Stories of bridges and incredible load tests

From the Brăila bridge to the Brooklyn Bridge, those incredible stress tests for infrastructures

The Brooklyn Bridge was opened to the public on May 24, 1883, and immediately became a symbol of New York and a tourist attraction. However, it took a whole year before New Yorkers fully embraced the suspended bridge, which was the longest in the world at the time. The leap over the East River was so imposing and unusual that many were afraid to cross the central span. Stability and solidity were major concerns regarding the infrastructure supported by steel cables.

Seven years before its inauguration, during the cable installation, the chief mechanical engineer, Edmund Fisher “EF” Farrington, even became a tightrope walker to demonstrate the strength of the towers and steel cables. After anchoring a metal rope to the two towers, he launched himself into the void, sitting on a board tied to the rope, holding his hat with one hand and the rope with the other. EF completed the crossing of the bridge in 22 minutes, but his gesture did not convince the city, which had to wait until May 17, 1884, one year after the opening, to trust the bridge.

To convince them, Phineas Taylor “PT” Barnum, the founder of Barnum’s circus, came up with a marketing idea. He had already offered to stage a parade for the bridge’s inauguration ceremony but was rejected. The growing fear among the citizens on both sides of the river was such that few dared to set foot on the structure. The mayor decided to call Barnum, who eagerly accepted. The march from one shore to the other involved 21 elephants, escorted by Jumbo, the most famous and majestic of the group, along with 10 camels, seven dromedaries, and other exotic animals. This instantly dispelled all doubts.

Bridge load testing: the Golden Gate bridge

After that impromptu and triumphant static and dynamic load test, suspension bridges became a new frontier for experimentation, not only in the United States. Resistance testing gradually became a vital element for the success and structural completion of a project. In February 1932, in Australia, 96 steam locomotives were made to pass one after the other on the two roadways of the famous Sydney Harbour Bridge, an arch steel bridge with a suspended roadway.

Over the years, testing techniques have advanced in parallel with the progress of engineering, climate conditions, and the morphology of the two bridge banks. The Golden Gate Bridge in San Francisco, opened in 1937, required high resistance to wind, strong currents from the underlying Pacific Ocean, and the potential for earthquakes due to the feared San Andreas Fault. The construction served as a model for other suspension bridges, and over its 90-year lifespan, it has seen numerous improvements. On its 50th anniversary, May 24, 1987, the bridge was closed to traffic to allow people to walk across it. Approximately one million people responded to the invitation, creating an overwhelming crowd under which the central span experienced a temporary deflection of 7 feet (slightly over 2 meters), leaving the residents of San Francisco with the idea of an invincible bridge.

Technologies and innovation in bridge testing

In the modern era, with the help of advanced technologies, static and dynamic load tests, wind tests, and resilience to atmospheric or seismic phenomena are carried out using sophisticated control and simulation systems. Testing begins with the initial design, including laboratory analysis and the origin of the materials used. The most visually dramatic (though no less technological) aspect involves the transit of a massive number of trucks placed at precise locations, measuring the structure’s responses to vibrations, speed, weight, and all other components that could influence the central span, banks, and cables.

Brăila Bridge load test: 60 trucks like 400 elephants

Last June, the testing of the Brăila Bridge in Romania, constructed by Webuild, was completed. For several days, up to 60 trucks with a total weight of 2,400 tonnes were positioned on the deck of the suspended bridge over the Danube River, which will be the second longest in Continental Europe. To make a comparison with the Brooklyn Bridge, this weight corresponds to the passage of approximately 400 elephants. Two of these trucks traveled the entire bridge at a speed of 80 kilometers per hour to test its vibrations.

Other iconic crossing structures in Webuild’s portfolio, such as the new San Giorgio Bridge in Genoa, Italy, the Long Beach International Gateway in California, the Third Bosporus Bridge in Turkey, and dozens of others, have undergone extensive testing with the passage of heavy vehicles. From Barnum’s elephants to locomotives, trucks, and even the Batmobile, which raced at high speeds on the Yavuz Sultan Selim Bridge (the third Bosporus Bridge) during the filming of a Batman series movie, designed to withstand winds up to 300 kilometers per hour.