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Bridge Exerciser

Prevent catastrophic bearing failures
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Many bridges are constructed to be fairly rigid. Because bridges may expand and contract with temperature changes, they are usually built so that one support is fixed and all others can move slightly (often on roller bearings). Unfortunately, if a roller bearing seizes up, the bridge may be subject to compression or tension far beyond its normal design parameters.

My idea would be to use roller bearings at all points (including the normal fixed point) but include a motion-control mechanism at one of the points to move it an inch or so every day or so. This would achieve a number of things:

-1- Bearings are most likely to seize up when they sit still for an extended period of time. Even a small amount of occasional motion may prevent this.

-2- Bearings are most likely to have problems if they are frequently resting in the exact same spot. The motion-control mechanism could be programmed to ensure that it did not stop at quite the same spot every day. Even small differences in location may be sufficient to prevent problems (e.g. move 1" one day, 0.9" back the next day, 1" forward, 1.05" back, etc.)

-3- If a bearing does seize up, it will be detected at the next 'motion cycle', which should be within 24 hours. By contrast, using present monitoring methods, a bearing which freezes up during a long cold spell might not get noticed until the temperature starts to warm up; the temperature could warm up enough to cause damage before anything could be done to fix it.

-4- If a bearing does freeze up, the motor-controlled bearing could be moved as necessary to protect against undesired stresses pending repair of the frozen bearing.

-5- If the motorized bearing freezes up, the situation would be no worse than if it was a fixed point in the first place (though it should still be prepared as soon as practical, lest another bearing freeze as well).

supercat, Aug 11 2007

Bridge bearing http://irpec.lgm.gov.my/prd_bridge.html
Steel/rubber/steel [ldischler, Aug 11 2007]

[link]






       I think bridge failures are far more often caused by corrosion (which turns into stress cracking) than bearing seizure.
nuclear hobo, Aug 11 2007
  

       //if a roller bearing seizes up, the bridge may be subject to compression or tension far beyond its normal design parameters.//   

       This is one of the key points in your argument. Can you cite a couple of your sources for this, or is it just a guess?
MaxwellBuchanan, Aug 11 2007
  

       If our bridges exercised regularly, they would become stronger.
normzone, Aug 12 2007
  

       Parts of bridges do indeed carry huge stresses, but when things are working properly those stresses will be largely balanced out. Even with good bearings, it will certainly take significant force to move a bridge, but if it doesn't have to move very far there should be no particular problem providing it.
supercat, Aug 24 2007
  

       Bridge chiropractors could regularly de-stress the bridge.
normzone, Aug 24 2007
  

       Maybe the bridge would be less stressed if it found a nice tunnel to marry and settle down with.
Galbinus_Caeli, Aug 24 2007
  

       Hm. I don't know, [G_C]. About seven years into it, it would be looking pretty hard at other tunnels.   

       You know, the tunnel starts into the nagging, whining about how the bridge never takes it anywhere, blah blah. And not to mention how the tunnel starts to sag... I'm just saying...
globaltourniquet, Aug 24 2007
  
      
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