Wednesday, March 28, 2018

Miami Florida University Bridge Collapse

Miami Florida University Bridge Collapse --- ===

an anonymous Canadian engineer or contractor has posted a crowd-sourced You Tube video exploring the cause of the collapse that has drawn more than half a million views.

 In the video, the Canadian runs a demonstration showing how a steel rod undergoing tensioning will suddenly snap and shoot out of the jack if ...

Florida International University pedestrian bridge collapse

From Wikipedia, the free encyclopedia
FIU Sweetwater UniversityCity pedestrian bridge collapse
FIU Bridge NTSB inspection.jpg
National Transportation Safety Board members inspecting the collapsed pedestrian overpass on March 16
DateMarch 15, 2018
Time1:47 p.m. EDT
LocationUniversity Park and SweetwaterFlorida, U.S.
TypeOverpass section collapse
Non-fatal injuries9
On March 15, 2018, a 175-foot-long (53 m), recently-erected section of the FIU Sweetwater UniversityCity pedestrian bridge collapsed onto the Tamiami Trail (U.S. Route 41).
The initial construction on the pedestrian bridge was located in front of the campus of Florida International University (FIU) in University Park, a suburb west of MiamiFloridaUnited 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]


The FIU Sweetwater UniversityCity pedestrian 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 (MCM), a Miami-based construction management firm, and FIGG Bridge Engineers, a Tallahassee-based firm.[8] Unlike most bridges in Florida, the design for this project was overseen by the university itself, not the Florida Department of Transportation.
Florida International University is known for its expertise in accelerated bridge construction, and has attracted international scholars as PhD students. It is home to the federally-funded Accelerated Bridge Construction University Transportation Center, which sponsors industry conferences and seminars.[9][10]

Bridge layout[edit]

The full 320-foot-long (98 m) pedestrian overpass was to cross both a major roadway and a parallel water canal with two separate spans connected at a faux cable-stay tower. The main, roadway-crossing span was 175 ft long, the shorter canal span was to be 99 ft long. An elevator and stairs at the south end added 31 ft, and at the north end, 15 feet, for a total bridge length of 320 feet. [11] At the bridge site the Tamiami Trail roadway has six lanes of traffic plus two turn lanes. The main span was rolled into place and set on support columns on March 10, five days before the collapse. The canal span, access ramps, and faux 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.
Elevation Engineering Drawing of Proposed FIU Sweetwater Pedestrian Bridge

Bridge construction and design[edit]

