Why steel, not concrete for Highway 305 culverts?

The in basket: Don Hein is puzzled by the material in the new culverts being put under Highway 305 in North Kitsap to remove fish barriers. “I’d like to know why the culverts are made of steel instead of concrete,” he said. “Steel rusts.

“Also, the culverts seem to be made of 1-inch thick steel plate.  How, where and by whom is such thick steel plate rolled into a cylinder?

“You can see one of the culverts close up in the parking lot of the George fireworks stand on Highway 305,” he said.

The out basket: Jerry Moore, state project engineer says, it results from having to pound the culverts beneath the highway.

“Steel pipe was chosen because it can be driven or pushed through the fill at a reasonable cost. Technically, concrete pipe can be pushed through the fill.  However, according to technical reports that I read, special attention has to be given to prevent damage to the ‘brittle’ concrete especially at the joints.  Both the technical reports and our contractor said it would cost more to push concrete pipe through the fill.

“The pipe is made of 1 and 1/8-inch-thick steel,” Jerry said. “This thickness was chosen by the contractor to handle the driving forces generated from the hammer.  Structurally, only 5/8-inch thick steel is required for the load generated by the weight of the highway fill.

“And, yes, steel does rust but not that fast.  The pipe should last more than 50 years especially with the extra thickness.  If, by chance, the steel pipe does rust to a point that it becomes structurally deficient, it can be repaired by relining it with another layer of steel or by other methods.”

Jerry didn’t include information on the maker of the culverts, and I didn’t ask again, but there is no shortage of companies dying to tell you about their steel cylinders online. Just Google it.

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