Civil Engineering
Civil Engineering
Posted on Jun 5, 2021
Is seismic retrofit to blame for ‘unusual’ failure in Mississippi River bridge? | New Civil...
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https://www.newcivilengineer.com/latest/is-seismic-retrofit-to-blame-for-unusual-failure-in-mississippi-river-bridge-14-05-2021/?utm_medium=email&utm_source=rasa_io&PostID=30311312&MessageRunDetailID= [login to see]
Another RP member brought up this failure about a month ago and I commented on it being unusual; it does look like a truss bridge tension member failed in shear, that usually indicates a fatigue failure… but that just doesn’t happen in this type of a portion of a bridge member. Now they say the bridge had a seismic retrofit that typically helps portions of bridges resist vertical and/or lateral thrusts from earthquakes. Maybe if a brace was added that caused a force in a direction other than that was intended in the original design, it might have caused the failure.
A major road bridge over the Mississippi River has been closed after a complete break was discovered in one of its steel support beams.
The fault was found during a routine inspection of the Interstate 40 steel tied arch bridge – also known as the Hernando DeSoto Bridge – that connects Arkansas with Memphis in the USA.
Arkansas Department of Transportation director Lorie Tudor said that the fault had "the potential of becoming a catastrophic event" had it not been caught.
The cause of the damage is under investigation, but Tudor said stress caused by wear and tear on the 50-year-old bridge was likely a factor.
After examining images of the damage, independent bridge consultant Simon Bourne told NCE that the location of the break appeared unusual.
“Unusually, the failure is not at the joint or within the bolted splice area, suggesting that it is not a fatigue issue, even though the bridge is around 50 years old,” Bourne said.
“There is also no sign of any corrosion or other deterioration, although the failed surface looks quite old, suggesting that it might have been like this for a while.”
He added that the fractured longitudinal member is “absolutely fundamental to the strength of the whole bridge”.
Bourne suspects that the crack has developed over a number of decades due to the vertical movements in the deck.
He added that a project to retrofit the bridge in recent years could have “exacerbated” the issue.
He added: “It’s very serious, there are no signs of corrosion, but most likely it’s a fatigue crack that has developed over 50 years due to the vertical movements of the deck, causing a complete shear failure of this main tie/tension member.
"It's a wonder that the whole bridge hasn't fallen down."
Bourne added that bracing elements added during a retrofit of the bridge could have exaggerated the damage which was likely caused by vertical movements of the older deck and vertical girders.
“The more recent seismic retro-fitting may well have exacerbated the issue," Bourne said. "The location of additional bracing is very close to the site of the crack so it is highly likely that is would have had some impact and one would assume that it has been detrimental."
The retrofit was carried out to both the I-40 and 1-55 Mississippi River bridges from 2000 to 2015 to provide a "post-earthquake" lifeline link for emergency vehicles and the general public. TRC (formerly Imbsen & Associates) provided engineering services for all phases of the $268.4M (£191M) project, including seismic analysis, retrofit design and retrofit construction.
A project report by TRC reveals that extensive strengthening or complete replacement was carried out to numerous components of the bridge.
The retrofit strategy consisted of the following work:
Bent cap retrofit / widening
Column strengthening
Webwall retrofit
Footing retrofit / enlarged cap with additional piles superstructure
Diaphragm / cross frame replacement
Bottom lateral retrofit
Bearing replacement – 112 bearings
Expansion joint R=replacement
The 5.3km I-40 bridge was first opened to traffic in 1973 and is comprised of 164 spans, 160 piers, and 10 abutments.
Arkansas and Tennessee share responsibility for maintaining the bridge. Arkansas DOT deputy director Rex Vines said that the fault was not noted on the bridge's last inspection, which was carried out in September 2020.
The bridge has now been closed indefinitely. TRC has been approached for comment.
Another RP member brought up this failure about a month ago and I commented on it being unusual; it does look like a truss bridge tension member failed in shear, that usually indicates a fatigue failure… but that just doesn’t happen in this type of a portion of a bridge member. Now they say the bridge had a seismic retrofit that typically helps portions of bridges resist vertical and/or lateral thrusts from earthquakes. Maybe if a brace was added that caused a force in a direction other than that was intended in the original design, it might have caused the failure.
A major road bridge over the Mississippi River has been closed after a complete break was discovered in one of its steel support beams.
The fault was found during a routine inspection of the Interstate 40 steel tied arch bridge – also known as the Hernando DeSoto Bridge – that connects Arkansas with Memphis in the USA.
Arkansas Department of Transportation director Lorie Tudor said that the fault had "the potential of becoming a catastrophic event" had it not been caught.
The cause of the damage is under investigation, but Tudor said stress caused by wear and tear on the 50-year-old bridge was likely a factor.
After examining images of the damage, independent bridge consultant Simon Bourne told NCE that the location of the break appeared unusual.
“Unusually, the failure is not at the joint or within the bolted splice area, suggesting that it is not a fatigue issue, even though the bridge is around 50 years old,” Bourne said.
“There is also no sign of any corrosion or other deterioration, although the failed surface looks quite old, suggesting that it might have been like this for a while.”