Construction of the bridge began in March 2016 and was scheduled to be completed in December 2018.[7][12] The bridge's main span was assembled adjacent to the highway using accelerated bridge construction (ABC), a technique promoted at the university.[1] It was lifted into place on the morning of March 10, five days before the collapse, during a weekend closure of the highway.[13][14]
FIU-Sweetwater UniversityCity Bridge
Coordinates25.7612°N 80.3728°WCoordinates25.7612°N 80.3728°W
CarriesPedestrian traffic
CrossesTamiami Trail
LocaleUniversity Park and SweetwaterFlorida, U.S.
Total length320 feet (98 m)
Longest span175 feet (53 m)
Engineering design byFIGG Bridge Engineers
Constructed byMunilla Construction Management
Construction cost$14.2 million
CollapsedMarch 15, 2018
University Park is located in Florida
University Park
University Park
Location in Florida
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.[15][16]
The bridge was a post-tensioned concrete structure.[15] Concrete structures are generally 10 times heavier than equivalent steel designs.[17] The bridge was made using a new formulation for concrete intended to stay cleaner than standard concrete formulations.[18]In the main bridge span, the concrete floor deck, roof, and diagonal struts each contained post-tensioning cables whose compressive effect on the concrete could be adjusted after the concrete was cured.[15] Adjustments were expected each time the span was moved onto a different foundation with different support points.
The full bridge project was styled to look like a cable-stayed bridge with pylon tower and high cables for dramatic effect. But functionally and structurally it was actually a truss bridge, with the spans being fully self-supporting.[15][19][20]The bridge spans used a novel concrete truss design invented for this project, a "re-invented I-beam concept". Concrete truss bridges are rarely constructed, and few exist. [21]The vertical web of the beam was a series of triangulated concrete diagonal struts along the centerline. The diagonal angles of the struts varied across the bridge so they would align with the eventual cable-stayed appearance - a feature unique to this truss bridge. Conventional truss bridges use regular repeating angle triangles. A bridge redesign late in the project required moving the bridge’s main pylon tower 11 feet (3 meters) north to allow for future highway widening, increasing the gap between the bridge end supports and requiring some new structural design. It is unknown at this time if the angles of the concrete diagonals or the length of the spans were changed in the redesign.[22]
The concrete walkway deck was to act as the horizontal bottom flange of a wide I-beam, and the concrete roof canopy was to function as the horizontal top flange of the I-beam. [15] The walkway was thus nearer to ground level than in a standard design where the walkway is placed on top of the structural support system.[15] This reduced the number of steps to climb. The deck carries the entire weight of the bridge span, as a tension load. The canopy carries the structure's main compressive loads. The diagonal struts carry either compression or tension forces, depending on their angle and position. The struts contain post-tensioning rods that connect the flanges, and are adjusted as needed.[23] VSL was the company contracted for the post tensioning (PT) of the new bridge. Post-tensioning of a diagonal member may be one of the reasons for the structural failure of the FIU bridge. Concrete is much more prone to crack than steel in trusses. [24]Certain cracks could compromise the cable/rod anchorings, making failure inevitable when the post-tensioning operation began.[25] The bridge was meant to last more than 100 years, and to withstand a Category 5 hurricane, in a statement by the university.[26]


Schematic of the bridge. Green: collapsed parts, Blue: not installed at the time of the collapse. The diagonal beam that was undergoing post-tension cable/rod adjustment at the time of the collapse is highlighted in red.

Reports of pre-collapse cracking[edit]

On 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.[27][28]
At 9 a.m. on March 15, a university employee heard a loud "whip cracking" sound while under the bridge span, waiting for a red traffic light.[29] At the same time, the design-build team met for about two hours at the construction site to discuss the cracks discovered on March 13. 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.[30]
The mayor of Miami-Dade County, Carlos A. Giménez, said that workers conducted a stress test on the morning of March 15.[31]


At 1:47 p.m., the north end of the installed bridge span sagged deeply as the first diagonal fractured, 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.[32]
United States Senator and FIU adjunct professor Marco Rubio tweeted that engineers were tightening loosened cables on March 15:[31] Workers were adding more tension to the steel rod (tendon) inside a concrete diagonal strut at the north end.[27] The National Transportation Safety Board, who are investigating the collapse, stated that crews were applying "post-tensioning force" on the bridge before the collapse.[33]
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.[34] It dropped onto the roof of the bridge next to workers, and where the roof and span broke apart.

The tensioning rod that was being tightened at the time of the collapse, with a hydraulic tensioning machine (blue) still attached to its end, extends from the canopy in the upper left of this image.
At this time, it is not clear why the post-tensioning operation by VSL company was being carried out at the time of the collapse as the bridge diagonal member support they were working on would have already been in compression. A possibility, as reported by New Civil Engineer, is they were trying to put an additional compression into the member to close cracks in the bridge superstructure.The bottom joint of diagonal member #11 (which contains the anchor nut for the post-tensioning rod) apparently failed explosively, during the post-tensioning operation, causing the bridge to collapse.Currently, it remains unknown why the joint may have failed, although post-tensioning remains a possible contributor.[35] A driver who survived the collapse reported small rocks fell onto her car just before the car got smashed.[36] A worker saved himself when he heard cracking and locked his safety harness just before the collapse.[37]
The span that collapsed weighed 950 short tons (861 tonnes).[38]
At the time of the collapse, the roadway was open and there were multiple cars stopped at a traffic light under the span.[39][40][41] Eight cars are reported to have been crushed. Six people were killed and nine others were 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.[42] An employee of VSL, Navaro Brown, 37, worked for the company contracted to apply post-tensioning and died in the collapse. Two other employees of the company were hospitalized. The other deceased victims of the tragedy were identified as Alberto Arias, 53, Brandon Brownfield, 39, FIU student Alexa Duran, 18, Rolando Fraga, 60, and Oswaldo Gonzalez, 57.[43][44][45]


