10 Causes Behind Bridge Failures

Main Points

You might not give much thought to the bridges you cross on your daily commute, but these structures are far more than just aesthetic elements that ease your travel. Bridges are vital infrastructure that transport vehicles and trains over rivers, valleys, or other roads. A bridge failure or even a temporary closure can lead to severe traffic congestion or even isolate communities, particularly those on islands.

Some of the most monumental and costly engineering feats in history have involved constructing bridges. While the basic principles of bridge-building have been understood for millennia, each bridge brings its own set of unique challenges. These challenges can include the local geology, traffic loads, weather conditions, and the choice of materials. At times, these factors are misjudged, or unforeseen events can occur, leading to tragic outcomes.

As we examine these 10 reasons behind bridge collapses, remember that most failures result from a combination of factors. For instance, a flood damaging bridge supports may not directly cause a collapse, unless there's also a design flaw or poor maintenance. Remove one of those elements, and the bridge might have remained standing. In other cases, a train colliding with a bridge can lead to its sudden failure. We'll explore these scenarios in more detail on the next page.

10: Earthquake

Earthquakes wreak havoc on all types of structures, including bridges. While major earthquakes often cause extensive building collapses, it’s the destruction of bridges that frequently serves as the most visible reminder of the disaster's impact. The image of a collapsed bridge, captured by news helicopters, becomes an indelible symbol of the disaster’s scale.

Such was the case with the Loma Prieta earthquake that struck the coastal cities of Oakland and San Francisco in October 1989. This powerful earthquake, named after a nearby mountain, resulted in 63 fatalities, the majority of which were due to the collapse of two bridges. One person died when a section of the San Francisco-Oakland Bay Bridge fell, while 42 others lost their lives when a large section of the Cypress Street Viaduct on Interstate 880 gave way [source: USGS].

Thankfully, bridge collapses caused by earthquakes are fairly uncommon. Moreover, bridges in earthquake-prone areas can be engineered to endure seismic activity, or at the very least reduce the potential loss of life during an event.

9: Fire

While fire may be one of the rarest causes of bridge collapses, it has historically brought down several bridges, particularly when they were made of wood. Train bridges were particularly vulnerable due to the frequent sparks created by steel train wheels on steel rails. During dry conditions or strong winds, those sparks could ignite the bridge, causing it to burn down completely [source: Letchworth].

Bridge fires aren't merely a relic of the past. In recent years, some modern bridges have collapsed or sustained severe damage due to fires. These fires are often triggered by accidents involving tanker trucks carrying highly flammable substances like gasoline. A crash can result in an explosion and an intense blaze hot enough to melt the steel, weakening the structure until it eventually collapses.

This is exactly what happened in 2009 when a tanker truck on I-75 near Detroit suddenly burst into flames directly under a bridge. The resulting inferno destroyed the bridge completely and forced the closing of I-75. Amazingly, no one was killed [source: Guthrie].

8: Train Crash

This type of bridge collapse is extraordinarily rare, but one of the worst rail disasters in history, the Eschede train disaster, was a bridge collapse caused by train impact. In 1998, a high-speed train traveling through Germany suffered a mechanical malfunction of one of the wheels. The broken wheel struck a switch and shifted it, throwing subsequent cars onto a different track. Moving at roughly 124 miles (200 kilometers) per hour, the cars derailed and slammed into the piers of a road bridge that passed over the railroad tracks at that point. The massive impact brought the bridge down directly onto the passenger cars of the train, crushing them. As a result, 101 people died in the accident [source: Oestern]. Eighty-three people lost their lives in a similar tragedy near Sydney, Australia in 1977 [source: ABC News].

7: Boat Impact

Many bridges span rivers and other bodies of water. While boats typically move slowly under a bridge compared to trains, their immense mass gives them the potential to exert significant force. Even a barge, which moves at a slow pace, can cause considerable damage if it collides with bridge supports or piers. In some cases, this force can be enough to bring the bridge down.

One such incident occurred in 1993, when the Judge William Seeber Bridge in New Orleans collapsed. A barge struck one of the bridge's supporting piers, severing it. This caused nearly 150 feet (46 meters) of the bridge to fall. Tragically, a motorist on the bridge at the time lost their life in the accident [source: NTSB]. Over the past century, more than a dozen major bridge collapses have been caused by boat collisions [source: Wardhana].

6: Flood

Floods contribute to bridge collapses in several ways. Intense flooding can cause rivers and streams to overflow, picking up debris such as trees, cars, and parts of buildings. As the river rushes under the bridge, the high water level pushes the debris into the structure. If the collision doesn't immediately destroy the bridge, the combined weight of the debris and the force of the water can bring it down. A historic example of this was the collapse of the Conemaugh Viaduct in 1889, when the South Fork Dam in Pennsylvania failed and released a devastating wave of water down the Little Conemaugh River [source: NPS].

Flooding can have a devastating impact on bridges, not by simply washing them away, but by slowly eroding the earth surrounding and beneath the bridge piers. This gradual process is referred to by engineers as scour, and it takes place whenever bridge foundations are submerged in water. While the natural flow of water can erode the soil over many years, bridges are typically designed to endure such conditions. Engineers can also use methods like placing riprap, which involves laying heavy rocks to prevent erosion. However, floods can significantly intensify the water’s force and volume, leading to more severe erosion, which might cause the bridge to collapse suddenly or within a few days or months. According to a study by the American Society of Civil Engineers, 53 percent of bridge failures are linked to flood and scour events [source: Wardhana].

The Schoharie Creek Bridge is a prime example of a collapse caused by flood and scour. This bridge spanned the New York State Thruway over Schoharie Creek. During the spring floods of 1987, high water levels eroded the soil beneath one of the bridge’s piers, creating a massive hole nearly 10 feet (3 meters) deep. The weakened pier caused the entire bridge to collapse, resulting in the tragic loss of ten lives [source: Storey & Delatte].

