Why Bridges Collapse

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Bridge engineering has been a part of human civilization for many thousands of years. Early bridges were crude structures built out of wood or quarried stone, but the design principles were nonetheless amazing. Building a structurally sound bridge requires considering a lot of different factors from the geology of the area to the integrity of materials, and the estimated amount of traffic and weight placed on the bridge.

Failing to plan for any number of these factors or others can result in a failure of the entire system. Of course, barring extreme miscalculations, most bridge failings result from multiple flaws or events occurring at once. From poor building materials to errors in calculating weight distribution and weather conditions. here are the top 3 reasons, historically, why bridges fail.


Some kind of manufacturing defect in the building materials is a prime cause for bridge failure. From many yards of low grade steel to a single faulty piece that wears and fails over time, materials are a significant cause of bridge failures and are usually accompanied by other external factors. At a more basic level, the positioning and nature of the cement used as a foundational material support is also important in maintaining the integrity of the system. From materials that weren’t designed to support a certain amount of weight in a particular position to poor welding or years of corrosion weakening key structural pieces, material failure is a very real historic cause of bridge failure and continues to be a design flaw to this day of refined engineering practices.


Design and material failures often go hand in hand, however, the bridge design often condemns a bridge to failure before any materials are even placed together. The architectural designs and engineering plans determine everything about the bridge construction, from appearances to weight capacity to weather resistance. Flaws in designing for weight distribution continue to be a major cause of bridge collapse. Structural elements supporting multiple points of weight without the proper reinforcement and poorly fitted pieces are serious concerns in bridge designs. Underestimating loads on particular parts of the bridge and proper supports tying up vulnerable areas are also major issues in bridge design and construction.

Natural Events

This can mean anything from heavy rains causing flooding to fires and earthquakes. Natural disasters are a major cause of bridge failure. Since bridges often suspend and connect to points across bodies of water, floods and hurricanes can be a significant events that compromise the bridge’s integrity. In high risk areas, ‘disaster proofing’ bridges is typically an important factor that is included in the engineering plans, but bridges still fail for no other reason that the intensity of a natural event. Floods bring debris that can weaken and damage structural supports. High winds can weaken already old, vulnerable bridges. Seismic activity is probably the worst thing that can happen to a bridge since the entire geologic foundation of the bridge is compromised.


by Ben Vaughn

Ben Vaughn writes on the reasons bridges fail, environmental risks associated with urban development, and sustainable building practices.

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