Measuring the Verticality of a Column Using Piano Wire

The question is, did the photographer employ the Scheimpflug principle in taking the photograph? (Monorail camera)

Who knows, but you could just make a much longer line and move the plumb right up next to the actual building, which was what I was actually hinting at.

Scheimpflug is used to perfect focus of the intersecting planes.

Controlling the perspective would determine the vertical linearity, or plumb.

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I think the OP needs a carpenter.

Upto 60meters how can we use plumb line is it not difficult?and wind forces will act on the line which makes the line to deviate is not correct?

Yes, laser plump is the best solution. Laser plump comes very helpful and handy for vertical column erections/inspections, very popular are wind mill towers.

plump ≠ plumb

--Ed. C.

Got it, I'm sorry...

Then you have to align the laser beam to the center of gravity.

No. Most are self leveling.

It's simple to use, not affected by wind, and very accurate.

Here is one by Pacific Laser for $200. I have seen other self leveling ones by Stanley for $50 and up.

Lasers can be off as much as .250 of inch or more per 100 foot. Need to look very carefully at the manufactures specification for the unit you wish to use. Laser level not that accurate, just easy to use.

You mostly get what you pay for.

Usually, renting pro equipment is a good choice.

And if you don't know how to use it, contracting a professional is an excellent idea.

This works:

Can you make sure you have build in one line for 60 m?

What tolerance do you apply to your measurement? 1 mm? Well then:

If you use a 3 m wire the error you might get is 20 times more at the top of your column. If you can tolerate 20 mm possible deviation at the top of the column 3 m is ok.

If not use 6 m wire length. This will reduce the error to 10 mm.

As for the wind having an impact on the wire you need to hang a heavy weight from the wire to straighten it out. Dont measure at high wind!

Using laser eqipment might get the deviation down a fair bit.

What accuracy do you want. You stipulate using piano wire but then say, correctly, that the wind will move it.

There are other ways. Using a theodolite, measure a distance from the column at ground level and from there, measure the angle to the top of the column, move a further measured distance in the same line and take another angle to the top. From those readings you can calculate the distance out of vertical.

Get a transit, flag poles and a reading glass.

Measure two known distances from the base of the column. Measure the height of the column (if you don't already know it, it can be calculated with the same equipment). Using what you know about the sight angle and how triangles work the plumb of the column can be determined.

You will still need a plumb bob, but a much shorter one.

In actual practice at one time, during large turbine erections one of the installation checks involved checking the LP hoods to a plumb line. The procedure for aligning the horizontal internal components to a piano wire required the use of a .016" wire with a 30 pound weight. The wire was readily available and was also used for the vertical check. If your only concern is the effect of wind on the wire hang it with a large weight and submerge the weight in a viscous fluid such as motor oil.

As mentioned in an earlier post the check can be made with laser equipment fairly easily.

Is the test using the piano wire as a measuring device or to measure vertical lean of the column?

When the column is free standing, measure the top from 4 points at the same distance from 4 directions. Measure this distance, measure the height and measure to each of these 4 points. Make sure these are at the same level of the base of your column.

You can calculate with 2 lengths and the angle. Or with 3 lengths (easy when you use 3,4,and 5 as pythagoras donkey bridge shows)

On steel columns they also use magnetic telescopes that are fine leveled - sort of like one on a sniper rifle - to look down from the top or vice versa.

We also used a green laser on a perfect level platform to point upwards. Our robot ran the same tract and had a measuring lineal that informed us even on welding deviations, plumb faults and weld thickness.

Lots of good suggestions, but the ' 'verticality' ' of what is to be measured?

What is your preferred measure of verticality? (i.e.: 1 mm in 1 meter?, 90.13 degrees? 1 inch in 10 feet? other?)

Where is it located? (i.e.: on a hill top? down a well? in a wind channel? etc.)

Are there any other physical conditions that would affect the thing-to-be-measured, or the act of measuring it?

Even in a 'windless' location a plumb bob will take a full year to accurately read the verticality at that distance. The earth wobbles. One of the early home purchases I made had a beautiful tiled star burst in the front hallway, but it was not centered in the hall. I noticed that it appeared to be directly below the center of the dome three floors above. I had to attach a plumb bob and was disappointed to see that the bob did not point to the center of the star. I left the bob there for several weeks and noticed that the bob was plotting a series of arcs that defined each point in the star. Over the course of a year the bob visited each point. The circle made by the points was, if I recall, a little under 2ft in diameter. A little trigonometry will give you the min/max error that may be encountered using a plumb bob of 60 meters in length. Mine was about 10m in length. Use a self levelling laser. A good one may only have a deviation of +/- 4°. P.S. The house was stone built in 1847. I seriously doubt too many modern home builders could accomplish such accuracy!

So, you built a Foucauld pendulum of 10m? Cool!!

http://en.wikipedia.org/wiki/Foucault_pendulum

Don't forget that even with a good sized plumb bob, a wire that long may be influenced by the "pendulum effect".......you may not get the accuracy you desire measuring a column with this height.

Hire a licensed land surveyor if this a critical measurement. They have the necessary total stations, including lasers and IR.

Our friends across the pond have more experience measuring vertiicality than we do. They began construction of Sailsbury Cathedral in 1220 AD. About 150 years later they developed the engineering skills to add the 123 m tower. This was not without problems and they made extensive use of piano wire to measure the accuracy and stability of the structure. They finally settled on using laser technology. and if one visits the Cathedral today, one finds a small laser on top of the tower pointed at an ornate target embedded in the floor.

The piano dates from rather later, about 1700. Perhaps the Salisbury Cathedral builders used psaltery wire (the psaltery being a medieval stringed instrument like a miniature harp).

Dear Manikasani,

If you have a laser or total station at hand, use it.

If not, yes, you can use a plumb for 60m height.

I have used 75m for a bucket elevator at cement silos. Less than 5mm deviation.

Regarding the effect of the wind, three considerations:

1. Use a proper weight, according to the wire section. A broken wire can be very nasty.

2. Check the more habitual wind direction. There you will know what is the better position for measuring.

3. Let the weight rest hanging inside a bucket of oil. It will help to damp vibrations or other effects from the wind.

Check as well, prior to each masurement, that the weight has no contact with the bucket walls or the bottom. You will need to retighten/lift more than once per day, maybe for two or three days, depending on the quality of the wire, temperatures, etc.

Salu2 cordiales,

Abel.

It is common knowledge that the piano wire method only works to 48 meters.

Any column heights greater than 48 meters must use a plumb-bob.

http://en.wikipedia.org/wiki/Plumb-bob

I think you can accurately align using long wire with some high density weight even if there is wind drag which at best can make it to oscillate. By watching the mean position of the pendulum to will know the exact location. It may be tricky but it will work.

Many accurate methods have been recommended here, but a big word of warning:

The tower will sway in the wind so the measurements will not be accurate unless the air is fairly still.

may I add that the building deforms also because the sunny side is warmer than the shadowed side. Over the day and over the year those deformations can be quite important (all is relative) and have to be considered as errors. The effect is minimal at night.

I think that one of the more interesting aspects of this project is going to be determining the axis of the structure.

This thing could be a non-symmetrical shape with all sorts of imaginable configurations. It could be designed by an artist in which case who knows what this thing would look like.

The possibility of a challenge exists here.

Test bed for experimentation and technique development, perhaps?

A plumb bob suspended in a bucket of water is commonly used on site surveying. The question is: How precise do you need to know verticality? <1°, <.05°, <.001° or better? Normal surveying with a transit and trig tables is the best.

It depends on how fast the wind is blowing past it, really.