Jump to content

Florida International University pedestrian bridge collapse: Difference between revisions

Coordinates: 25°45′40″N 80°22′22″W / 25.7612°N 80.3728°W / 25.7612; -80.3728
From Wikipedia, the free encyclopedia
Browse history interactively
← Previous editNext edit →
Content deleted Content added
VisualWikitext
m →Collapse: Minor ce
→Bridge design: If any strut fails, the entire structure then folds and fails.{{cn}}
Line 156: Line 156:
The bridge used concrete diagonal struts arranged to align with cables from an off-center pylon, rather than a conventional truss pattern forming symmetric triangles.<ref name=":5">{{Cite news|url=https://www.usatoday.com/story/news/2018/03/16/miami-bridge-collapse-suspension-cables-support-tower/431418002/|title=Miami bridge that collapsed was a truss design, despite the cosmetic tower, support cables|last=Jansen|first=Bart|date=March 16, 2018|work=USA Today|access-date=March 17, 2018|archive-url=|archive-date=|dead-url=|language=en}}</ref><ref name=":6">{{cite AV media |publisher=[[WSVN-TV]] |via=[[YouTube]] |others=Robert Accetta (press briefing speaker) |date=March 16, 2018 |title=FIU Bridge Collapse NTSB Update |url=https://www.youtube.com/watch?v=u3Gj1Nu_kjo |access-date=March 19, 2018 |at=5:25-6:00}}</ref> This visually gave the impression that this was a cable-stay bridge supported from above. The superstructure of the bridge was unusually heavy due to a concrete upper roof deck, concrete trusses, concrete base, and its length.<ref name=":7">{{cite news|url=http://www.miamiherald.com/news/local/community/miami-dade/article205422719.html|title=Stress test may have contributed to collapse of FIU pedestrian bridge|last=Staletovich|first=Jenny|accessdate=March 18, 2018|last2=Rodriguez|first2=Rene|last3=Flechas|first3=Joey}}</ref> The superstructure design employs a "re-invented" [[I-beam]] concept. The bottom concrete flange becomes the pedestrian walkway, the top concrete flange becomes the canopy, and the web becomes a series of struts connecting to a single pylon with stays.<ref name=":4">{{cite news|url=http://facilities.fiu.edu/projects/BT_904/MCM_FIGG_Proposal_for_FIU_Pedestrian_Bridge_9-30-2015.pdf|title=MCM design-build proposal|author=MCM|accessdate=March 18, 2018}}</ref> The struts contain post-tensioning rods that connect the flanges, and are adjusted as needed.<ref>{{Cite news|url=https://www.chicagotribune.com/news/sns-bc-us--university-bridge-collapse-20180317-story.html|title=Bridge collapse victim's uncle rages at 'incompetence'|author=Jennifer Kay and Allen G. Breed|date=March 18, 2018|work=Chicago Tribune|access-date=March 18, 2018|archive-url=|archive-date=|dead-url=|language=en}}</ref>
The bridge used concrete diagonal struts arranged to align with cables from an off-center pylon, rather than a conventional truss pattern forming symmetric triangles.<ref name=":5">{{Cite news|url=https://www.usatoday.com/story/news/2018/03/16/miami-bridge-collapse-suspension-cables-support-tower/431418002/|title=Miami bridge that collapsed was a truss design, despite the cosmetic tower, support cables|last=Jansen|first=Bart|date=March 16, 2018|work=USA Today|access-date=March 17, 2018|archive-url=|archive-date=|dead-url=|language=en}}</ref><ref name=":6">{{cite AV media |publisher=[[WSVN-TV]] |via=[[YouTube]] |others=Robert Accetta (press briefing speaker) |date=March 16, 2018 |title=FIU Bridge Collapse NTSB Update |url=https://www.youtube.com/watch?v=u3Gj1Nu_kjo |access-date=March 19, 2018 |at=5:25-6:00}}</ref> This visually gave the impression that this was a cable-stay bridge supported from above. The superstructure of the bridge was unusually heavy due to a concrete upper roof deck, concrete trusses, concrete base, and its length.<ref name=":7">{{cite news|url=http://www.miamiherald.com/news/local/community/miami-dade/article205422719.html|title=Stress test may have contributed to collapse of FIU pedestrian bridge|last=Staletovich|first=Jenny|accessdate=March 18, 2018|last2=Rodriguez|first2=Rene|last3=Flechas|first3=Joey}}</ref> The superstructure design employs a "re-invented" [[I-beam]] concept. The bottom concrete flange becomes the pedestrian walkway, the top concrete flange becomes the canopy, and the web becomes a series of struts connecting to a single pylon with stays.<ref name=":4">{{cite news|url=http://facilities.fiu.edu/projects/BT_904/MCM_FIGG_Proposal_for_FIU_Pedestrian_Bridge_9-30-2015.pdf|title=MCM design-build proposal|author=MCM|accessdate=March 18, 2018}}</ref> The struts contain post-tensioning rods that connect the flanges, and are adjusted as needed.<ref>{{Cite news|url=https://www.chicagotribune.com/news/sns-bc-us--university-bridge-collapse-20180317-story.html|title=Bridge collapse victim's uncle rages at 'incompetence'|author=Jennifer Kay and Allen G. Breed|date=March 18, 2018|work=Chicago Tribune|access-date=March 18, 2018|archive-url=|archive-date=|dead-url=|language=en}}</ref>


