Sometimes something that was built before fails, and Engineers have to figure out why
Sometimes things go wrong. Sometimes bad things happen, and a structure or machine fails. Then engineers have to figure out why. We hear about accidents like this in the news. We want to know what went wrong with the machine or structure, so we can make it safer. For example, a building or a bridge might collapse, or a plane might crash, or an offshore oil drilling platform may have an explosion. These things are very rare, but they have all happened at some point in time, and various types of engineers had to figure out why.
To figure out what happened, Engineers look at possible problems, like design, materials, and maintenance
In the case of this bridge, they had to look at whether the bridge was holding more weight than it was designed for. Or, if it had some maintenance issues, like cracks or wear that had gone unnoticed. Or, if there was a problem with the way it was designed, or with the materials used.
When Engineers look at a problem like this, they do not just want to understand this one failure. They also want to know if there are other similar bridges that might be at risk of the same type of failure. If they are, then there may be some work to make other bridges safer - in order to prevent another failure.
If the failure was a design problem, they will look at similarly-designed bridges to figure out what to do. Or, if a particular material or part used on the bridge turns to be the problem, they will look at other bridges using that material or part. If maintenance practices for that type of bridge were the problem, then maintenace practices for similar bridges may need to be different. In any case, the engineers are not just thinking about what went wrong with the specific thing that failed, but also what it means for similar things built elsewhere.
Failure Analysis is about finding out what went wrong, and what can be learned from it
After a long investigation into this particular bridge collapse, engineers concluded that there was a design problem. They determined that some supporting elements, called "gusset plates" were too small. Over the years, layers and layers of concrete had been added, making the bridge heavier. On the day it collapsed, the bridge was really heavy, with construction trucks and rush-hour traffic. That weight on the bridge at that point in time was enough to expose the design problem.
Failure Analysis is a series of steps to find causes for failure in a product, device, or structure, and how to correct or prevent them
In Failure Analysis, Engineers investigate why something failed, and what can be learned from it. There are lots of examples of past failures that have been investigated. Other examples include the Deepwater Horizon oil spill in 2009, the collapse of a garment building in Bangladesh in 2013, and the catestrophic failure of the Fukishima nuclear power plant in Japan in 2011 after a huge earthquake. Figuring out why things failed is an important part of making things safer. And the engineers that figure those problems out have important jobs that make a difference in the world we live in.