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 Homestead Extension of Florida's Turnpike would be closed indefinitely while debris removal and investigations were conducted.[46] A team of 15 people from the National Transportation Safety Board (NTSB) began their investigation that morning.[47] On March 19, 2018 the first civil lawsuit was filed against Figg Bridge Engineers, MCM, Bolton Perez & Associates, the project’s consulting engineer, Louis Berger, and Network Engineering Services for reckless negligence.[48]


NTSB investigates Miami bridge collapse IMG 0009 (39942593765)
On March 15, 2018 the National Transportation Safety Board (NTSB) launched a Go-team to investigate the bridge collapse incident. The accident number assigned is HWY18MH009. [49] On March 16, 2018 the NTSB Investigators held their first press conference to discuss the inquiry into the bridge collapse. Noteworthy points from the meeting included a statement that the inquiry was in the very early stages, that cracks in the bridge superstructure did not necessarily make the bridge unsafe, that on-site investigations would take about a week, that preserving perishable evidence was crucial, and that bridge workers were applying a "post-tensioning force" on the bridge before the failure.[50]On March 21, 2018 the NTSB sent out the following press release:
Investigators secured a contract Tuesday to have a company remove components from the bridge that we believe warrant additional examination and testing. These components include sections of the floor, the canopy, a vertical member and a diagonal member; all from the north end of the structure. These components were in the area of where the failure occurred. In addition to these components, we obtained additional core samples from this area to supplement the core samples we obtained earlier. Shipping the core samples along with some recovered rebar and tensioning rods to the Turner Fairbank Highway Research Center, in McLean, Virginia, for testing and evaluation. The investigative team has obtained an exemplar tensioning rod and hydraulic unit used by the construction crew to make tension adjustments to the tensioning rods. These items are also being shipped to the Turner Fairbank Highway Research Center for evaluation and testing.The larger bridge components the investigative team is removing, are being stored at a secured Florida Department of Transportation facility, under the control of the NTSB. The additional examinations and forensic deconstruction of these components will occur there. The investigative team has confirmed that workers were adjusting tension on the two tensioning rods located in the diagonal member at the north end of the span when the bridge collapsed. They had done this same work earlier at the south end, moved to the north side, and had adjusted one rod. They were working on the second rod when the span failed and collapsed. The roadway was not closed while this work was being performed.
On March 21, 2018 U.S. Transportation Secretary Elaine Chao asked the department’s inspector general to probe whether a federally funded UniversityCity pedestrian bridge complied with all rules.[51] A subsequent internal memorandum from the Inspector General of the U.S. Department of Transportation, dated March 22,2018 included the following statements[52]:
The Florida International University pedestrian bridge was funded in part through the Department of Transportation’s (DOT) Transportation Investment Generating Economic Recovery (TIGER) discretionary grant program.1 The Federal Highway Administration administered the grant funds for the project. On March 19, the Secretary of Transportation requested that we initiate an audit to evaluate whether the project complied with Federal requirements and specifications. On March 20, Senator Bill Nelson, Ranking Member of the Committee on Commerce, Science, and Transportation, requested that we also review the implementation and oversight roles of all parties on the project. We share these concerns about the collapse, and we are committed to supporting the Department’s efforts to improve transportation safety. Accordingly, the objective of our audit will be to assess whether the Florida International University pedestrian bridge met Federal and DOT requirements for the TIGER application, approval, and grant agreement processes.