The diagonal struts are here arranged along the walkway's centerline. There is no backup for any strut. If any strut fails, the entire structure then folds and fails. The bridge is [[National Bridge Inventory|fracture critical]] with each strut being a potential [[single point of failure]]. That is avoided in most new bridges.
The diagonal struts are here arranged along the walkway's centerline. There is no backup for any strut. If any strut fails, the entire structure then folds and fails.{{cn}} The bridge is [[National Bridge Inventory|fracture critical]] with each strut being a potential [[single point of failure]]. That is avoided in most new bridges.


== Collapse ==
== Collapse ==

Revision as of 09:30, 19 March 2018

Florida International University pedestrian overpass collapse
National Transportation Safety Board members inspecting the collapsed pedestrian overpass on March 16
DateMarch 15, 2018 (2018-03-15)
Time1:30 p.m. EDT
LocationUniversity Park and Sweetwater, Florida, U.S.
TypeOverpass section collapse
Deaths6
Non-fatal injuries9
Map
About OpenStreetMaps
Maps: terms of use
750m
780yds
Collapse site
Collapse site

On March 15, 2018, a 174-foot-long (53 m), recently-erected section of the FIU–Sweetwater UniversityCity Bridge collapsed onto the Tamiami Trail (U.S. Route 41).

The pedestrian bridge was located in front of the campus of Florida International University (FIU) in University Park, a suburb west of Miami, Florida, United States, and was in the process of post-tension cable adjustment when it suddenly failed.[1] The road beneath it had been opened to traffic. Several occupied vehicles were crushed underneath, and six deaths and nine injuries have been reported.[2]

Background

The FIU–Sweetwater UniversityCity Bridge, located just west of the intersection of Tamiami Trail (Southwest 8th Street) and Southwest 109th Avenue[3], was planned to connect the FIU campus to student housing neighborhoods in Sweetwater.[4] It was intended to improve pedestrian safety, as the busy crosswalks at this wide, busy intersection had been identified as a safety hazard and the site of fatal collisions.[5] The $14.2 million project was funded with a $19.4 million Transportation Investment Generating Economic Recovery (TIGER) grant from the United States Department of Transportation in 2013, along with state agencies.[6] The bridge itself cost $9 million to construct.[7]

The main companies behind the construction project are Munilla Construction Management, or MCM, the Miami-based construction management firm and FIGG Bridge Engineers, a Tallahassee firm.[8] Unlike most bridges in Florida, the design for this project was overseen by the university itself, not the Florida Department of Transportation.

