There are many professions that can have a tremendous impact on the lives of others. Engineering is one of these. When done correctly and professionally, engineering can enhance the lives of people throughout society. However, if it is not done correctly and professionally, then it can lead to tragedy for many. Engineering failures often make the news for a reason: they can have deadly results. Even without the tragedy of death and injury, it should be noted that they often involve significant amounts of money. The money and resources were wasted, something that society cannot afford in the modern world. One of the failures of modern engineering occurred on the bridge on I-35 Westbound in Minnesota. This collapse was truly tragic because it cost the lives of thirteen individuals. It also injured one hundred forty-five people. It failed due to a design collapse (Minnesota Public Radio).
The bridge collapsed on August 1, 2007. It failed under the weight of rush-hour traffic. The failure in design clearly violated the ethics of engineers. According to the Code of Ethics of the National Society of Professional Engineers, engineers must “hold paramount the health, safety and welfare of the public.” Since the construction was flawed, the company and its engineers failed to do this. Furthermore, there were multiple warning signs that this bridge would fail. Not only were they not addressed, but some work actually increased the dead load of the bridge, increasing its risk of failure.
The design of the bridge was flawed. This was discovered several years before the failure. The bridge was a truss design. A truss design works by the connection of multiple triangular-shaped units to support the structure. The design can be quite effective, as well as cost efficient. However, if one part of the unit fails, the entire structure fails. There is no redundancy in the structure to overcome the failure of one part (Wald). This is the most concerning aspect of truss construction. In order to combat this, it is crucial to ensure gusset plates that can support the structure. The structure failed because the gusset plates were undersized. Furthermore, an additional two inches of concrete were added to the bridge over the course of time; this increased the dead load of the bridge by 13.4%. The gusset plates were not even adequate to hold the original dead load of the structure (National Transportation Safety Board).
There were multiple warning signs that the structure would fail. However, these were ignored. An inspection in 1997 indicated that there was bowing to the gusset plates. However, the person who noted this did not believe it was a problem; he believed that, based upon his undergraduate education, gusset plates are overdesigned for safety. However, these ones were tragically under designed for the size of the bridge. He also believed that there were no other signs that the structure was in danger. An inspection in 1998 indicated that there were problems with the structure. While the structure was built according to 1961 specifications, it did not meet current specifications. Changes to the median increased the dead load by another 6.1%. The bridge was currently nearly twenty percent over its designed-for dead load (National Transportation and Safety Board 60-65).
Obviously, the collapse of the bridge could have been prevented, and with it the fatalities and injuries associated with it. Better systems need to be designed to track changes to the structures of bridges. This includes new calculations of dead loads with any major repair work done on the structure. It also should require a computerized simulation of all structures. These simulations can be updated as additional changes are done on the bridge. It can also include the requirement of an inspector to note any deficiencies noted on the structure. If these are placed into the system that can simulate the actual effects, the computer simulation may flag a problem. Obviously, sincer truss construction does not have redundancy in it, then inspections of truss structures must be redundant. Two engineers should be required to sign off on any deficiencies that are noted during an inspection. If two of them had to review the information on gusset plates, both may not have been so trusting that the correct size and width of gusset plates had been used in the original construction.
The problem in the construction was that many engineers did not appear concerned about the problems. If multiple problems had been noted in the years before the collapse, they should have been taken more seriously by the engineers and the inspectors. It is difficult to place blame on one person. By all means, the original blame belongs to those who designed and constructed the bridge. Using an incorrect size of a gusset plate is simply unforgivable when designing and constructing a truss bridge, or any structure that utilizes a truss. Truss structure failure is a noted aspect of the design. It is crucial to ensure that all of the features can support the dead load. It was also careless of the engineers who approved the concrete. They did not appear to recognize that two inches of concrete is several million pounds on a structure. Furthermore, the repeat inspections were poorly done. If any problem is found with a bridge, it should be immediately reported. All of these individuals share some of the blame.
Engineering failures happen. They are part of history. From the Leaning Tower of Pisa to the famous “Galloping Gertie” bridge, they represent the human failure aspect of construction. However, it is not enough to say that “humans make mistakes.” Yes, they do. That is why there should be multiple levels of protection built into the system. Again, since a truss design lacks redundancy, there should be multiple levels of redundancy on its inspection. If a computer simulation must be used and updated with any changes or problems in a bridge, it may also help to alert the engineers about any problems.
- Minnesota Public Radio. “I-35 W Bridge Fact Sheet.” 3 August 2007. 20 August 2014. http://www.mprnews.org
- National Society of Professional Engineers. “Code of Ethics.” July 2007. 20 August 2014. http://www.nspe.org
- National Transportation Safety Board. (n.d.). “Highway Accident Report.” N.d. 20 August 2014. http://www.ntsb.gov/
- Wald, M. “Faulty Design Led to Minnesota Bridge Collapse, Inquiry Finds.” The New York Times. 15 January 2008. 20 August 2014. http://www.nytimes.com/