Complaceny in engineering, updated.

Grave consequences of engineering complacency in failed Florida bridge.

Introduction

Progress of science and technology is making us much more successful in engineering. As occurence of catastrophic failures become rarer, the human nature of complacency kicks in.

I would like to build on my article "Complacency in Engineering and Learning from Mistakes" with an update and additional content.

The magnificent dome of the Hagia Sophia in Constantinople located in the historic center of current day Istanbul served as a great challenge to the great mind of engineers and architects until modern times. Hagia Sophia has a main span of around 31 meters. Although damaged several times, the dome built by the nephew of the architect Isidoros the Elder, “Young Isidoros” as entrusted with the work by the Emperor Justinian still stands strong after 1500 years!

As technology made feats like 31 meter clear spans a more common achievement, complacency began rearing its ugly head.

Complacency in Action

The bridge as designed

The bridge as designed.

The pedestrian bridge’s main span of 53 meters (174 ft.) and an adjoining span to make a continuous bridge of 88 meters (~289 ft.).

Although I would not be repeating the entire incident report here but I would like to highlight the following in the timeline of events leading to 6 fatalities and 10 non-fatal injuries.

Structural Engineering Basics: Continuity in Structural Members

Civil Engineering and all construction endeavors rely on the basic principle of continuity of materials. Materials transfer loads through a continuous path. The load follows a continuous path until it is transferred from a structural member to another member or surface with sufficient bearing capacity.

It should be noted that cracks in a structural material mean that there is no continuity in that material. It also means that the continuous portion of the material has decreased, meaning less load can follow the path, meaning the overall bearing capacity of the member is decreased.

Armed with this basic knowledge, the following quote from the incident report is quite shocking:

“FIGG hoped that the re-tensioning would either stop further growth of thecracks, or shrink the crack sizes.”

Shrinkage of crack sizes would only make up for part of the lost capacity at best. This “hope” is one of the shocking revelations of the Accident Report [4].

Shocking Series of Events

Another shocking fact omitted from the final report are the text message correspondence among the Engineers working on the project.

Screenshot of text by Kevin Hanson to Sam Nunez showing photos of cracks with the message “It cracked like hell”.

I will refrain from reproducing the entire content of the reports provided in the references but I would like to note that the investigation report identifies Kevin Hanson as one of the most experienced Post Tensioning personnel in Florida. Despite the warnings, concerns regarding the safety and the structural integrity of the bridge were not addressed.

Conclusion: Complacency from Everyone

The probable causes are given in the Highway Accident Report[4] is quoted below.

Probable Cause

The National Transportation Safety Board (NTSB) determines that the probable cause of the Florida International University (FIU) pedestrian bridge collapse was the load and capacity calculation errors made by FIGG Bridge Engineers, Inc., (FIGG) in its design of the main span truss member 11/12 nodal region and connection to the bridge deck.

Contributing to the collapse was the inadequate peer review performed by Louis Berger, which failed to detect the calculation errors in the bridge design. Further contributing to the collapse was the failure of the FIGG engineer of record to identify the significance of the structural cracking observed in this node before the collapse and to obtain an independent peer review of the remedial plan to address the cracking.

Contributing to the severity of the collapse outcome was the failure of MCM; FIGG; Bolton, Perez and Associates Consulting Engineers; FIU; and the Florida Department of Transportation to cease bridge work when the structure cracking reached unacceptable levels and to take appropriate action to close SW 8th Street as necessary to protect public safety.

As seen above, everyone involved ultimately contributed to the failure of the structure, the collapse of the bridge and ultimately the death and injury of 16 people.

References

  1. A. Gulabi, Complacency and Learning from Mistakes, https://www.linkedin.com/in/abdullahgulabi/detail/recent-activity/posts/
  2. S. Engül, The Collapse of the Dome of Haghia Sophia, https://istanbulclues.com/hagia-sophia-dome/
  3. Investigation of March 15, 2018 Pedestrian Bridge Collapse at Florida International University, Miami, FL. US Department of Labor, Occupational Health and Safety Administration, Directorate of Construction, July 2019. https://www.osha.gov/doc/engineering/pdf/2019_r_03.pdf
  4. Highway Accident Report, Pedestrian Bridge Collapse over SW 8th Street, Miami, Florida March 15, 2018 https://ntsb.gov/investigations/AccidentReports/Reports/HAR1902.pdf