See also[edit]


  1. ^ Jump up to:a b c 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. ^ Jump up to: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. Jump up^ "FIU Bridge Collapse: Four Dead, 8 Cars Trapped Underneath". CBS Miami. March 15, 2018. Retrieved March 17, 2018.
  4. Jump up^ Ashaboglu, Selin (March 15, 2018). "Miami Pedestrian Bridge Collapses". ARCHITECT. Retrieved March 15, 2018.
  5. Jump up^ 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. Jump up^ "FIU Pedestrian Bridge Construction Using Innovative Approach By Swinging Into Place". CBSLocal. WFOR-TV. March 10, 2018. Retrieved March 15, 2018.
  7. ^ Jump up to: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. Jump up^ Gomez Licon, Adriana; Replogle, Josh (March 16, 2018). "Tearful families wait as bodies remain under failed bridge". Associated Press. Retrieved March 17, 2018.
  9. Jump up^ Bridge Collapse Saps Spirits and Research Efforts at Florida International University, By PATRICIA MAZZEI and STEPHANIE SAUL, New York Times, March 17, 2018
  10. Jump up^ "Home - Accelerated Bridge Construction". Accelerated Bridge Construction. Retrieved March 19, 2018.
  11. Jump up^ General Plan and Elevation|url= |access-date=March 23, 2018|publisher=Florida International University}}
  12. Jump up^ Kiah, Clara-Meretan (March 30, 2016). "FIU, Sweetwater break ground for bridge to the future". Florida International University. Retrieved March 15, 2018.
  13. Jump up^ Viglucci, Andres (March 10, 2018). "'Instant' bridge aims to make a dangerous crossing safer for thousands of students". Miami Herald. Retrieved March 15,2018.
  14. Jump up^ 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.
  15. ^ Jump up to:a b c d e f MCM. "MCM design-build proposal" (PDF). Retrieved March 18, 2018.
  16. Jump up^ Tylin International (May 6, 2015). "Design Criteria, FIU-UniversityCity Prosperity Project - Pedestrian Bridge" (PDF).
  17. Jump up^ Staletovich, Jenny; Rodriguez, Rene; Flechas, Joey. "Stress test may have contributed to collapse of FIU pedestrian bridge". Retrieved March 18, 2018.
  18. Jump up^ 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?". @FIUnews. Retrieved March 17, 2018.
  19. Jump up^ 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.
  20. Jump up^ FIU Bridge Collapse NTSB Update. Robert Accetta (press briefing speaker). WSVN-TV. March 16, 2018. Retrieved March 19, 2018 – via YouTube.
  21. Jump up^ Bridgehunter. "concrete truss bridges". Retrieved March 21, 2018.
  22. Jump up^ Jason Dearen and Jennifer Kay. "Key design change stymied bridge cost, schedule". Retrieved March 22, 2018.
  23. Jump up^ Jennifer Kay and Allen G. Breed (March 18, 2018). "Bridge collapse victim's uncle rages at 'incompetence'". Chicago Tribune. Retrieved March 18, 2018.
  24. Jump up^ "Pedestrian bridge collapse in Miami, Florida..." Retrieved March 20, 2018.
  25. Jump up^ "A Bridge Too Faux: Florida's Pedestrian Bridge Would Only Have Looked Safe". Retrieved March 20, 2018.
  26. Jump up^ "Collapsed bridge meant to last 100 years".
