I.B. Perrine Bridge

I.B. Perrine Bridge

Location: Spans the Snake River at Twin Falls.

History: The bridge is named for Twin Falls pioneer I.B. Perrine, who is known for irrigation and electric power development in Idaho. The original bridge was a cantilevered truss structure spanning 1400 feet, 476 feet above the Snake River. It was built in 1927 and originally operated as a toll bridge. In 1966 bridge inspectors found the bridge was in need of major repairs and maintenance, and questioned whether it was strong enough to carry large truck with heavy loads. In May of 1973, construction was started on a trussed arch bridge beside the original bridge. The second bridge at this location opened in 1976.

Interesting Points: The bridge is one of the few places in the world used for B.A.S.E parachute and bungee jumping: Building, Antennas, Span, Earth.

East of the bridge, is a large dirt ramp that Evil Knevil used for his unsuccessful 1974 attempt to jump the Snake River Canyon on his rocket-powered cycle. Nearly 20,000 people, including 200 reporters, watched the cycle, powered by 5,000 pounds of thrust lift off the ramp at 350 mph. A malfunction caused the drogue chute to open prematurely, while the cycle was still on the ramp. Before the main chute opened, Knevil climbed 1000 feet above the ramp. Then the cycle, with Evel in it, fell to the rocks 470 feet below the rim. Knevil suffered facial cuts, minor bruises and major disparagement.

All work on the bridge was done from the canyon rim because there were no roads in the bottom of the canyon under the bridge.

The old bridge had to be torn down in a reverse process of building , so that no pieces would be dropped into the river below. As the new bridge had been built from both sides at once, meeting in the middle, the old bridge was removed from the middle first, working back toward each side of the canyon rim.

Looking west from the bridge, you see a blue colored, spring-fed lake that supplies much of the drinking water in Twin Falls.

Statistics: The second bridge was built in three years with 4400 tons of steel, 90 tons of bolts, and 5700 cubic yards of concrete. The structure is three bridges in one, with two girder spans at each end and the trussed arch in the middle. It spans 1500 feet, 486 feet above the Snake River. Before construction could begin on the new bridge, the canyon walls had to be secured. Loose rocks and dirt were removed and holes were drilled into the canyon walls to support long anchor bolts, one 30 long, the other 60 long on either side of the canyon. The canyon walls were pressure sprayed with concrete to seal them and keep the rock from falling. Weathering structural steel was used for the framework of the structure. The bridge rusts to a brown color and the rust creates a seal which then protects the steel from the elements.

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