A country’s infrastructure is essential to its success, and having a network of transport systems in place is vital not only for the industry, but for safety too. Bridge construction forms a major part of access routes in every country in the world; from simple wooden bridges in the foothills of rural Wales, to the world famous engineering masterpieces such as the Golden Gate Bridge. The structures may be very different but they serve the same purpose, to provide safe and swift access.
In wealthier parts of the world such as Europe and the UK, the need for bridges is often a matter of convenience, for saving time and improving access and traffic flow from one area to another. In more remote parts of the world, bridges can form a vital connection to essential supplies, and without them certain sections of the population would be at risk in the event of a natural disaster or during times of conflict.
For example, during a study of the Turkish infrastructure, it was noticed that a fault line separated the country along what happened to be an economic divide. In the event of an earthquake this would endanger the lives of some of the poorest of the population as there would be no direct route for supplies and aid. This study led to the construction of a bridge that would ensure that such help would be able to reach these areas should such a disaster occur.
Designing and constructing any bridge is a feat of engineering excellence, but building bridges to withstand the rigours of some of the toughest natural environments is a marvel all of its own. Hurricanes, extreme tides, earthquakes and tornadoes are all elements that need to be accounted for when designing a bridge, and do not forget that human error needs to be accounted for too.
Some of the most notorious bridge disasters involve collapse due to impact from boats and trains. In these accidents, the piers or pilings have given way from the force of the collision and caused the rest of the structure to give way. Other bridge failures have been blamed on superstructure failure due to bad workmanship, such as poor welding, or the use of low quality materials. The final way that bridges can fail spectacularly is in the miscalculation of sums by the engineers themselves.
The mathematics involved in bridge construction involves complex equations that have to account for natural variations in the properties of the chosen construction materials and the way these materials will function in the chosen environment. Add this to the effects of a speeding train, hundreds of vehicles or the marching feet of pedestrians, and the numbers in bridge building become very complex indeed. Many bridges that have appeared structurally sound on paper have behaved in a very different manner in real life.
Some of the most spectacular of these bridge failures have been attributed to what is known as a sinusoidal wave which causes harmonic motion. There is well aired footage of the Tacoma Narrows Bridge which collapsed after the not so harmonic motion caused total structural failure. Basically, small vibrations caused by movement on the bridge accumulate until what appears to be a solid structure has a fluidity that resembles the movement of a wave in water. In some cases, this movement subsides if the causes of the vibrations cease, but in other cases, once the process is underway, the movement becomes self- perpetuating until collapse occurs.
A similar occurrence happened when the Millennium Bridge was opened to the public in 2000. As pedestrians crossed the river the vibrations of the footsteps caused the bridge to sway slightly, and as it did, those crossing had a tendency to walk in time with the movement which served to feed the harmonic motion. Fortunately the bridge was closed without there being any injuries, and over the course of a couple of years the design was modified slightly to prevent such an event happening again. The conclusion is that there will always be a fine balance between engineering genius and pushing the limits of physics itself whilst engineers strive to provide easy or essential access to remote areas and popular destinations alike in the name of technological advancement.