Makes Sense To Me
Margie Kieper has been filling in at Dr. Jeff Masters for several days. At the end of today’s post she notes that she can see the site of the bridge collapse from her office window and then presents a possible scenario for what happened that involves a week of high temperatures, vibrations, and the method used to construct the bridge.
Her theory rings true to me because in the early pictures of the collapsed sections the bridge support that failed was showing under the roadbed sections. From what I saw I assumed the supports were a metal frame work, like a lot of railway bridges. But then later images showed what appeared to be concrete supports that were still standing. It was as if the support that failed had lost its concrete outer coat, before it collapsed.
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Regarding the different expansion coefficients of steel and concrete… any maker of woodwind instruments who has bothered to look at which 19th- and early 20th-century instruments survived and which did not, will understand immediately why encasing a metal interior in an exterior of another material has significant risks.
For a while, before I gave it back to its original owner (whose grandfather had owned it), I had a flute, made probably in the 1860s, the head joint of which was some black hardwood lined with a sleeve of some metal. I’m sure it had desirable playing characteristics in its day, but its structural collapse… cracks in the wood of the headjoint… was inevitable from the very way in which it was made. Woodwind instruments regularly encounter extreme “weather” … drastic short-term temperature and humidity changes… in their normal daily use. The catastrophic failure of a lined headjoint can, I’m told, be quite loud, almost like a gunshot.
These days, wind instruments are typically made of wood or of metal, but not of both (at least not in the same segment of the instrument). Bridge designers, please take note.
It’s a common method used in engine work to remove “frozen” bolts to use fire and ice to expand and contract components to free them up.
At the college I worked at in New York they had a heated ramp – copper pipe laid in the concrete through which warm water flowed in the winter to prevent ice. The concrete would flake off that area with great regularity.