Cause of Minnesota Bridge Collapse

My dad may be retired but he is still a member of ASCE, the professional society for civil engineers. He forwarded a copy of the urgent e-mail sent by ASCE to all members about the cause of the collapse of the I-35W bridge in Minnesota last fall that killed 13 people.

The collapse was due to a design error, not corrosion or maintenance problems that were assumed to be the problem during the discussions immediately after the disaster.

You can read the NTSB Safety Recommendation Letter and a detailed interim report by two engineers with the Federal Highway Administration on one specific part of that bridge design on the web. Links to these reports are also prominently featured on the ASCE web site.

It is unclear if the undersized plates used at two key joints were the result of a calculation error, an error in developing the plans, or even a drafting error. The documentation on file is still unclear at this point. What is clear is that you don't need a computer to do the calculation, one part of which would be a basic PHY2048 problem. What is important is that, wherever the error was made, the fact that this error ended up in the final plans indicates a significant error in the design process and a failure of the review process used by the engineers responsible for the design. The design review process itself, particularly when renovations are made to an existing bridge, has become the focus of the investigation.

Speaking of presentations, I'd love to hear one of our alumni walk through the part of the calculation I know nothing about, the stress calculation and the treatment of rivets in the net force and torque calculation.

The most striking thing to me was the similarity between the way they presented their results and the way the West Point Bridge Design computer program works to highlight strong and weak points in a design, although this particular design element is not part of the simple bridge designs used in that program.