The full 320-foot-long (98 m) pedestrian overpass was to cross both a major roadway and a parallel water canal. Tamiami Trail here has six lanes of traffic plus two turn lanes. One main span of the bridge, crossing the roadway only, was rolled into place and erected five days earlier on Saturday, March 10. The second canal span, access ramps, and cable-stay tower had not yet been built. Pedestrian use was to begin when the whole project was complete. The school was on spring break at the time of collapse.[1] The section of the bridge that collapsed weighed 950 short tons (860 metric tons) and fell onto several vehicles on the roadway below.

Construction of the bridge began in March 2016 and was scheduled to be completed in December 2018.[7][9] The bridge's prefabricated main span was assembled adjacent to the highway and constructed using accelerated bridge construction (ABC), a technique promoted at the university.[1] It was lifted into place on Saturday morning, March 10, five days before the collapse, during a weekend closure of the highway.[10][11] The ABC method was touted to "...significantly reduce the risk to workers, walkers, drivers and minimize traffic disruptions for construction."[1][clarification needed] The span was installed by Munilla Construction Management.[12][13]

Bridge design

FIU-Sweetwater UniversityCity Bridge
Coordinates25°45′40″N 80°22′22″W / 25.7612°N 80.3728°W / 25.7612; -80.3728
CarriedPedestrian traffic
CrossedTamiami Trail
LocaleUniversity Park and Sweetwater, Florida, U.S.
Characteristics
Total length320 feet (98 m)
Longest span175 feet (53 m)
History
Engineering design byFIGG Bridge Engineers
Constructed byMunilla Construction Management
Construction cost$14.2 million
CollapsedMarch 15, 2018
Location
Map

The new pedestrian bridge was designed to connect the campus to student housing in a dramatic sculptural way, and also to showcase the school's leadership in the ABC method of rapid bridge construction.[14]

Florida International University is known for its expertise in accelerated bridge construction, and has attracted international scholars as PhD students.[15] It is home to the federally-funded Accelerated Bridge Construction University Transportation Center, which sponsors industry conferences and seminars.[16]

The bridge was made of concrete rather than steel, to avoid bouncy vibrations from footsteps on this long span.[14] Concrete structures are generally 10 times heavier than equivalent steel designs.[17] The bridge was made using a new formulation for concrete that aims to not require cleaning. It stays white just from the action of sunlight.[18]

Concrete by itself is very weak when carrying tension (pulling-apart) forces. In a bridge, the weight of bridge and traffic cause many parts to be under tension, not compression. Concrete structures are made strong by embedding steel rods or cables that are stretched before being locked to the concrete. The tension in the steel keeps the concrete under compression and strong despite the overall loads. In the main bridge span, the concrete floor deck, roof, and diagonal struts each contained post-tensioner rods whose pull could be adjusted after the concrete was cured.[14] Adjustments were expected each time the span was moved onto a different foundation with different support points.

The bridge was meant to last more than 100 years, and to withstand a Category 5 hurricane, in a statement by the university.[19]

The full bridge project was styled to look like a cable-stayed bridge with tower and high cables for dramatic effect. But functionally and structurally it was actually a truss bridge, with the spans being fully self-supporting.[14][20][21] The planned tower would take up little of the spans' weight. The tower cables do have a minor structural function, of bracing the spans against footstep vibrations. As a truss bridge, it was feasible to quickly roll in the completed main span by itself, without the tower, without the counterweight of the canal span, and without temporary piers in the roadway. A true cable-stay bridge would be built in stages outward from the tower, hanging pairs of deck segments on each side of the tower as counterweights.

The bridge used concrete diagonal struts arranged to align with cables from an off-center pylon, rather than a conventional truss pattern forming symmetric triangles.[20][21] This visually gave the impression that this was a cable-stay bridge supported from above. The superstructure of the bridge was unusually heavy due to a concrete upper roof deck, concrete trusses, concrete base, and its length.[17] The superstructure design employs a "re-invented" I-beam concept. The bottom concrete flange becomes the pedestrian walkway, the top concrete flange becomes the canopy, and the web becomes a series of struts connecting to a single pylon with stays.[14] The struts contain post-tensioning rods that connect the flanges, and are adjusted as needed.[22]

The diagonal struts are here arranged along the walkway's centerline. There is no backup for any strut. If any strut fails, the entire structure then folds and fails.[citation needed] The bridge is fracture critical with each strut being a potential single point of failure. That is avoided in most new bridges.

