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EDITOR:
I read with interest the front page article on June 11 about the Pony Express Trail. When I got to Page 9, there was a picture of an artist’s conception of a bridge to connect the trail over the river. It looks great but it is a wonder that the bridge didn’t collapse, before the picture was finished. It would fall of it’s own weight much less with people and horses on it. I am not a Civil Engineer but there is no way that the pictured bridge would work as the physics wouldn’t allow it. As an arch bridge, the arch is too shallow to let compression of the materials hold it up. It isn’t a cantilevered bridge as the materials aren’t husky enough at each end to sustain the leverage produced by the span. It isn’t a catenary ribbon because the arch is up not down. There is a whole lot of bridge engineering missing.
I don’t know what type of bridges were in place in the past but they certainly weren’t as shown in the picture. Also, the river, while placid as shown, isn’t friendly to any supports that would be necessary to hold this bridge up, when in full flood mode. I doubt that any bridge could be built today at that location for $3 million alone, much less the approaches and interpretive center. I would bet that the permitting process and engineering costs would eat up a good portion of the bugeted amount before the construction and materials costs were calculated. There is a valid reason that the former bridges were not replaced, mainly the cost/benefit ratio. The pictured bridge is pretty but not possible, both physically and financially.
BYRON MOBUS
Cameron Park
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J. OthersideJune 18, 2012 - 7:31 pm
Byron, try evaluating assuming the railings are structural boxes and the running cables are under tension to pre-stress the arch. Can't say much about the financials, have never seen an engineering cost come in less than twice the preliminary estimate. So $6 million would be my best guess.