If ever there was a reminder of the deadly serious nature of civil engineering, March’s bridge collapse in Florida was it.
Six people were killed, including one construction worker, when the under-construction Florida International University bridge collapsed onto the Interstate highway below. Engineers were working on the bridge’s post-tensioning bars at the time.
Many questions are now being asked of the bridge’s design, construction methodology, workmanship and on-site supervision – all areas that could have played a part in the collapse. And with the whole event caught on video camera and much information on the structure’s design already in the public domain through social media, there is plenty of evidence for bridge design experts seeking answers to these questions to go on.
So while the official investigation continues, early theories about the sudden explosive failure of a critical bottom node due to the stressing of post-tensioning bars in possibly poorly compacted concrete through an area that is highly congested with reinforcement and drainage ducts seem a sound starting place.
The bridge collapsed onto a live highway
Two of the first questions asked were, of course: why was this work being carried out over a live highway? And would such a thing ever happen in the UK?
Leading bridge engineers who have spoken to New Civil Engineer have been quick to point out that such an event would be extremely unlikely in the UK; CAT3 bridge checking should pick up design deficiencies; extensive tests and mock ups would have ensured the correct concrete mix; and strict rules would have ensured the that highway was closed before work was carried out on sensitive elements such as tensioning bars.
But there’s more to it than that. This is a terrible, tragic incident made all the more so by the fact that the project team was trying to innovate. Much was being made of this on social media in the days leading up to the collapse. This was, we were being told, a pioneering use of the university’s own Accelerated Bridge Construction Methods, methods designed, said the university, to “reduce potential risks to workers, commuters and pedestrians and minimise traffic interruptions”. A key part of this was offsite construction, with the deck component lifted into place just days before the collapse.
It was also to be the “first in the world to be constructed entirely of self-cleaning concrete”, using titanium dioxide in the mix to keep its surface clean by catalysing the UV breakdown of pollutants. It is perhaps worth asking how well the project team understood the properties of this special mix.
So it again raises that huge question about innovation. UK public sector clients have for years been lambasted for their reticence to embrace innovative materials and methods. Indeed, the industry’s perceived reluctance to embrace techniques such as offsite construction is routinely touted as the reason for the industry’s poor productivity. Clearly we do not yet know if the innovative materials or methods were responsible in Florida. But you can bet that UK client technical teams are now going to be on high alert. They should be.
We need to innovate as an industry. But we also need to be ever aware of the safety implications of what we do. As we also report this month, workforce safety performance of the UK construction industry is getting ever better, with technology accelerating this improvement.
But what of the risks to the public? It may be the Florida bridge collapse necessitates a new chapter in ICE’s post-Grenfell review into the risks of infrastructure failure. It will surely makes it all the more essential reading when it lands. Watch this space.
- Mark Hansford is New Civil Engineer’s editor