Mechanical Engineering (News Analysis)

Introduction

Many people including myself travel over bridges each and every day without giving it a second thought. Recently though bridge failures have been in the news which is something many of us would prefer not to hear. One of the most recent bridge failures happened back in May of 2013; when a bridge in Washington state collapsed. Though no one was hurt in this incident, but it brought back many memories of the 2007 bridge collapse of the I-35 bridge. 

The Article
An article by Fox News titled "Washington bridge collapse caused by truck hitting span, authorities say" was written on May 24, 2013 (Author not given). This is a good article to analyze for mechanical engineers because the article was written using facts that can be proven or statements from people that are involved with the bridge collapse. The article on the I-5 bridge collapse was written days after the event and only presents what had happened and the early thoughts officials have on why the bridge collapsed. The article uses logos (logic) and tends to stay away from emotions or ethics so I believe it is a good article to demonstrate how mechanical engineers are looking at this tragic event.

Background Information

The bridge that failed in Washington state was the interstate 5 bridge that connects Seattle to Canada. This bridge was constructed in 1955 and up to this point in time had not had any issues. The I-5 bridge on average supported roughly 71,000 vehicles a day, many of which were on their way to Canada. The I-5 bridge collapsed into the Skagit River where rescuers quickly responded and pulled three people from their cars following the bridge collapsing. Due to the bridge collapsing traffic issues became a concern between Seattle and Canada with the upcoming Memorial day just a couple days away. With the collapse of the I-35 bridge, many bridges were inspected and their safety was brought into question. The I-5 bridges safety was one of those bridges that received a sufficiency rating of 47 out of a possible 100. Even with this poor rating the bridge should not have collapsed like it had.

Reasoning

Many questions were raised once the survives were rescued and everyone was safe. First was how could another bridge collapse on its own? Did the gusset plates fail again? Could a rating of 47 been wrong and in fact the bridge was in worse shape than originally thought to be?  The first question to be answered was that many people thought that the gusset plates had failed again, well this was a false statement. The section of the I-5 bridge is a different type of bridge compared to the I-35 bridge and the gusset plates should not have been a factor. With the collapse of the I-35 bridge many bridges were inspected to make sure that no other incidents would occur. With this mass inspection of bridges many were found to be in poor condition but all were given a good enough rating to continue to be in service. In fact many people believed that the inspectors were rating bridges on the cautious side and giving worse ratings for bridges than they actually deserved so the rating of 47 should have been a sufficient rating for the bridge and it should not have collapsed on its own. Investigators got their answer as to why the bridge collapsed shortly after starting their investigation. A tractor trailer (Semi) with an oversized load was at the scene when the bridge collapsed. The early report states that the tractor trailer with it’s over sized load struck an overhead beam thus causing the bridge to fail and collapse. This eased many people’s minds knowing that it was human error instead of a design flaw; but it has had an impact on the civil and mechanical engineering fields.

Impact on ME's

This incident has had some impact on both civil engineers and mechanical engineers. Bridges and structures in general are built with a factor of safety so that even with the structure being hit it should not fail. So why did the I-5 bridge collapse? The answer is rather obvious, with the structure receiving a rating of 47 the design engineers never took into account about the age of the bridge and the wear factor that 58 years had on the bridge. With this incident and previous incidents many mechanical engineers are working to ensure that they will not happen again. With new technology and metal alloy blends becoming available mechanical engineers are looking into material that will hold up to the wear and tear of being out in the elements for 50 plus years. Mechanical engineers are also looking into how the factor of safety changes with time. It has become obvious that the factory of safety used for this bridge did not take into account the age of the bridge; so with each incident mechanical engineers are using computer software to help understand how to design and build a better structure with materials that will last.