Collapse

Schematic of the bridge at time of collapse. Red highlights the diagonal support that was being post-tensioned at the time of collapse. The black portions had not yet been constructed. Two westbound lanes (the leftmost in the image) were closed at the time of the collapse.

Cracking

On Tuesday, March 13, the third day after lifting of the main span, the project's lead engineer discovered cracks at the north end of the span (the end that later broke). He reported this by voicemail to a Florida Department of Transportation (FDOT) employee. He thought this was not an immediate safety issue, merely something that would need to be repaired later. The FDOT recipient was away for several days and did not hear this message until the day after the collapse.[23][24]

At 9 a.m. on Thursday, March 15, a university employee heard a loud "whip cracking" sound while under the bridge span, waiting for a red traffic light.[25] At the same time, the design-build team met for about two hours at the construction site to discuss the cracks discovered Tuesday. Representatives from both FIU and the FDOT were present. The FIGG lead engineer's conclusions were that the structural integrity of the bridge was not compromised and that there were no safety concerns raised by the presence of the crack.[26]

The mayor of Miami-Dade County, Carlos A. Giménez, said that workers conducted a stress test on Thursday morning.[27]

United States Senator and FIU adjunct professor Marco Rubio tweeted that engineers were tightening loosened cables on Thursday:[27] workers were adding more tension to the steel rod (tendon) inside a concrete diagonal strut at the north end.[28] The National Transportation Safety Board, who are investigating the collapse, stated that crews were applying "post-tensioning force" on the bridge before the collapse.[29]

Collapse

At approximately 1:30 p.m., the north end of the installed bridge span sagged deeply, then fractured at the first diagonals, folded, and immediately dropped the heavy full span onto the roadway below. A surveillance video shows the collapse sequence took only a few video frames.[30]

A witness reported that at the moment of collapse, a blue box fell loose from the hook of a crane. His impression was that its fall triggered the collapse.[31] It dropped onto the roof of the bridge next to workers, and where the roof and span broke apart. A video shows that it likely shook loose as a result of the upheaval, rather than being the trigger.[32] In the videos, this is the larger dark crane not the smaller green boom lift. The blue box was a hydraulic pump for the post-tension jack, and was most likely not dropped but flung into the air by a cable or strap during upper chord failure.[citation needed] The crane was used to maneuver the jack and pump.

Post-collapse photos of the roof at the northernmost diagonals show a post-tensioning rod jutting out 6 feet from the wreckage, with a blue-colored hydraulic jack still attached.[33]

The span that collapsed weighed 950 short tons (861 tonnes).[34]

At the time of the collapse, the roadway was open and there were multiple cars stopped at a traffic light under the span.[35][36][37] Eight cars are reported to have been crushed. Six deaths were reported, with nine injured; while early reports said that the death toll was expected to rise,[2] authorities said on March 18 that all bodies had been accounted for.[38] One construction worker was killed and two others were hospitalized; an FIU student was also presumed dead.[39]

Aftermath

On March 16, the Florida Highway Patrol announced Southwest 8th Street between Southwest 107th and 117th Avenues and the eastbound Southwest 8th Street exit from the Florida Turnpike would be closed indefinitely while debris removal and investigations were conducted.[40] A team of 15 people from the National Transportation Safety Board (NTSB) began their investigation that morning.[41]

See also

Wikinews has related news:

