Holy smokes! We've all seen flimsy rope bridges collapsing in movies, but how about a heavy-duty steel road bridge? Just check out this slow-mo video of the largest bridge ever demolished in Texas, shot at 300 frames per second by Austin onlookers Kirk Drummond and Mike Mitra.
So how did the demolition experts make this happen? "The key to any bridge demolition is research, planning and coordination," explained Greg Malatek, TxDOT Austin District Engineer.
To demolish a bridge, the demolition team first has to know how it’s put together. This 70-year-old bridge in Marble Falls, TX is a cantilever truss bridge, which means it’s made up of arms supported on one side that project toward the middle and hold up an otherwise unsupported central span.
How did this implosion happen with such precision? “We used linear shaped charges [explosives that are configured to slice through material in a straight line]. This allowed us to concentrate the blast in the proper area to cut the steel,” said Malatek.
These charges, placed at regular intervals throughout the structure, are activated by the detonating cord that you see light up along the bottom of the bridge. This sequence demolishes the bridge in a controlled way that minimizes impact on the surrounding area.
The electric charges leaping from left to right under the bridge sure look cool, but they also serve a practical purpose. Malatek explains, “The delay helps to offset the total volume (decibel level) of the blast, causing the noise to be somewhat reduced.”
Due to the impact of an implosion like this one the on surrounding area, very few bridge projects require the use of explosives. Many bridges are taken down mechanically by pulling pieces apart using specialized machines. Malatek says that he and his team have only performed a handful of explosive demolitions.