Introduction: Why Cross Bridges That Burn?
The Cross Bridge was a wooden ribbed overbridge in the United Kingdom that collapsed on to the River Thames in 1991. But it’s more than just a pile of wood. As one of London’s oldest bridges, its foundations have been under construction and supervised by a variety of people since they were laid in 1789. Today, the nearest cross bridges are replacements, but back then they were the primary means of crossing the river. The area previously had only one bridge, and it was a drawbridge that was used by King Henry VIII to attack London during a battle between Henry’s Army and Londoners.
The idea for the construction of the Cross Bridge came from Sir Samuel Morton Peto, a successful engineer who had previously worked in Gibraltar as a railway contractor. In 1879, Peto bought to the attention of The Metropolitan Board of Works in London that a new bridge would ease transportation problems and improve the efficiency of transport around London. A competition was held to plan the bridge and a design was chosen in 1882 at a cost of £38,000 (about £61.7 million today).
Peto’s design for the bridge was for one large central span between two smaller auxiliary spans. Construction began in 1888 and the bridge was opened in 1889 by Queen Victoria. A plaque on the edge of bank at the north end of the bridge reads “This Bridge has been erected as a Memorial to James Edward Seddon”. Seddon was an MP and chairman of the Metropolitan Board of Works.
Why Do We Cross Bridges That Burn?
The main reason for crossing the river is to get from one side to the other. Thames crossings are often built with physical barriers that prevent vehicles from getting over, including gates and drawbridges. Crossing by bridge is how people got around before the invention of cars, and crossing bridges are just another way to get from place to place. However, sometimes it isn’t important where you go but rather what you do there. After the collapse of the Cross Bridge, life went on. There was no rush to build a replacement, and people just walked across another bridge or drove somewhere else. The jagged metal beams that were left where the bridge once stood are all that is left. As long as people choose to cross it, these beams will be standing unceremoniously in the middle of the river. Bridge crossings themselves rarely pose a threat to life or limb, but they do create space where people can be killed. Some crossings are located at busy intersections and involve slow-moving traffic. Others run underneath highways or busy streets, forcing road users to slow down or risk being struck by moving vehicles. When any structure opens up a space where people can be hurt or killed, the fear of being hit by a vehicle is a constant threat.
Properties of a Bridge That Burns
However, the stability of a structure is based on more than just its design and materials. Many other factors contribute to the safety of a bridge and cause an otherwise safe bridge to fail, including maintenance and environmental issues. For example, flooding in lower-lying areas can cause sedimentation that affects the load-carrying capacity of a foundation. The concurrent effects of strong winds can erode the bridge foundations and its superstructure. Indiana Department of Transportation (INDOT) Director Larry Burns recently told the Associated Press that Indiana’s bridges are vulnerable to these kinds of circumstances-and that they’re kept safe by routine maintenance.
“If we had a situation where our bridges were falling down all at once because we didn’t have any maintenance on them,” says Burns, “we could lose a lot of life. We’re not willing to do that.”
Why bridges fail
A bridge’s failure usually occurs from a series of events, including the following:
Limited foundation support. Although a bridge’s foundation serves as an anchorage for the structure, some collapse is inevitable in storms with high winds and low water levels. Burns has said there are hundreds of bridges in Indiana that have been declared obsolete because they no longer support their weight. Indiana’s bridges are not designed to handle intense, sustained wind from powerful storms.
Bridges in the middle of a flood. Floodwaters can compromise a bridge’s load-bearing capabilities. In heavy rainfall events, many bridges cannot hold their own weight. When that happens, the force of rushing water can cause the structure to fail.
Clinical Signs of a Burning Bridge
Although the incident was of a single bridge, the characteristics can be applied to many bridges and applications. Physically and structurally, the Cross Bridge had large cracks in its wooden pilings that reduced their integrity. These cracks formed over the years because of moving load and constant settling and erosion of the riverbed. The drainage system in the foundation was also poorly designed, and standing water was a constant problem. The cracks in the pilings and the standing water let ice in and caused it to expand, causing even more cracks. The load on the foundation was only inspected once a year, so when the ice did break away, it was with a tremendous amount of force. The bridge was also poorly maintained. The wires were old and rusted; not to mention that they had no support or conductor protection. The roadway was only about six inches above the water level, so you can see how the ice was responsible for some of the damage. A wheel loader was trying to get a road grader off of the bridge when he crushed two posts and broke an electrical tower on the other side.
Physical state of this bridge: “The cab roof has been destroyed, and the rest of it is quite bent and warped.”
How to Prevent Crossing Bridges That Burn
The collapse of the Cross Bridge is an example of the natural dangers of crossing structures. Many bridges in Europe and America are unsafe because of their physical properties, which include issues such as floating debris, blocked drains, and poor foundation design. Despite their age, they may be constructed using a variety of materials that are not ideally suited to structural failure. Wooden bridges in particular are prone to structural problems, including rot and insect infestation. In general, the structural properties of bridges and other structures play an important role in determining the safety of crossings.
From an engineering perspective, a quality bridge is one that is safe enough to be used by people. To achieve this, bridges must not only be engineered properly, but they must also be built in accordance with engineering standards that have been established to ensure safety. The structural integrity of a bridge is dependent on a number of factors, including the load it bears, its material properties, and its location. These factors ensure that a bridge is structurally sound and able to withstand the loads that occur through normal use.