References

  1. ^ a b c d Viglucci, Andres; Madan, Monique O.; Hanks, Douglas; Chang, Daniel (March 15, 2018). "FIU pedestrian overpass section collapses days after placement; police say multiple deaths, occupied vehicles trapped". Miami Herald. Retrieved March 15, 2018.
  2. ^ a b Shapiro, Emily; Doom, Justin (March 16, 2018). "Bridge collapse death toll likely to rise as investigators sift through rubble". ABC News. Retrieved March 16, 2018.
  3. ^ "FIU Bridge Collapse: Four Dead, 8 Cars Trapped Underneath". CBS Miami. March 15, 2018. Retrieved March 17, 2018.
  4. ^ Ashaboglu, Selin (March 15, 2018). "Miami Pedestrian Bridge Collapses". ARCHITECT. Retrieved March 15, 2018.
  5. ^ Rodriguez, Marybel (August 22, 2017). "Pedestrian Bridge In The Works For FIU Students To Cross Busy 8th Street". CBS 4 Miami. Retrieved March 15, 2018.
  6. ^ "FIU Pedestrian Bridge Construction Using Innovative Approach By Swinging Into Place". CBSLocal. WFOR-TV. March 10, 2018. Retrieved March 15, 2018.
  7. ^ a b Harris, Alex (August 24, 2017). "A walking bridge for FIU students is coming soon. But it's too late for one student". Miami Herald. Retrieved March 15, 2018.
  8. ^ Gomez Licon, Adriana; Replogle, Josh (March 16, 2018). "Tearful families wait as bodies remain under failed bridge". Associated Press. Retrieved March 17, 2018.
  9. ^ Kiah, Clara-Meretan (March 30, 2016). "FIU, Sweetwater break ground for bridge to the future". Florida International University. Retrieved March 15, 2018.
  10. ^ Viglucci, Andres (March 10, 2018). "'Instant' bridge aims to make a dangerous crossing safer for thousands of students". Miami Herald. Retrieved March 15, 2018.
  11. ^ Madan, Monique O. (March 8, 2018). "If you plan to drive on SW Eighth Street this weekend, you'll be rerouted here". Miami Herald. Retrieved March 15, 2018.
  12. ^ Fagenson, Zachary (March 15, 2018). "Several killed, cars crushed in Florida foot bridge collapse". Reuters. Retrieved March 15, 2018.
  13. ^ Smiley, David; Nehamas, Nicholas; Hanks, Douglas; Blaskey, Sarah (March 16, 2018). "Meet MCM and FIGG, the two firms behind FIU's collapsed pedestrian bridge". Miami Herald. Retrieved March 16, 2018.
  14. ^ a b c d e MCM. "MCM design-build proposal" (PDF). Retrieved March 18, 2018.
  15. ^ Bridge Collapse Saps Spirits and Research Efforts at Florida International University, By PATRICIA MAZZEI and STEPHANIE SAUL, New York Times, MARCH 17, 2018
  16. ^ "Home - Accelerated Bridge Construction". Accelerated Bridge Construction. Retrieved March 19, 2018.
  17. ^ a b Staletovich, Jenny; Rodriguez, Rene; Flechas, Joey. "Stress test may have contributed to collapse of FIU pedestrian bridge". Retrieved March 18, 2018.
  18. ^ News, F. I. U. (March 10, 2018). "#DidYouKnow the new pedestrian bridge that will connect our FIU and the @CitySweetwater is the first in the world to be constructed entirely of self-cleaning concrete? #WorldsAheadpic.twitter.com/lQVJh09Pv2". @FIUnews. Retrieved March 17, 2018. {{cite web}}: |last= has generic name (help)
  19. ^ Video clip, WPBF News, Mar 16, 2018, Collapsed bridge meant to last 100 years
  20. ^ a b Jansen, Bart (March 16, 2018). "Miami bridge that collapsed was a truss design, despite the cosmetic tower, support cables". USA Today. Retrieved March 17, 2018. {{cite news}}: Cite has empty unknown parameter: |dead-url= (help)
  21. ^ a b FIU Bridge Collapse NTSB Update. Robert Accetta (press briefing speaker). WSVN-TV. March 16, 2018. Retrieved March 19, 2018 – via YouTube.{{cite AV media}}: CS1 maint: others in cite AV media (notes) (link)