He added that the fractured longitudinal member is “absolutely fundamental to the strength of the whole bridge”.
Bourne suspects that the crack has developed over a number of decades due to the vertical movements in the deck.
He added that a project to retrofit the bridge in recent years could have “exacerbated” the issue.
He added: “It’s very serious, there are no signs of corrosion, but most likely it’s a fatigue crack that has developed over 50 years due to the vertical movements of the deck, causing a complete shear failure of this main tie/tension member.
"It's a wonder that the whole bridge hasn't fallen down."
Bourne added that bracing elements added during a retrofit of the bridge could have exaggerated the damage which was likely caused by vertical movements of the older deck and vertical girders.
“The more recent seismic retro-fitting may well have exacerbated the issue," Bourne said. "The location of additional bracing is very close to the site of the crack so it is highly likely that is would have had some impact and one would assume that it has been detrimental."
The retrofit was carried out to both the I-40 and 1-55 Mississippi River bridges from 2000 to 2015 to provide a "post-earthquake" lifeline link for emergency vehicles and the general public. TRC (formerly Imbsen & Associates) provided engineering services for all phases of the $268.4M (£191M) project, including seismic analysis, retrofit design and retrofit construction.
A project report by TRC reveals that extensive strengthening or complete replacement was carried out to numerous components of the bridge.
The retrofit strategy consisted of the following work:
Bent cap retrofit / widening
Column strengthening
Webwall retrofit
Footing retrofit / enlarged cap with additional piles superstructure
Diaphragm / cross frame replacement
Bottom lateral retrofit
Bearing replacement – 112 bearings
Expansion joint R=replacement
The 5.3km I-40 bridge was first opened to traffic in 1973 and is comprised of 164 spans, 160 piers, and 10 abutments.
Arkansas and Tennessee share responsibility for maintaining the bridge. Arkansas DOT deputy director Rex Vines said that the fault was not noted on the bridge's last inspection, which was carried out in September 2020.
The bridge has now been closed indefinitely. TRC has been approached for comment.
Is seismic retrofit to blame for ‘unusual’ failure in Mississippi River bridge? | New Civil...
Posted from newcivilengineer.com
Transportation
12C: Bridge Crewmember
Civil Engineering
Edited 3 y ago
Posted 3 y ago
Responses: 3
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New Madrid Fault created at least one lake in NW TN, and a reversal of MS River in 1812. We still have rumblings fairly often. https://www.usgs.gov/natural-hazards/earthquake-hazards/science/new-madrid-seismic-zone?qt-science_center_objects=0#qt-science_center_objects
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CWO3 (Join to see)
I don't know mechanics enough to say, but from a maintenance viewpoint any shear failure usually indicates outside forces i.e. seismic, exceeding capability, or a flaw in design.
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SFC (Join to see)
While it appears to be a shear failure looking at the entire member the way we are, it is still possible it is a tension failure. This is an old bridge and the earlier steel/iron used in those times could break looking like a shear in tension sometimes to the naked eye. I would have to look at a magnified section of it to determine that. We just don't have enough information. That this failure was discovered shortly after a retrofit may be telling, it may also not be telling. I have designed rehabilitations of camelback truss bridges in the past, they are not easy and there were many items to consider that weren't self evident, so I will wait to see what else is reported on this investigation.
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SFC (Join to see)
Harmonics played a big part in the camelbacks I worked on. As for the other stuff they are all valuable tools in identifying problems.
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I can’t speak to the structural engineering aspects of the failed bridge SFC (Join to see), but I can tell you that the traffic will be horrible! I lived in Memphis for two years and crossed the Hernando de Soto bridge countless times. However, there’s only one other bridge that crosses the Mississippi River in Memphis! That one bridge will now sustain the entire traffic load! Ugh! The bridge that failed is the northernmost bridge on the map.
SGT (Join to see)
SGT (Join to see)
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SFC (Join to see)
God Bless all those people. Hopefully the site allows for a quick erection of a temporary bridge until they can repair or replace the main bridge. Thanks for the context the map provides.
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CWO3 (Join to see)
SFC (Join to see) - Running a bead will not fix this one. They'll have to factor seismics in, and who knows how soon that will happen.
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CWO3 (Join to see)
It may be a relatively simple fix too. The Fault is only one dot. The force of those heavy trucks hitting joints could add up. They run a MTBF on components during design as you have likely taught. Or they are supposed to.
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SFC (Join to see)
Arkansas and Tennessee share responsibility for maintaining the bridge. Arkansas DOT deputy director Rex Vines said that the fault was not noted on the bridge's last inspection, which was carried out in September 2020.
The bridge has now been closed indefinitely.
Arkansas and Tennessee share responsibility for maintaining the bridge. Arkansas DOT deputy director Rex Vines said that the fault was not noted on the bridge's last inspection, which was carried out in September 2020.
The bridge has now been closed indefinitely.
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SFC (Join to see)
Being a former certified bridge inspector and engineer for PennDOT Dist. 4-0 I can tell you all Dot's are looking very closely if they have any situations like this.
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