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Sunday, October 3, 2010

What we learn from the history in the design's mistake!

What we learn from the history in the design's mistake!

I’m going to make a couple of points today. First of all, when you are new to civil engineering and first learning to calculate things like concrete columns and roadway curves, it can seem like everything that is in the real world is over designed. There are many rules and regulations that must be followed in your designs. My second point is about engineering ethics. All of the rules can’t cover everything.
Tacoma Narrows Bridge

Every civil engineering student gets to see the one of the videos of the Tacoma Narrows bridge collapse. I was shown this video in three or four different classes in school. If you haven’t seen the video here’s one I found on YouTube. This one is in color and has some additional information.
As far as I’ve been able to find out, the engineers followed the standard rules of the day. By their calculations the bridge should have been fine. But it wasn’t. It collapsed four months after being finished. The engineers fail to account for wind. In a lot of ways, because of this bridge, we have to take into account aerodynamics when designing virtually any structure. Not just aerodynamics, though, we as engineers need to take into account every potential source of forces that may affect our structures.
I 35W Bridge

Here’s a video of the I 35W bridge collapse in Minnesota. This bridge had held well for many years. The initial design could handle the current expected loads. However, later engineers didn’t fully account for additional loads from improvements to the bridge. Specifically, it appears that the gusset plates didn’t have a large enough safety factor. More information on the cause can be found in this article about the University of Minnesota’s Independent Study. According to the study, in addition to the gussets and later improvements, temperature changes played a large role in the collapse. These kinds of things should be considered in an original design. They also need to be double checked when making improvements.
Cypress Street Viaduct
This third video has two parts. One is about the Cypress Street Viaduct and the other about a dam at a coal mine. The Cypress Street Viaduct is another bridge that collapsed due to greater than expected forces. In this case an earthquake. The bridge was designed to easily handle the vertical loads, however they didn’t account for the lateral loads caused by an earthquake. They really only considered enough lateral load to handle wind.
All three of these videos show reasons that we have some of the design standards that we do. We have to include all of the forces that will act on the structure. Not only the everyday forces, but also expected maximum forces. Then we add a safety factor on top of that to take into account anything we didn’t think of.
The second half of that last video adds something else to this. The dam collapsed even though engineers at the time knew how to construct a safe dam. At the time, however, there were no regulations on this type of dam. To save money no engineering was actually done, and no standard maintenance or construction standards were followed. This resulted in the dam collapsing. What this means to us as engineers is that even if there isn’t a law saying that we have to do something a certain way, we should still do it the right way.
Engineering ethics is extremely important to civil engineers. This is one of the few industries where people can get seriously hurt or killed if we don’t do things the right way. Because of that, follow the law and approved standards. If they don’t provide enough guidance then use your engineering judgment and the experience of experts to do the right thing.
Have you had any experience where the standards didn’t meet the needs of you project? What kinds of things have you seen?


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