Jan. 3, 2017

Our aging bridges face some unexpected modern challenges  

Suspend your fears

More than 26 million people cross the Chesapeake Bay Bridge in Maryland every year, and for most the scenic 4-mile bridge offers breathtaking views.

But for those with gephyrophobia—a fear of bridges—it’s one of the most terrifying places on the planet.

Drivers on the double-span bridge face curves, inclines and declines, a suspension span, and a tunnel-like cantilever span. It’s difficult to see land. The bridge is very narrow, lacks shoulders and see-through railings  allow drivers to peer at the enormous drop of more than 180 ft. In bad weather, visibility can be near zero and the bridge shakes.

It’s no surprise that Travel and Leisure magazine rated the Bay Bridge as the ninth scariest bridge in the world.

For many drivers, the bridge is an unavoidable part of their daily commute, but for those who just can’t deal with it anymore, a unique solution is available.

For $35, nervous motorists can get a driver from Kent Island Express to chauffeur them across the bridge in their own car. Chauffeurs are taught to talk about sports, movies, puppies—anything but the bridge.

Most customers are still nervous and talk non-stop. Some, though, are not soothed at all.

It’s not unusual for people to sit on the floor in the back seat. Others huddle under blankets, and many plug their ears. One woman rode with her head in the driver’s lap, face beside the steering wheel, while her puzzled kids looked on from the back seat.

But even though it’s been requested, no one is allowed to ride in the trunk.

Bad vibes

You may remember back in 8th grade science class that structures like bridges vibrate at a certain natural frequency. An external force with a similar frequency can amplify this vibration and, in rare cases, cause the structure to shake apart and collapse.

Engineers (the ones who paid attention in 8th grade) know all about this phenomenon and have developed ways to protect our modern bridges from stressors like wind and traffic.

However, researchers are now discovering that natural structures are susceptible to these same issues.

The Rainbow Bridge in Utah is a sandstone arch known to be the world’s highest natural bridge. But despite its remote location, researchers at the University of Utah recently found that the arch is picking up all kinds of distant frequencies. It’s so sensitive, in fact, that vibrations from oil-production drilling on the faraway Kansas-Oklahoma border are not only felt by the arch, but their frequency is close enough to the arch’s own to potentially weaken it over time.

Even though these geological formations don’t have a team of engineers to protect them, they do have an amazing ability to adjust their own natural frequency by shedding pieces of themselves. If they’re lucky, these frequency tweaks may reduce the effects of external forces.

Researchers are interested to learn more about the unexpected effects of human activity on structures. Next on their agenda: A study of the effects that shrieking, trembling and wailing have on the Bay Bridge.

Battle to the death

Unlike its natural cousins, the Broadway Bridge in Little Rock, Ark., doesn’t seem to respond to external vibrations—or even dynamite.

Deemed structurally deficient by the state, the 93-year-old bridge was scheduled for demolition this past fall.

The plan was to sever the steel arches and deck with powerful detonations and cause a controlled collapse. Spectators gathered to witness the demolition, but when the explosives went off, all they saw was pigeons flying away. The bridge was still standing.

Even though the initial blast failed, it was no longer safe for workers to place additional explosives. Instead, barges and tugboats used cables to pull on the steel arches, and after five hours they finally came down.

Next it was time for the bridge’s concrete arches to come down. Once again, crowds gathered and explosives were set off, but when the dust cleared, only two of the three arches had fallen. The last arch finally dropped after six hours of hammering with a pneumatic ram.

The last step was destroying a concrete footing, but once again the “structurally deficient” bridge wouldn’t go down without a fight. After 3,500 lb of explosives failed to fully obliterate it, an excavator was brought in to bring this epic three-round battle to an end.

With Little Rock’s new reputation for sturdy bridge-building, local realtors are now fielding a large number of calls from Maryland area codes.

About The Author: Matthews has been chronicling the unexpectedly humorous side of transportation news since 2000. The stories are all true.