Board
Washington, DC 20594
March 17, 2008
************************************************************
FIFTH UPDATE: INVESTIGATION INTO COLLAPSE OF I-35 BRIDGE
************************************************************
The following is an update of the National
Transportation Safety Board's investigation into the August
1, 2007 collapse of the I-35W bridge in Minneapolis,
Minnesota.
NTSB Chairman Mark V. Rosenker today announced that
"significant progress continues to be made in the
investigation," and as a result he believes a final NTSB
report on the cause of the bridge's collapse and additional
safety recommendations should be able to be completed and
presented before the end of the year. "I applaud the team
for its expeditious, thorough and tireless investigation
thus far."
"We have gotten and continue to receive excellent
cooperation from the Federal Highway Administration and the
Minnesota Department of Transportation and have collected a
large body of evidence to this point."
As one result of that progress, Rosenker announced
that the Board's public docket on this investigation, which
comprises investigative reports of the NTSB group chairmen,
photos and information submitted by parties, has been made
available to the public on the Board's website beginning
today.
Details of the investigation's progress follow:
Load Capacity Calculations for Steel Truss Bridges
On January 15, 2008, the NTSB issued a recommendation
to the Federal Highway Administration (FHWA) calling on that
agency to require bridge owners (primarily States) to
conduct load capacity calculations to verify the stress
levels in all bridge structural elements (for non-load-path
redundant steel truss bridges), including gusset plates,
remain within applicable requirements whenever planned
modifications or operational changes may significantly
increase stresses. This was the result of the Board's
investigation finding that some of the gusset plates on the
I-35W bridge were under-sized because of an error in the
original design process.
Immediately following issuance of this recommendation,
the FHWA released a technical advisory to State Departments
of Transportation that supplements the American Association
of State Highway and Transportation Officials' (AASHTO)
procedures for load rating steel truss bridges. The FHWA is
continuing to develop guidance for load rating evaluations
of gusset plates in truss bridges, and will work with the
State DOTs to refine and finalize this guidance. Also
following the Safety Board's recommendation and FHWA's
technical advisory, States have initiated courses of action
to address the concerns raised. These actions generally
include identifying bridges that have undergone changes
during their lifetime, then analyzing and recalculating the
load carrying capacity of the gusset plates utilizing the
evolving FHWA guidance.
The Federal Highway Administration has provided the
NTSB with full access to the National Bridge Inventory
database and worked with Safety Board investigators to
define the population of highway bridges affected by the
NTSB recommendation.
Design Issues
The Bridge Design Group continues to investigate
design issues, including the review and approval process.
Sverdrup & Parcel was the original design consultant for the
I-35 bridge and had been acquired by The Jacobs Engineering
Group in 1999. Jacobs has provided archival information to
help investigators better understand what type of system of
checks and balances would have been in place when the bridge
was designed back in the 1960s.
Personnel from the Minnesota Department of
Transportation (MnDOT) have been interviewed regarding the
Department's role in quality control for the design review
process. These interviews have focused on what types and
level of review would have been conducted in the 1960s as
well as how the process works today. Interviews were also
conducted of FHWA personnel in the St. Paul District Office
regarding that agency's role in quality control. These
interviews have allowed investigators to better understand
how the oversight and design review process of the FHWA has
evolved from the 1960s to the system currently in place.
Additional private design consultants and State departments
of transportation are being identified as candidates for
further NTSB interviews regarding issues of quality control
and the design review process.
Computer Analysis
The Structures Modeling Group is continuing a complex
set of finite element computer analyses of the bridge, with
technical support from party members. This effort has also
involved contracted engineering support from the State
University of New York in Stony Brook and from Simulia, a
Rhode Island subsidiary of Dassault Systemes that develops
the Abaqus product suite for Finite Element Analysis.
Computer modeling of the bridge in its pre-collapse state is
well underway to help explore the potential causes for its
collapse.
In addition, the Board's Office of Research and
Engineering contracted with the University of Minnesota's
Department of Civil Engineering to construct a 1/200th scale
model of the I-35W bridge to provide investigators with a 3-
dimensional representation of the bridge's supporting
structure.
Digital Images
The Video and Photogrammetry Group is working to
identify and catalog approximately 20,000 digital images
taken by all parties throughout the on-scene investigation,
some of which are in the docket. Additionally, the group is
completing a study of the data captured by the surveillance
video camera located at the south lock on the west side of
the bridge, which recorded a portion of the bridge during
its collapse sequence. This report is currently undergoing
an internal technical review.
Wreckage Examination
In support of the Structural Investigation Group, the
NTSB Materials Laboratory is examining specific aspects of
the bridge, including nodes U10 East and West and the
corrosion areas on the gusset plates from nodes L11 East and
West. The Materials Lab is in the process of completing
several reports related to these examinations. These
sections of the bridge's superstructure have been removed
from the storage site in Minneapolis and transported to the
NTSB facilities for preservation, testing and further
evaluation.
Public Docket and Future Schedule
The NTSB maintains public dockets for its
investigations. These contain factual information gathered
by the various Safety Board investigative groups that will
be used by the Board in analyzing the accident and
formulating its final report and safety recommendations.
The following technical investigative group factual
reports are undergoing peer and managerial reviews, or have
been completed:
* Structural Investigation Group
* Witness Group
* Highway Construction Factors Group
* Survival Factors Group
* Bridge Design Factors Group
These factual reports are being placed in the public
docket as soon as they are completed. The docket currently
contains nearly 300 pages and includes the Structural
Investigation Group Report noted above. As of today, the
docket is available on the Board's website
http://www.ntsb.gov/dockets/Highway/HWY07MH024/default.htm
Additional reports will be placed on the website as they are
entered into the docket in the coming months.
Several additional investigative activities remain to
be conducted. These include the Structures Modeling Group's
efforts, which will continue for several more months as new
computer models are developed to examine specific failure
scenarios to help identify the cause of the collapse. Also,
the Structural Investigation Group is beginning a sequencing
study that will incorporate the physical evidence of the
wreckage, the surveillance video, and the findings of the
Structures Modeling Group, to determine, to the greatest
extent possible, the sequence of events that describe the
initial moments of the collapse. No determination has been
made as to the specific cause of the bridge's failure.
Because of the amount of factual information collected
during the investigation and the significant progress being
made, the Board has agreed with the investigative team not
to hold an interim investigative hearing. The team believes
that, barring unexpected developments, it is likely that a
final report will be ready for the Board to consider at a
public meeting in Washington, D.C. by the end of the year.
The final report will include the probable cause of the
collapse and will likely include additional safety
recommendations. That meeting will be open to the public
and press and available free of charge via webcast.
- 30 -
NTSB Media Contact: Terry Williams
(202) 314-6100
williat@xxxxxxxx
************************************************************
This message is delivered to you as a free service from the
National Transportation Safety Board.
You may unsubscribe at any time at
http://www.ntsb.gov/registration/registration.htm
An archive of press releases is available at
http://www.ntsb.gov/pressrel/pressrel.htm
Current job opportunities with the NTSB are listed at
http://www.ntsb.gov/vacancies/listing.htm
For questions/problems, contact pubinq@xxxxxxxx
[Home] [STB] [USDA] [Photography] [Yosemite News] [Hot Springs] [Steve's Art] [SB Lupus] [Railroad] [FDA News] [Flying Books]