Spanning the Gap

Bridge Building, Past and Future

Every day, many of us walk, bike, or drive over bridges or skyways without paying a second thought to their importance in connecting us across roads and highways, rivers, lakes, mountains, or from one building to another. From wooden bridges in parks and forests to massive, magnificent structures like the recently-completed Hong Kong–Zhuhai–Macau Bridge, they are vital to our everyday lives.
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The Hong Kong-Zhuhai-Macau Bridge – made at the cost of approximately $20 billion US from 400,000 metric tons of steel – is actually a system of bridges and tunnels spanning thirty-four miles and a remarkable engineering achievement. The bridge is designed to last 120 years and bear the force of earthquakes and other natural disasters.

The bridge was not erected without controversy since at least eighteen workers perished during its nine-year construction, about the same number who died during the building of the world-famous Brooklyn Bridge.

The 1,595-foot Brooklyn Bridge – which spans New York’s East River – was the world’s longest suspension bridge and a marvel of engineering and construction when it opened with great fanfare on May 24, 1883. World records seldom last, however, and the bridge’s length has been dwarfed many times over by other bridges since it was built.

The world’s longest suspension bridge currently is Japan’s Akashi-Kaikyo Bridge, with a record span of 6,532 feet and a total length of 12,831 feet. It joins the list of ten longest suspension bridges in the world with the others located in China, Japan, South Korea, Denmark, the United Kingdom, and Norway.

As remarkable as bridges can be, disasters have occurred with lives tragically lost during the construction process or shockingly soon after completion, much like Washington’s Tacoma Narrows Bridge, which opened to traffic in July of 1940 and fell to pieces during a fierce windstorm just four months later. The suspension bridge had been nicknamed ‘Galloping Gertie’ due to its wild, whipping movements during windstorms.

On March 15, 2018, the world was stunned when a massive, 175-foot section of the $14.2 million FIU-Sweetwater UniversityCity pedestrian bridge collapsed in mere seconds onto the Tamiami Trail, the southernmost section of U.S. Highway 41. Eight vehicles which had the misfortune to be driving beneath the bridge at that moment were crushed, and six people died. The company behind the bridge, Magnum Construction Management LLC, is facing eighteen lawsuits for wrongful death and personal injury for the failure of a bridge that was meant to improve pedestrian safety.

Unlike other failed bridges, the FIU-Sweetwater UniversityCity was not made of steel and wire but concrete. It was built using a technique called accelerated bridge construction (ABC), which enables bridges to be replaced quickly, with the least amount of disruption to the flow of traffic and reduced risks to construction workers and the public. The main section of the 320-foot bridge had been placed on March 10, just five days before it collapsed.

It should have maintained its structural integrity for over a century, but cracks were soon discovered and reported on March 13 by the project’s lead engineer. Further signs of impending problems occurred when, at 9 a.m. on the day of the collapse, a university employee heard a cracking sound. Just hours later, at 1:47 p.m., the defective section came crashing down, horrifically captured on time-lapse video.

The subsequent National Transportation Safety Board (NTSB) investigation into the cause of the collapse revealed numerous red flags. Experts criticized the bridge’s unusual zigzag diagonal support structure, which was uneven, resulting in insufficient support for the strut and anchor to bear the weight of the enormous bridge section.

An article in FIU News entitled First-of-its-kind pedestrian bridge ‘swings’ into place, heralded the placement of the main section of the state-of-the-art bridge as it was lowered into what was supposed to be its permanent spot for decades. “The main span of the FIU-Sweetwater UniversityCity Bridge was installed in a few hours with limited disruption to traffic over this weekend,” the article stated.

“FIU is about building bridges and student safety,” stated FIU President Mark B. Rosenberg in the article. “This project accomplishes our mission beautifully.” The ABC method of bridge construction used to build the doomed bridge was being advanced at FIU’s Accelerated Bridge Construction University Transportation Center (ABC-UTC). Although meant to be able to withstand a Category 5 hurricane, less than a week later, the bridge section, weighing a staggering 950 tons, came crashing to the ground.

The bridge was the first in the world to be made entirely of self-cleaning concrete, incorporating titanium dust to remove pollutants and keep its surface a shimmering white, and was America’s largest pedestrian bridge moved via self-propelled modular transportation (SPMT). Sadly, these innovations and others, including environmentally-friendly LED lighting, did nothing for the structure.

Given the extreme safety and engineering considerations in their design, bridge disasters are usually associated with natural events or aged and weakened structures, not bridges built just days or months earlier. One of the most recent bridge collapses was not totally unexpected. The pedestrian bridge was constructed in 1939 and was once part of a Packard assembly plant in Detroit. This old, unmaintained bridge had been off limits to the public for years before it fell.

However, even more recently constructed bridges, such as the Morandi Bridge in Genoa, Italy, are not immune to disaster if not properly cared for. Witnesses said that the bridge was struck by lightning before it fell, but engineering.com stated this would not be enough to fell the fifty-one-year-old bridge, adding “Preliminary investigation points to a combination of poor design, questionable building practices, and insufficient maintenance.”

The 3,878-foot cable-stayed bridge with a reinforced concrete deck tumbled to pieces on August 14, 2018, killing forty-three people and leaving another six hundred homeless. For Italy, a nation priding itself on centuries of concrete-making extending back to ancient Rome, the Morandi Bridge failure came as a huge blow.

In the very near future, expect drones to play an increasing role in bridge building and inspection. As infrastructure costs become greater – making future replacement costlier – and newer materials are introduced, bridges will need to be engineered to last much longer than ever before, with self-cleaning coatings and low-energy lighting to reduce maintenance and operating costs.

Land is becoming scarcer in large cities worldwide, so bridges of the future will serve multiple purposes. Where they were previously used only to move people and vehicles, more bridges may serve as public gathering places in the coming years. Washington D.C.’s 11th Street Bridge Park, planned to open this year, calls for a bridge, enclosed café, and environmental center, all within a large central plaza.

Many bridges are iconic, like San Francisco’s famous Golden Gate Bridge which is still the most photographed bridge in the world over eighty years after it was unveiled. But bridges, walkways, and overpasses do not necessarily have to be massive to be remarkable. The Grand Canyon Skywalk opened in 2007. This is a horseshoe-shaped bridge supported over the world-famous canyon with an elevation of 4,770 feet. It provides breathtaking views of the Grand Canyon, one of the natural wonders of the world.

Not to be outdone, China – already home to many of the longest bridges on earth – is also where many of the most terrifying are to be found. Hebei Province is the location of the 1,601-feet glass sky bridge at Hongyagu Scenic Area in Shijiazhuang. China also has the Tianmeng Mountain Pedestrian Bridge in Linyi, Shandong. Its 1,378-foot length makes it the longest spanning pedestrian bridge in the world.

These are more than tourist attractions for thrill-seekers who want to walk on glass thousands of feet in the air. These bridges and others boldly push the boundaries of what is possible and represent the future of construction.

While glass-bottom bridges appeal to thrill-seekers and the curious, they are also marvels of design and engineering and leave us wondering how they were built and what the future of bridge-building around the world might be.