The Infrastructure is Crumbling, but Don't Panic

As a Montreal resident, I sometimes wonder if the roads are as bad in other major cities.  It seems as though the roads within the province of Quebec suffer from a contagious disease constrained within its borders.  The disease transforms an otherwise developed nation into Colombia with snow.

The moment you cross the border into the United States, the crater-sized potholes vanish and the uneven surfaces become smooth.  If you listen closely, you can hear the suspension system of your car breathe a sigh of relief as you leave Quebec.  If you happen upon a road imperfection while driving in the states, it will be most certainly preceded by one or two warning signs.  If every hole in Montreal's roads were well-marked, there would be no space left for the speed limit signs (which we don't follow anyway, but that's another story).

In truth, dodging potholes and bouncing around in one's car is part of the quebecois experience; the locals have grown accustomed to it.  What the public will never come to accept, however, are falling overpasses and tunnels.  Over the past five years, several such incidents have occurred in the city of Montreal.  In the summer of 2011, reports of a major structure crumbling in some way seemed to become a weekly tradition.  Due to the local media coverage of these incidences, the average Montrealer now knows what a gusset is, and could probably submit a decent draft for our next bridge's design.

Let's first examine why structures fail, and then look at why so many are failing these days in particular.

Applying a Safety Factor in your Life

Nearly all engineering designs serve a purpose.  When they fail to serve the purpose for which they were designed, they are considered to have failed.  Failure is an expectation, as nothing has an infinite lifetime.  As such, all engineering designs have an expected or intended lifetime after they are built and delivered, which may be thought of as a best-before date. 

Things with moving parts, like cars, may have a lifetime of fifteen years and 200,000 km.  That is because a very popular mode of failure is fatigue.  The strength of a material actually decreases when it is stressed, even at low values.  On the other hand, static objects, like chairs, tend to survive longer than is required – typically, the paint will fade long before a leg breaks.  A chair tends to go out of style before it falls apart.  This is not surprising: whenever it is possible, engineers apply a high safety factor to their designs.