Edit post

Edit your reply below.

Post Body
Enter your post below.
[quote user="Falcon48"] [quote user="Bucyrus"] [quote user="blownout cylinder"] [quote user="Bucyrus"] On that same line, there is a much larger, multiple span deck girder bridge on stone piers spanning the Minnesota River at Carver, MN.  In earlier times, the M&StL routinely had commercial divers enter the river and inspect the bedding of the stone piers.  Over the last 20 years or so, one of those stone piers has settled unevenly, apparently due to the river scouring out the bedding for the pier.    Before operations ended, that pier was tipped toward downstream so that its top was about 12”-18” out of alignment.  It was very visible as a large dip and offset in the bridge deck, and in just looking at the pier compared to the rest of the piers.  I found it hard to believe that U.P. continued to use the bridge when the pier bedding was so obviously compromised.  How could you be sure of the pier performance at any given train event when the condition of the pier was obviously changing over time?  How many degrees can you tip a GP-38 before you concentrate so much extra loading on the tipped pier that it tips further?    [/quote] What I'd like to know is how often trains were put through in a day and how fast they would run. I know there would have been restrictions but---- Also what would that offset do to the piers next to the tipped pier----I'd love to have seen what kinds of side loading would have occured with, say, 15 cars loaded---- [/quote] Here is a link showing the bridge at Carver, MN over the Minnesota River:  <A href="http://www.johnweeks.com/bridges/pages/rm01.html">http://www.johnweeks.com/bridges/pages/rm01.html</A>  In the first photo, you can see the misalignment toward the far end.  In the bottom photo, you can see the defective pier, which is third from the left.  In this photo, the river flows toward the camera, and you can see the pier tipped toward the camera as well.  My impression is that the misalignment progressed significantly further than shown here.  During the final operations over the defect, trains were minimal in size, speed, and frequency.  They would consist of one engine (GP-38) and 1-6 cars.  Speed was very restricted over the bridge, to perhaps 10mph or less.  The defect appears to involve only one of the piers.  There is no indication of a structural problem with the integrity of the stone pier itself.  Instead, it appears to be a case of the whole pier being tipped 5-10 degrees due to a loss of footing in the riverbed.    Trees float down the river and lodge against the bridge piers.  Over the last 20 years of operation, the U.P. and previous owner C&NW allowed the trees to accumulate into a huge floating mass covering maybe an acre or more.  Then the company would stage a rail crane and grapple on the bridge to pick the trees out of the mass, and place them on the downstream side of the bridge.  When these tree massing events reached their maximum, they apparently restricted the river to a narrower flow, which accelerated the bottom scouring around the affected pier.   I know that yard tracks can become shockingly misaligned and still pass trains without derailment.  But I found it rather surprising that the company would accept running trains over this bridge defect when is was obviously in the process (although a slow process) of developing abrupt, catastrophic failure.  Moreover, the consequences of reaching that failure point while riding over it in an engine would be quite dreadful for the crew.  Ironically, though, the eventuality of a pending catastrophic failure of this bridge was precluded by the abrupt, catastrophic failure of a small trestle only about mile south, which ended operation over this line.  [/quote] My understanding is that this bridge was inspected much more frequently than other bridges because of its condition.  The continuing deterioration of the bridge would have ultimately led to abandonment of the line, since there wasn't enough traffic to justify a rebuilding once the bridge became unsafe.  But the failure of the trestle you mention hastened the end. [/quote] I would suspect that they would have been really keeping an eye on that Carver bridge as it deteriorated, although I don’t have any specific information about their observations and conclusions.   <?xml:namespace prefix = o ns = "urn:schemas-microsoft-com:office:office" /><o:p></o:p> But just considering the nature of the defect that was developing, I find it hard to imagine how one could establish a threshold where a certain amount of the defect was okay to run on, and once the defect grew beyond that threshold, it would not be okay to run on.  It would seem that to establish that threshold, one would have to assume that the defect was growing at an even rate.  However, I suspect that such a tip-over event would be growing at an accelerating rate.  And learning the exact rate of acceleration would be practically impossible. <o:p></o:p> Bridges can collapse with no visible indication of a problem, so I am amazed that such an obvious, serious, and fundamental problem as a loss of footing that is tipping a pier would not condemn the bridge until it was repaired. <o:p></o:p> In a way, it is rather prophetic that the risky operation over that deteriorating Carver bridge was finally ended permanently by the catastrophic collapse of another bridge on the same line less than a mile away.    The irony is that they had a defective bridge on which they were relying on their own expert assessment of the growing danger to continue operation.  And yet that same expertise on which they were relying for the Carver bridge completely failed them on a bridge less than a mile away.  In retrospect, I wonder what would have happened had not that other bridge failed, and they kept assuring themselves that it was okay to continue operation over that Carver bridge.
Tags (Optional)
Tags are keywords that get attached to your post. They are used to categorize your submission and make it easier to search for. To add tags to your post type a tag into the box below and click the "Add Tag" button.
Add Tag