Just prior to the I-5 bridge collapse Thursday night north of Seattle, eyewitnesses report an oversized load struck a portion of the bridge’s steel superstructure. That’s the frame that’s key to holding the bridge up.
The I-5 bridge over the Skagit River was built in 1955. It’s a truss style structure. Bridge engineer Stanley Ryter says all that steel above.
"Think of it as a 16 ft tall beam and if any part of that breaks then you lose the ability to carry the load," Ryter says.