  22. ^ Jennifer Kay and Allen G. Breed (March 18, 2018). "Bridge collapse victim's uncle rages at 'incompetence'". Chicago Tribune. Retrieved March 18, 2018. {{cite news}}: Cite has empty unknown parameter: |dead-url= (help)
  23. ^ CNN, Madison Park, Jason Hanna, Joe Sutton and Steve Almasy,. "Engineer advised of cracking on bridge two days before collapse". CNN. Retrieved March 17, 2018. {{cite news}}: |last= has generic name (help)CS1 maint: extra punctuation (link) CS1 maint: multiple names: authors list (link)
  24. ^ http://www.bostonherald.com/news/national/2018/03/state_voicemail_about_cracking_in_bridge_wasnt_picked_up?utm_source=Twitter&utm_medium=socialflow
  25. ^ "FIU employee heard a loud crack crossing under the bridge. Hours later, it collapsed". miamiherald. Retrieved March 17, 2018.
  26. ^ Mier, Alyse (March 17, 2017). "FIU statement" (Press release). FIU. Retrieved March 17, 2018.
  27. ^ a b "Rubio says engineers were tightening loose cables when the FIU bridge collapsed". miamiherald. Retrieved March 17, 2018.
  28. ^ CNN, Madison Park, Jason Hanna, Joe Sutton and Steve Almasy,. "Engineer advised of cracking on bridge two days before collapse". CNN. Retrieved March 17, 2018. {{cite news}}: |last= has generic name (help)CS1 maint: extra punctuation (link) CS1 maint: multiple names: authors list (link)
  29. ^ "Bridge victim's grieving uncle lashes out at 'incompetence'". AP News. Retrieved March 18, 2018.
  30. ^ "Miami bridge collapsed during 'stress testing' killing at least four". Mail Online. Retrieved March 17, 2018.
  31. ^ "Found Video: Miami Bridge Collapsed During Stress Test Conducted in Afternoon Traffic". Santa Monica Observer. Retrieved March 17, 2018.
  32. ^ "New video surfaces of FIU bridge collapse from view of driver who witnessed it". Miami Herald. March 17, 2018 01:18 PM. {{cite news}}: Check date values in: |date= (help)
  33. ^ "At least six dead after Florida college campus bridge collapses". NY Daily News. Retrieved March 19, 2018.
  34. ^ Cochrane, Karen (March 16, 2017). "Pedestrian Bridge FAQ" (Press release). FIU. Retrieved March 17, 2018.
  35. ^ Svrluga, Susan; Siddiqui, Faiz (March 15, 2018). "New pedestrian bridge collapses at Florida International University, crushing eight cars driving underneath". The Washington Post. Retrieved March 15, 2018.
  36. ^ Batchelor, Amanda; Suarez, Carlos (March 15, 2018). "Several dead after newly-installed portion of FIU pedestrian bridge collapses". Local 10 News. Retrieved March 15, 2018.
  37. ^ "Florida Pedestrian Bridge Collapses During Stress Test Conducted in Afternoon Traffic". Santa Monica Observer. Retrieved March 16, 2018.
  38. ^ "Florida Bridge Collapse Moves Into Investigation Phase". The Wall Street Journal. March 18, 2018. Retrieved March 19, 2018.
  39. ^ Mazzei, Patricia; Robles, Frances; Dickerson, Caitlin (March 16, 2018). "They Were Heading Home, to Lunch, to Work. Then a Bridge Came Crashing Down". The New York Times. Retrieved March 18, 2018.
  40. ^ "Southwest 8th Street To Be Closed As Bridge Collapse Is Investigated". CBS Miami. March 16, 2018. Retrieved March 16, 2018.
  41. ^ Bowden, John (March 15, 2018). "NTSB chairman: Agency will investigate Florida bridge collapse". The Hill. Retrieved March 16, 2018.
Retrieved from "https://en.wikipedia.org/enwiki/w/index.php?title=Florida_International_University_pedestrian_bridge_collapse&oldid=831198760"