When the dimensions and scales were drawn and the location to where the bridge should be built was clear, the Tacoma Narrow Bridge seemed to be the best thing to happen in Washington connecting Seattle and Tacoma with the Puget Sound Navy Yard. It had a center span of 2,800 feet and a 1,000 foot approaches at each end. This made the planning and scope appropriate time to start the project.
The planners began taking unknowing and unnecessary risks when they notice that the bridge began swaying from just a slight current of the wind that blew. It was to withstand a current of wind at 100 miles. However, it did not as it went into a violent vertical and torsional oscillation.
The constraints aspect of the project was that as the winds increased, the more the bridge seemed to come alive and literally shook itself apart. As the winds blow harder, the bridge was reaching a roll of 45 degrees in either direction causing the bridge to rise and fall over 30 feet.
I don’t think that all these issues where taken into consideration because new things come about year after year with new codes. This was built back in the 50’s and the way everything was looked at, and the designed, the dimensions, it seemed to be a likely project that would last a lifetime.
The construction of the Tacoma Narrow Bridge predates most of the more sophisticated methods available today. The answer is that they did not recognize the qualitative risk in the design, sighting of the bridge, or construction until after it had been constructed, because of a quantitative risk analysis method or the lack of it.
The form of risk mitigation is that the theoretical knowledge base underlying a design is weak or incomplete; it must be supplemented by an adequate base of experiential knowledge. If the experiential knowledge base is weak or incomplete it must be expanded until it is adequate. A principal way of practicably doing this is through appropriate modeling. In the example of the Tacoma Narrows...