  27. ^ Jump up to:a b 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.
  28. Jump up^ "Bridge collapse victim's uncle rages at 'incompetence'".
  29. Jump up^ "FIU employee heard a loud crack crossing under the bridge. Hours later, it collapsed". miamiherald. Retrieved March 17, 2018.
  30. Jump up^ Mier, Alyse (March 17, 2018). "FIU statement" (Press release). FIU. Retrieved March 17, 2018.
  31. ^ Jump up to:a b "Rubio says engineers were tightening loose cables when the FIU bridge collapsed". miamiherald. Retrieved March 17, 2018.
  32. Jump up^ "Miami bridge collapsed during 'stress testing' killing at least four". Mail Online. Retrieved March 17, 2018.
  33. Jump up^ "Bridge victim's grieving uncle lashes out at 'incompetence'". AP News. Retrieved March 18, 2018.
  34. Jump up^ "Found Video: Miami Bridge Collapsed During Stress Test Conducted in Afternoon Traffic". Santa Monica Observer. Retrieved March 17, 2018.
  35. Jump up^ Smale, Katherine. "Experts cite explosive joint failure as cause of Florida bridge collapse". New Civil Engineer. Retrieved March 21, 2018.
  36. Jump up^ "At least 4 dead in catastrophic FIU pedestrian bridge collapse; 9 rescued from rubble". miamiherald. Retrieved 2018-03-21.
  37. Jump up^ News, A. B. C. (2018-03-16). "Worker hurt in bridge collapse thinks locking in harness saved his life: Cousin". ABC News. Retrieved 2018-03-22.
  38. Jump up^ Cochrane, Karen (March 16, 2018). "Pedestrian Bridge FAQ" (Press release). FIU. Retrieved March 17, 2018.
  39. Jump up^ 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.
  40. Jump up^ 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.
  41. Jump up^ "Florida Pedestrian Bridge Collapses During Stress Test Conducted in Afternoon Traffic". Santa Monica Observer. Retrieved March 16, 2018.
  42. Jump up^ "Florida Bridge Collapse Moves Into Investigation Phase". The Wall Street Journal. March 18, 2018. Retrieved March 19, 2018.
  43. Jump up^ "Bridge worker Navaro Brown died in collapse of FIU span, company says". Retrieved March 20, 2018.
  44. Jump up^ 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.
  45. Jump up^ "New video surfaces of FIU bridge collapse from view of driver who witnessed it".
  46. Jump up^ "Southwest 8th Street To Be Closed As Bridge Collapse Is Investigated". CBS Miami. March 16, 2018. Retrieved March 16, 2018.
  47. Jump up^ Bowden, John (March 15, 2018). "NTSB chairman: Agency will investigate Florida bridge collapse". The Hill. Retrieved March 16, 2018.
  48. Jump up^ Martin Vassolo. "Survivor of FIU bridge collapse sues design-construction firms". miamiherald. Retrieved March 19, 2018.
  49. Jump up^ NTSB (March 15, 2018). "Pedestrian bridge collapse". Retrieved March 19,2018.
  50. Jump up^ Jennifer Kay and Allen G. Breed (March 17, 2018). "Authorities are investigating whether reported cracking contributed to the collapse of a Florida bridge that killed 6 people". Business Insider. Retrieved March 17, 2018.
  51. Jump up^ Editorial, Reuters. "U.S. Transportation Secretary seeks probe of fatal Florida bridge..."
  52. Jump up^

