Bridge failure don’t occure often but when they do the results are spectacular and unforgettable. once you have seen the footage of the ‘Tacoma Narrows Bridge‘ resonating in a gale, bucking back and forth before the deck breaks up and crashes to the river below you will never forget it.
Bridge always collapse for exactly the same reason. Something happens that makes them unable to balance the forces acting on them. A force becomes too great for one of the components in the bridge ( maybe something as simple as a single rivet or tie bar ) which immediately fails.
That means the load on the bridge suddenly has to be shared by fewer components, so any one of them might also be pushed beyond its limit. Sooner or later another component fails than another and so the bridge collapses in a kind of domino effect of failing materials.
How Bridge Failure Occurs and Precautions to be Taken.
First and simplest it might be too weak to cope with a sudden transient load. If a bridge is designed to carry no more than 100 cars but 200 heavy trucks drive onto it instead that creates a dangerous transient load or if hurricane-force winds buff at the bridge twisting the deck much more than it’s designed to cope with that can be catastrophic too.
So a bridge can fail through weakness because a force exceeds which is called as ultimate tensile strength or compressive strength of the materials from which it is constructed. But a bridge can also fail even if the forces on it are relatively modest and well within these limits.
Everyday materials usually have to undergo repeated stresses and strains for example :- A bridge deck is loaded and then unload it again immediately afterward and that can happen hundreds or thousands of times a day, hundreds of days a year. Just as a paper clip snaps when you repeatedly bend it back and forth, the endless cycles of stress and strain flexing and relaxing can cause materials to weaken over time through a process known as fatigue.
Eventually, something like a metal cable or tie in a bridge will snap even though it’s not experiencing a particularly high stress at that moment. Fatigue is often compounded by gradual corrosion of metal components or what’s informally known as concrete cancer.
Engineers try to protect against bridge failures in two main ways. If we learn to see bridges as living structures constantly aging and being degraded by weather and the environment, its easy to understand that they need regular maintenance just like our homes and bodies.
Periodic inspections and preventative maintenance helps us spot problems and correct them before it’s too late. Engineers can also protect against bridge failure by building in a factor of safety. Designing them so they can cope with forces several times larger than they are ever likely to encounter, that might include extra redundant components for reinforcements so that even if one part of the structure fails others can safely share the load until the bridge can be reinforced or repaired.