column and beam deflection laser detector

[howarts]

Hi, is there a device where you can aim it at a column or beam and it can show how much it is in deflection? I can imagine it 2 laser beam hitting the upper/lower or left/right of the member and it can measure micro difference in the distance, hence the deflection. There must be such device. If none.. why none. Geodetic engineers have such devices to measure the lots and physicists have laser that can measure individual molecules. Thank you.

 

[Lomarandil]

Sure.. lots of ways to do it, LIDAR being probably the most robust.

 

[drawoh]

howarts,

Can you load and unload your structure? Will this be a significant cause of deflections?

Lidar may not be accurate enough to show deflections due to load. If you have an element in your structure that rotates due to load, you could mount a mirror to it. If you aim a laser at it from some distance, the reflected beam will magnify any structural rotation. I don't see linear displacement being magnified.

--
JHG

 

[dik]

Can you attach a scale to it and use a theodolite? Also, for small deflections, it may be possible to rig up an LVDT measuring device.

Dik

 

[Lomarandil]

drawoh, we used to use LIDAR with enough accuracy to determine cable tension (when also given a the weather conditions) in transmission lines. So I suspect the accuracy is adequate.

 

[IRstuff]

Aircraft manufacturers have been using instruments for measuring deviations from lines and curves for decades. The question is how much you want to spend. $200k is small potatoes for measuring $200M aircraft structures, particularly if the quantity is large, i.e., 100s of aircraft.

A theodolite and mirrors with bases that can attach to the beam could be envisioned. Assuming a 10 as deflection at 5 ft, that's a 74 micron deflection. Assuming you already have a theodolite for other things, the mirrors and mounts could be had for a few thousand or less, depending on your druthers and accuracy requirements.

TTFN (ta ta for now)
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[SwinnyGG]

we used to use LIDAR with enough accuracy to determine cable tension (when also given a the weather conditions) in transmission lines. So I suspect the accuracy is adequate.

The problem with comparing that to what he's talking about is that for cable tension, the unloaded condition (no gravity) has a known and well defined shape (a straight line) which is linked to the real world shape by a relatively simple equation. The column situation is not that way.

A building column is not a perfectly flat or straight object, and the displacements due to load are likely to be within the same order of magnitude as the inherent deviations from ideal (perfectly flat/straight )are. In order to measure deflection due to load you need a) to know the exact, precise shapes of every member for which measurement is desired after installation but before loading or B) to be able to completely load and unload the building. If you don't have one or both of those, it will be impossible to separate load-induced deflections from the deviations from ideal which are just part of the manufacturing process.