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Brief History

• Bridges were simple structures that were built from natural resources because they were easily accessible.
• These natural resources include; wood, stone, and dirt.
• The first bridges could only span short distances as the structures were not that strong as they used dirt in place of mortar as it was not invented yet.
• In Ancient Rome it was discovered that grinded out volcanic rocks were good material for making mortar.
• This changed the design of bridges as they were not limited to such low structural integrity and much sturdier, powerful and larger bridges began to be constructed after this discovery.

Failures of Bridges

Infrastructure Issues

• Infrastructure issues in bridges is a large issue in bridges around the world as this refers to bridges that are aging and need to be repaired, monitored, and maintained as they have become structurally deficient.
• In 2013, the I-5 Skagit River Bridge collapsed due to infrastructure issues as an oversized load crossed the bridge causing it to collapse, this resulted in weight restrictions being placed on the bridge as it was declared functionally obsolete. 

Floods

• Due to climate change there are many more extreme weather events which includes flooding, thus bridges nowadays need to be designed to withstand the pressure from water and other objects that may be picked up by rivers such as trees, building, and other debris. This pressure cause bridges foundations to wash away and break apart it's structural elements.
• Bridges designed years ago did not take into these weather events so most bridges do not have adequate drainage systems or strong enough structures to withstand these forces.
• In 2016, an extreme rain storm in Louisiana damaged the Walsh Road and Stein Road bridges which required them to be replaced. This economic impact could have been avoided by installing drainage systems or adding bridge reinforcements.

Unexpected Events

• Engineers don't know what exactly the future has in store for us and many bridges have had incidents happen due to unanticipated structural or design issues.
• With computer modelling engineers are able to test bridges for unexpected and extraordinary conditions to see how they will hold up during these unexpected events.
• The Tsing Ma bridge which is one of the largest suspension bridges in the world which experiences earthquakes, extreme winds, rough waters, and typhoons was developed using this computer modelling strategy and significantly improved the design of the bridge and others which are still standing today, even after all of these extreme weather events.

Accidents

• Sometimes accidents occur, such as a truck hitting a support post, a train falling off the tracks, or a boat colliding with the foundation.
• Engineers must plan for these types of scenarios to prevent bridge collapses to the best of their ability.
• In 1982, a plane took off from the Washington National Airport and crashed into the 14th Street Bridge. The cars that were struck by the plane dove into the freezing water below. However, only a few hundred feet of the guardrail and wall from the side of the bridge were torn away. This shows how strong and durable the structure was built.

Construction Incidents

• Sometimes there are accidents during construction that result in the collapse of the bridge before it's fully complete.
• This requires designers and engineers to plan the bridge construction step by step to prevent any incidents from occurring.
• In 1907, a bridge in Quebec City collapsed during construction after designers were told that the bridge weight eight million pounds more than estimated at the point in the construction process.
• These designers didn't believe that this was a significant issue and construction continued as usual. The engineer onsite noticed that the frame of the bridge was starting to bend. The engineer made others aware of this however, he was not taken seriously as they claimed the beams were bent when delivered. Soon after the bridge collapsed, killing 75 workers. This collapse was due to the beams not being able to handle the extra eight million pound load.
• This bridge collapse is the reason why engineering graduates wear rings, to remind them of this bridge collapse and our duty as engineers.

Design Flaws and Manufacturing issues

• While these are much less common nowadays, some bridges collapse not long after completion due to design errors or issues with the materials.
• This is why multiple inspections throughout the construction process is necessary to reduce this issue.
• In 1940, the Tacoma Narrows Bridge collapsed four months after completion. A design flaw caused the bridge to shake violently in the wind. Once the bridge reached the same frequency as the wind the bridge collapsed.

Fires

• Although there aren't as many wood bridges as there used to be, fires can still lead to bridge collapses if a tanker truck explodes on a bridge casing extremely hot fires which can melt steel and other structural components.
• Designers have already adapted to this issue by protecting any utility lines that span across bridges so the gas, electrical, or other utility lines don't cause fires.
• In 2016, the Liberty Bridge was damaged in a construction-related fire. The fire started from a welding tool igniting a plastic pipe and tarp. The fire was so hot that it bent a 30-foot steel beam by six inches.
• Bracing and heat treatments were required to bring the bridge back to it's designed structural alignment.

Earthquakes

• Earthquakes are a powerful natural events that occur rarely, however engineers need to design bridges to withstand earthquakes by making them more flexible and rigid in the right places to be able to withstand these powerful events.
• In 1989, the San Francisco - Oakland Bay Bridge collapsed during an earthquake that resulted in significant improvements to the bridge after the collapse. These improvements included replacing existing rivets with stronger heat-treated ones and adding diagonal box beams to provide greater stability when the bridge sways side to side.

References 

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