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Measure Bridge Girder Camber - Scanner?

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(@leegreen)
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We are brainstorming new ideas to safely, accurately, and timely measure girder camber on a large bridge project. Bridge is several miles long and 10 girders wide. Need 3 measurements at 20th points (about every 18ft) along each girder at top.

Option 1) Manually measure along girder to layout every ±18ft, then perform a digital level run.

Option 2) Use 0.5" Robotic Total Station with 360° tracking prism on a trolley along top flange of girder, set to measure at constant distance interval.
- Trouble is the safety lines on bridge have threaded rod lying on top flange, so trolley would need to navigate over and around the safety lines.

Option 3) Low flight UAV with GPS and a Camera / Scanner.
- Would this be able to meet accuracy requirements (1/4") needed to for girder camber?

Looking for ideas/input and/or suggestions from others with experience here.

 
Posted : 21/05/2015 9:37 am
(@squowse)
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Reflectorless total station underneath?

 
Posted : 21/05/2015 11:13 am
(@leegreen)
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Forgot to mention.

This bridge is over a river.

 
Posted : 21/05/2015 11:15 am
(@imaudigger)
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How wide are the girders?

Have the girders already been erected?

Will you come in after all of the girders have been erected, or will this be a moving process?

Are you working for the agency or the contractor?

EDIT: What type of girders? Steel I beam or concrete "T" Bulb?

 
Posted : 21/05/2015 11:33 am
(@leegreen)
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> How wide are the girders?
Width varies from 3ft to 5ft

> Have the girders already been erected?
Girders are assembled in ±350ft untis, then set between piers, then erected on site to 1750ft span between expansion joints.

> Will you come in after all of the girders have been erected, or will this be a moving process?
Will need to measure after each 1750ft span is erected.

> Are you working for the agency or the contractor?
Agency

> EDIT: What type of girders? Steel I beam or concrete "T" Bulb?
Painted Steel I beam 12ft Tall

 
Posted : 21/05/2015 11:57 am
(@imaudigger)
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> Girders are assembled in ±350ft units, then set between piers, then erected on site to 1750ft span between expansion joints.

DO you have a profile view to upload?

I don't have a lot of experience with big bridges like this and hopefully some more experienced construction surveyors will contribute.
With that said...a few thoughts. Obviously if your crew will be working on the bridge, make sure they have recently taken OSHA approved fall protection training and have access to gear that has been inspected recently. Make sure they are comfortable with the task at hand.

3' wide girders are pretty easy to walk. The contractor will be responsible for providing safe access for inspections, but timing will be important. Early on, I would schedule a meeting between the RE, prime, and structural steel sub. They will have an idea of what fall protection they will employ as well as the scheduling. Many times the system moves ahead with the work.

Usually the flanges have all kinds of clamps on them, so I'm not sure the trolley would work very well.

I would probably look into something similar to the Topcon Millimeter GPS system.
RTK would reduce the required control to vertical benchmarks on the false work. It would also reduce the number of times you would have to walk the girders.

I would set up the girders as alignments and have the DC alert you audibly when you approach the desired station. That way you can keep your eyes where they need to be.
Mark the station with a stick, take the shot and move on.

 
Posted : 21/05/2015 2:36 pm
(@leegreen)
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No temporary PEDs or cables. Piers at 350ft. Expansion Joints at 1750ft.

But the mmGPS is a great idea. I own one, just never thought to use it on bridge work. I think it will work well. A bit heavy, but I can measure the entire 1750ft span in one setup. The mmGPS transmitter reaches 1000ft. So I can set in center of span.

We'll give it a try. I also have access to Topcon Sirius Pro UAV to test.

 
Posted : 21/05/2015 3:34 pm
(@alan-chavers)
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Lee, this is very interesting. If you have time, could you keep us updated periodically-maybe with some pics?

 
Posted : 23/05/2015 3:49 am
(@leegreen)
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Alan,

Sorry but I will not be able to do that.

 
Posted : 23/05/2015 6:13 am
(@imaudigger)
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I'm curious as to what the accuracy specs are at 1000' range. Also at that distance, curvature will come into play. Does the Topcon system do this automatically for you?

It may be of benefit to record some temps as well. Long lengths of steel do some pretty amazing things with large shifts in temperature.

 
Posted : 28/05/2015 8:24 am