External links[edit]


Experts cite explosive joint failure as cause of Florida bridge collapse

The collapsed bridge in Florida. On the left hand side of the picture - the north end of the bridge - the bottom of diagonal member can be seen to have pulled away from the bottom critical joint which sits on the top of the pier.

A blue jack still attached to the end of a bar feeding into diagonal member 10 can be seen on the collapsed bridge.

Drawing of the bridge in it's final condition released by the National Transportation Safety Board (NTSB).




The collapse of the bridge in Florida was probably caused by an explosive failure of a key joint in the bridge’s concrete truss, structural engineers have told New Civil Engineer.

The 862t concrete bridge over a highway at the Florida International University (FIU) in Miami collapsed last Thursday killing six people. Investigations are now underway to determine the exact cause.

But structural engineers who have spoken to New Civil Engineer have studied multiple photographs of the scene and believe the collapse was caused by an explosive failure of the north end, bottom joint – a critical connection in the bridge’s structure.

Florida bridge design possible 'recipe for disaster' says expert


The design of the Florida International University (FIU) bridge which collapsed onto a live highway killing six people, could be seen in h
Post Tension Failure Florida Bridge Collapse | Engineering ... - YouTube
▶ 16:13
Mar 16, 2018 - Uploaded by AvETHANK YOU FOR YOUR INTELLIGENT ANALYSIS and WILD-ASS THEORIES! I ran a test to see why the post ...

Engineer Reported Cracks on Miami Bridge Days Before Collapse - WSJ 16, 2018 - Two days before a new pedestrian bridge collapsed in Miami, killing at least six people, one of the project engineers called a Florida transportation official to ... officials, including the Miami-Dade County mayor, said they had been informed that a stress test was being conducted at the time of the collapse.

'I Thought I Was Dead:' Victim of Bridge Collapse Speaks Out - NBC 6 ...
Mar 16, 2018 - The 950-ton bridge was being put to a stress adjustment before it collapsed. A 19-year-old college student who narrowly escaped Thursday's bridge collapse near the Florida International University campus is recalling the moment the massive concrete structure fell and crushed the vehicle he was riding in.

CCTV footage shows moment Florida bridge collapses - YouTube
▶ 1:55
Mar 16, 2018 - Uploaded by Guardian NewsA newly installed pedestrian bridge at Florida International University in Miamicollapsed on Thursday ...

Design of doomed FIU pedestrian bridge was vulnerable to failure ... 20, 2018 - The Florida International University pedestrian overpass that collapsed while under construction was a modern variation of an old bridge design that experts say ... In the video, the Canadian runs a demonstration showing how a steel rod undergoing tensioning will suddenly snap and shoot out of the jack if ... While it will likely be months before federal investigators lay out an official explanation, growing available evidence suggests that failure of a single diagonal support truss at one end was enough to cause the entire 174-foot concrete span to buckle under its own weight and crash onto Southwest Eighth Street near the entrance to Florida International University Bridge engineers not involved with the project have said overtightening of rods or cables that provide tensile strength in concrete slabs and beams can cause the pieces to twist and shatter abruptly.  But an anonymous Canadian engineer or contractor has posted a crowd-sourced You Tube video exploring the cause of the collapse that has drawn more than half a million views. well-known vulnerability: If a vehicle hits one of the horizontal support trusses, the entire span can collapse.

single row might have made the design especially vulnerable. If one diagonal piece failed, it’s didn’t have a twin on the other side that might have provided some support in the same area.  “The unique part is, it’s a single truss,” he said. “When one member failed, there was no redundancy.”

faceless Canadian YouTuber suggests, is that the steel inside the struts could have been damaged. His evidence: photos showing a steel rod protruding from the top of the bridge canopy with a blue hydraulic jack — equipment used in tensioning support cables or rods inside concrete — still attached. A subcontractor crew member working on that spot fell to his death when the bridge collapsed.

In the video, the Canadian runs a demonstration showing how a steel rod undergoing tensioning will suddenly snap and shoot out of the jack if stressed beyond its capacity.

unsupported end could have placed enough stress on the last diagonal strut — the one being worked on when the bridge fell — to damage the rod inside it and loosen the tension on it, the Canadian AvE says in his YouTube video. It would also explain cracking that appeared on the north end of the bridge that a FIGG engineer reported to FDOT on Tuesday, 

.. additional tensioning work being carried out was a result of the meeting, and that routine tensioning or tuning of the bridge had been concluded on Monday, before the Trail was reopened to traffic. 

Fla. Bridge Collapse Probe to Focus on Steel Tension Cables - NBC 7 ...
Mar 19, 2018 - As investigators scour the wreckage of the pedestrian bridge that collapsed near FloridaInternational University, they will likely focus on the steel cables that were being tightened when the 950-ton concrete slab fell onto the highway below, crushing several vehicles and leaving six people dead. NBC 6's ...
Missing: snap

Workers adjusted bridge tension before fatal collapse - NY Daily News days ago - Workers were adjusting the tension of a pedestrian bridge at Florida International University when it collapsed.

No comments:

Post a Comment