Why did the bridge in the US collapse so quickly when a freight train hit it?

The 1970s design of the Francis Scott Key Bridge may not have been strong enough to protect it from strong impacts from large container ships.

The moment a freight train crashed into the Francis Scott Key Bridge in Baltimore city, Maryland, USA early on the morning of March 26. (Video: X/HaywerdJablomi)

A giant cargo ship crashed into the Francis Scott Key Bridge in Baltimore, Maryland on March 26, leaving many people missing and greatly affecting the socio-economic situation. There are many questions about the collision, including why the train hit the bridge directly and why the bridge collapsed so quickly as the accident occurred, according to Independent . Experts say it may be too early to tell exactly what happened during the collision and subsequent collapse. However, they emphasized that bridges of this type especially need to be built with such protection against collisions and require huge impact forces to cause the bridge to collapse.

Many bridges have collapsed due to collisions with ships in the past. From 1960 to 2015, there were 35 major bridge collapses that occurred after being hit by ships, according to researcher Toby Mottram at the University of Warwick. That existential risk motivates the construction of modern bridges with anti-collision capabilities. Engineers have developed a series of safety requirements and solutions to ensure bridge stability in the event of a collision.

(Video: AFP).

Large bridges spanning sea routes require measures to protect bridge bases and supports. Protection measures come in many different forms, according to Robert Benaim, a bridge designer and PhD student at the Royal Academy of Engineering. "It can be in the form of structural protection such as inserting steel structures on the seabed to stop or redirect ships. In addition, artificial islands can be used for large ships, so that ships never get close to the foot of the ship. demand ," Benaim said.

The Francis Scott Key Bridge is relatively modern, so experts believe the bridge was built in anticipation of a collision. The foot of the bridge is very important because any structural damage to that part, especially at the center point, can cause the entire bridge to collapse. According to Lee Cunningham, associate professor of structural engineering at the University of Manchester, train mass and speed are the main factors determining the level of impact force. Similarly, the collision direction is also an important factor, calculated based on the position of the moving stream.

In the case of the Francis Scott Key Bridge, its 1970s design may not have taken into account the enormous size and power of the ships running underneath today. The cargo ship that crashed into the bridge named Dali was very large, 300m long and 48.2m wide, carrying a large amount of goods and moving at an unknown speed. According to Professor Mottram, it is conceivable that the foot of the bridge was not designed to withstand the scale of collisions with modern ships, because ships like the Dali did not pass through Baltimore Harbor at that time. Although it met safety standards and design regulations in the 1970s, the Baltimore Key bridge may not be equipped with protection to cope with modern ship movements.

The bridge collapsed and the container ship caused an accident.

However, Professor Mottram also emphasized that it was not just the technology on the bridge that failed to avoid a collision disaster. "The navigation technology could have prevented the train from crashing straight into the foot of the bridge ," he said. According to Mottram, the investigation direction should prioritize clarifying why this technology does not work on the ship.

In the video recording of the collision, what is notable is the speed at which the bridge collapsed. As soon as the bridge began to buckle, it quickly collapsed completely. This is partly because the project is built as a continuous truss bridge, made from long steel trusses running over three main spans, instead of many connected sections on the foot of the bridge.

Collisions with large vessels such as the freighter Dali far exceed the design load for the elongated concrete foot of the bridge, which supports the truss structure. As soon as the foot of the bridge is destroyed, the entire truss structure will collapse extremely quickly , explains Andrew Barr, a PhD student in the Department of Civil and Structural Engineering at the University of Sheffield.

"This is an example of a process that engineers call chain collapse , in which damage to one structural component leads to failure of the adjacent component, resulting in the inability to support new lateral loads. above. In this case, the collapse of the bridge pier causes the unsupported part of the truss above to buckle and fall. Because this is a continuous truss, the load is redistributed. The truss part rotates around the remaining bridge pier. like a seesaw, temporarily raising the north span high before the tension caused it to collapse as well. As a result, the entire truss collapsed into the water ," Barr shared.

The freight train hit the beam of the Francis Scott Key bridge in Baltimore, Maryland, causing the bridge spans to collapse and many vehicles to fall into the river.

Video on social networks shows a large cargo ship crashing into the Francis Scott Key Bridge around 1:30 a.m. on March 26, causing the bridge spans to collapse one after another into the Patapsco River.

At least 20 people and many vehicles fell into the river. The ship also caught fire after the collision.

Officials said the ship that caused the incident was named Dali. According to data from the ship tracking website MarineTraffic, Dali is a Singapore-flagged container ship, moving from the port of Baltimore to Colombo, Sri Lanka.

Francis Scott Key is a steel bridge spanning the Patapsco River, a transportation artery connecting to the Port of Baltimore, serving the needs of transporting goods by water on the East Coast of the United States. The bridge was inaugurated in 1977, has 4 lanes and is 2.5km long, named after the author of the American national anthem.