Re: Are there any particular reasons why a bridge would fail?

Hello Katherine,

I'll be answering your question as an Architect (as opposed to an engineer). Until recently, bridge design was the undisputed domain of the engineer. However, as engineers have been increasingly concerned with design codes, aesthetics and material and structural specifications, architects have become more involved in the creative design process. Typically, the architect develops new concepts and forms while the structural engineer ensures the structural rationality. For this balance to work, there must be full design collaboration between architect and engineer.

Bridges must combine simplicity, functionality (SAFETY), economy and environmental harmony. There are several basic bridge types (arch, span, suspension, or combination). We have become pretty good at estimating material capabilities and structural requirements in order to construct a safe bridge. Factors that make bridges UNSAFE are those that have not been considered during the design process. Unfortunetely, some of these factors come to light by "trial and error". For example, years ago, a long span bridge failed in Tampa FL after a large cargo ship collided with a main bridge support. This was a catastrophic failure that resulted in parts of the roadway (and vehicles) falling into the bay. As a result, we now construct buffer areas ("bumpers") around these vital supports. Another area that we have made great strides in is earthquake design. We now make sure that the bridge structure can absorb these energies without failure.

For safety, architects/engineers look at:

1. Soil borings - will the soil provide the necessary support over the long term.
2. Geography - are there any ground faults nearby, are conditions stable?.
3. Wind pressures expected - for example, wind pressure within a canyon can reach high velocitys, lateral/torsion support will be required.
4. A maintenance/inspection program is set up in order to verify that conditions remain safe.
5. Environmental concerns have also become more important, this addresses the safety of our non-human friends.

As time goes on, bridge design will continue to improve. Perhaps if you study engineering or architecture, you can design a large beautiful bridge for us. For additional information, refer to some bridge pages at Newton's Apple

Thanks for the question.