Steel in the News
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Posted by Tom Klemens on July 8, 2011 at 4:52 PM.
Pedestrian bridge with castellated steel beams, Cappadocia, Turkey. (Click for a different view.) Photos: Martin Anderson.
Martin Anderson, an information specialist in the AISC Steel Solutions Center, sent us two photos of this interesting pedestrian bridge from his recent trip to Turkey.
“The Ihlara Valley is a 10-mile long gorge that cuts through part of central Turkey, in Cappadocia,” Anderson wrote. “Famous for the ancient dwellings and churches cut into the sides of the rock, the valley is a popular scenic attraction with hikers. As part of development plans, bridges have been placed over the stream running through the valley, and we’re pleased to note that one of the footbridges uses castellated steel beams with a wooden wearing surface and rails for a lightweight solution that doesn’t intrude on the surroundings.”
One thing to note is the use of small plates inserted between the two halves of the castellated beam. We asked Brian Ward of CMC Steel Products to shed some light on the extension. “By putting the extension plates in they have increased the moment of inertia about the horizontal axis,” Ward said, “and that’s real benefit of the product.” Moving more of the material further away from the neutral axis means a greater resistance to bending, all other things being equal. And depending on the thickness of the material, Ward said you can spread the pieces a bit and still not make it a slender shape.
Why not just go to a deeper beam? One reason might be the concern over total weight. “To go from the lightest W21 to the lightest W24, for example, means going from 44 pounds per foot to 55 pounds per foot,” Ward said. “But adding by a 3-inch extension plate you can get the extra depth with a nominal increase in weight per foot.” He also notes that in his experience use of octagonal openings is rare for castellated beams.