Wednesday, 31 May 2017

06 - About the dark side of bridge engineering

As I promised you – few decades ago – in this post I'm going to show you some examples of sad accidents involving bridges. I collected some data from the news about bridge collapses during the year of 2016. I'm sure I cannot present here an exhaustive list – I'll only talk about 18 cases in the following –, so please feel free to share in a comment if you know other accidents that I miss to report. 

To be honest, it's a very sensitive topic for me as an engineer. Of course you always want to design the best and safest structure but 100% safety does not exist. There are always (combination of) events that cannot be foreseen and so many people (and machines) are involved in the design and construction of a bridge, that it's impossible to avoid all the smallest errors that may lead to an accident in the future. There are also some decisions that simply do not depend on engineers. For example: at what point should we close a bridge during an extreme event? Or what to do when the bridge reaches the end of its design life? Can we, in any case, compromise on safety? I don't think so...  

So let's see how 2016 went in terms of 'safety of bridges'...

From this pie chart you may think that the bridges of Europe are the most dangerous ones in the world, but I would rather say that the accidents in Europe are better reported and the information is more accessible (at least for me). However we can say that the 'sample' is quite representative in terms of location.
Most commonly the accidents involved road bridges, like highway overpasses for example. I also found a couple of examples for pedestrian bridges, however railway bridges seem to be the 'safest'. This can be due to the higher consequences of a railway bridge collapse they have priority in terms of inspection, maintenance and repair. 
In 1/3 of the cases the accident happened during normal conditions, when bad quality construction materials or bad maintenance strategies could be blamed. However another 1/3 of the cases the accidents were directly related to heavy rain and/or flood of the river underneath the bridge. In the last 1/3 of the cases the collapse happened already during the construction, or it was induced either by a truck hitting the bridge or an overloaded truck passing over. 
It wasn't easy to find some information about the age of the collapsed bridges. In the news the age is very rarely mentioned. However in  a quite large number of the cases the bridge was either still under construction or was just inaugurated recently. In general we can say that the construction phase is a particularly dangerous period of lifetime of a bridge...
This is the hardest part. I don't want to quantify and compare the loss of human lives, so I just wanted to show the proportion  between the accidents that caused fatalities and the ones that didn't. You can see that in more than 1/3 of the cases the bridge collapse did lead to loss of human lives. In the 18 reported accidents in total 200-250 people were injured and 55-60 people lost their lives. 

Finally you can find details about these accidents here:

I know that 100% safety is just a dream, but I also believe  that some of these accidents could be avoided or the consequences could be decreased. This is one reason why I think TRUSS and other research projects focusing on the field of safety and reliability of structures (e.g. Infrastar) are really important...

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