5: Construction Accidents

Bridge collapses during construction are more common than one might expect. While these failures might not seem as critical since no vehicles are on the bridge at the time, they can be just as deadly. Some of the most fatal bridge collapses in history occurred while the bridge was being built. Unlike a completed bridge with only a few vehicles crossing, a construction site hosts hundreds of workers, all of whom are in significant danger if the structure fails.

The collapse of the Quebec Bridge in 1907, which spanned the St. Lawrence River near Quebec City, serves as a stark reminder of the potential consequences of engineering miscalculations. Although the bridge was only partially built, sections of it were already warping and cracking under the weight of its own structure. Engineers voiced concerns but couldn't act fast enough. The bridge ultimately collapsed, resulting in the tragic loss of 74 workers. Remarkably, during its reconstruction in 1916, the bridge collapsed once again, claiming the lives of 13 more workers. It was finally completed in 1917 and still stands today.

4: Manufacturing Defect

Some bridge collapses remain baffling at first, with their true cause only uncovered after extensive investigation. Experts sift through the wreckage, reviewing inspection reports and gathering eyewitness testimonies to unravel the mystery. At times, a seemingly insignificant failure in a small part of the bridge causes a catastrophic collapse. In other cases, the use of substandard or defective materials weakens the bridge, making it unable to withstand the test of time.

The collapse of the Silver Bridge over the Ohio River at Point Pleasant, W. Va., in 1967 is notorious not only for the tragedy but also its ties to Mothman, a strange creature allegedly seen near the area just before the disaster. The true cause, however, was a manufacturing defect in one of the steel eyebars that supported the bridge. Years of corrosion aggravated the flaw until it finally gave way, causing the bridge to collapse and claiming 46 lives [source: LeRose].

In 1994, the Seongsu Bridge in Korea fell due to poor-quality steel used in certain sections and faulty welding techniques during its construction. The tragedy claimed the lives of 32 people [source: Korea National Emergency Management Agency]. Similarly, in 2006, the De la Concorde overpass in Laval, Quebec, collapsed, killing five. The investigation revealed that several construction errors had been made, deviating from the original design, and inferior concrete had been used, which ultimately failed to support the structure.

3: Design Defect

There are instances where a bridge's collapse is essentially unavoidable, as the flaw lies not in its construction but in its original design. From the moment the plans were drafted on paper, the bridge was destined to fail.

One of the deadliest accidents in U.S. history occurred when the walkways in the Kansas City Hyatt Regency Hotel collapsed. These walkways connected the second, third, and fourth floors, spanning above the hotel lobby. On July 17, 1981, the walkway on the fourth floor gave way, falling onto the second-floor walkway directly beneath it. Both walkways then crashed into the lobby below, which was filled with people watching or participating in an evening dance contest. The collapse resulted in 114 fatalities [source: Associated Press].

What caused this disaster? A redesign of the original plan led to the walkways being constructed in such a manner that structural elements were forced to support the weight of both the second and fourth-floor walkways at the same time, effectively doubling the load. Investigations revealed that the initial design was already too weak to bear substantial weight, and the modifications made the situation far worse [source: Martin]. The collapse was almost unavoidable at the most tragic moment.

The collapse of the I-35 Bridge over the Mississippi River in Minneapolis, Minnesota, in 2007 was another tragic instance of a design flaw. The steel gusset plates that connected vital parts of the bridge were insufficiently sized. The added weight from concrete resurfacing and construction equipment caused these plates to bend, leading to the collapse of the entire structure and the loss of 13 lives [source: NTSB].

2: Poor Maintenance

Diagnosing poor maintenance as the cause of a bridge collapse can be difficult. Many collapses that could have been avoided were exacerbated by inadequate inspection and maintenance. Engineers design bridges assuming a minimum level of upkeep that is necessary to ensure the bridge's longevity. This includes replacing rusted components, clearing drainage systems, reapplying protective paint, and reinforcing the structure if traffic volume increases over time.

In June 1983, a bridge on the Connecticut Turnpike, spanning the Mianus River, collapsed in the middle of the night. The collapse was attributed to the failure of steel pins that had corroded. Investigators concluded that the design and construction of the bridge were not at fault; rather, the disaster resulted from deferred maintenance that could have identified and replaced the deteriorated pins [source: NYCRoads].

1: Odd Occurrences

While we've examined many causes of bridge collapses, there are instances where the collapse cannot be attributed to any of the usual suspects. Instead, these failures were the result of occurrences that can only be considered highly unusual.

During the 1958 Cuban Grand Prix, legendary driver Juan Fangio was kidnapped by socialist revolutionaries before the race, but that wasn’t the most shocking part of the event. The racecourse had no guardrails or safety fences; instead, spectators stood directly at the edge of the track. As the race unfolded, driver Armando Garcia Cifuentes lost control of his Ferrari, plowing into the crowd and destroying a temporary pedestrian bridge in the process. This tragic accident resulted in the deaths of seven people [source: Edmondson].

The Lacey V. Murrow Memorial Bridge in Seattle spans Lake Washington. As a floating bridge, it rests on pontoons. In 1990, an odd sequence of construction errors led to water filling the pontoons, which was meant to be used for resurfacing, compounded by rain and lake water from a storm. Over several hours, the bridge sank to the lake's bottom.

The Winkley Bridge, a pedestrian suspension bridge in Arkansas, was infamous for its significant swaying under load. In 1989, a group crossing the bridge began swinging it intentionally. The resulting intense sway caused the bridge’s support structures to fail, leading to a collapse that claimed five lives [source: Bridgehunter].