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To: dr_lew
These are strange looking contraptions. the rollers look like large rolling pins with cogs on the end. They are supposed to accommodate the thermal expansion of the bridge as a whole.

From my understanding, common practice is to build bridges with a fixed support point, and with movable bearings at other support points. Would it be practical to replace the fixed point with another movable bearing that was attached to a motor that would move it every day or so? I would think that would help prevent the other bearings from seizing up, detect if one of them sizes up anyway (assuming instrumentation at the motor point), and provide an alternate relief point until such time as the seized bearing is repaired. I'd think that would be an all-around win.

36 posted on 08/09/2007 8:09:14 PM PDT by supercat (Sony delenda est.)
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To: supercat
Yes, this bridge did have fixed bearings at one end. I would think that the roller bearings would require some kind of maintenance, such as heavy grease once a year maybe. The report notes however:

At pier 6, there was significant surface corrosion, debris and dirt packed into various areas of the bearing. All the roller bearings seem to have thick coatings of paint and did not appear to functioning as intended under the live load.

"Thick coatings of paint" dear friends! Remember those ads for Caterpillar in Sci Am ? - "The Ideal ... and the Reality."

40 posted on 08/09/2007 8:22:19 PM PDT by dr_lew
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To: supercat

I don’t think you would want to bother using simple-support rollers on both ends. They all have to be restricted in both horizontal directions or else the truss will simply fall off its supports. It’s common practice because it works.

I don’t see how a “sudden quick movement” would necessarily cause a catastrophic failure. I’d be more concerned that the debris held the roller supports in place to act almost like a 2nd fixed joint, building up stress within the structure and possibly being the breaking point for those weak points in the structure.

As someone (some structural person, I think) said on a TV broadcast, it’s probably several factors that melded together that caused this, anyway.


55 posted on 08/10/2007 6:49:15 AM PDT by the OlLine Rebel (Common sense is an uncommon virtue.)
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