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Field Measuring Steel Beam Web Thickness

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waytsh

Structural
Jun 10, 2004
373
I was wondering if anyone is aware of a micrometer that can perform this task. Perhaps something like a disk-brake micrometer? Any suggestions would be greatly appreciated.

Thank you!
 
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If it's a Wide Flange (W) shape, I don't see why not. If it's a tapered shape, like an S shape, it would be tricky.
 
Jed,
He's asking about measuring the web, not the flange.
 
I've used the back end of 6" vernier calipers for measuring the distance from the edge of the flange to the web. OK for flanges less than 12" or so and visually kept the caliper 'level'.

Dik
 
Dik,

I have used that method as well but have had difficulty getting consistent measurements. In some case I have been fortunate and have been able to use web penetrations to get the mic right on the web. Sometimes the hole is too small and I place a small piece of flat steel on the backside of the hole and use my depth gauge from the opposite side. It just seemed to me that someone would make a micromemter in such a configuration that would allow you to reach around 8"-12" flanges and grab a web measurement directly. I have had no luck in my google searches.

waytsh
 
Use a straight edge against the top and bottom flange tips. Measure from the inside of the straight edge to the side of the web. Multiply by two and subtract from the flange width.
 
When inspecting bridges we use a small hand held device called a D-Meter which is an ultrasonis thickness measuring instrument. This is what you need.
 
Thank you for the suggestions. CTW, I would have to do this from both sides as I noticed the webs are not necessarily always centered in three plate construction with these metal buildings. Also, I noticed some slight variations in the flange widths and have had some difficulty getting consistent measurements. Hemifun, many of the webs we are dealing with are very thin, would a device like this be accurate enough to distinguish between say a 1/8" web and a 3/16" web? Once again, thank you all for the constructive input.
 
How about something like Starret Lock-Joint Transfer Calipers? ( For our bridge inspection work, we have a No. 36-24, which will probably reach around 12" flanges. For wider flanges, we have to use CTW's method.

These merely tranfer the distance, which we then have to measure separately with smaller calipers/verniers. Larger models, and ones that measure directly, are available but they get pretty expensive pretty fast.

To find them, I called the local Department of Transportation to ask if they had any. They gave me the Starrett name.

Google searches were difficult. I think the "transfer caliper" terms helped, as well as including dimensions (24", 36", etc.).
 
The ultrasonic thickness tester should be very accurate if properly used. I think they are pricey, though. If you have a non-destructive testing lab available, you might inquire with them. This is commonly used for tank inspection as well.
 
Are you doing enough of this work to justify one of the ultrasonic gauges? Phase II makes one that's about $600. We have their $900 model for testing pipe wall thickness and it's worked well.
 
The ultrasonic gauges are very accurate, if I remember correctly, they measure to within at least 1/100th of an inch, possibly more. You may be able to borrow/rent one from whoever is doing the bridge inspections in your area.
 
Depending on the beam size, if there is no existing hole available, field drill a small hole (2-3" dia.) through the web at the centerline near the point of max moment/min shear, and measure with a small micrometer.

Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask
 
I like the idea of the Lock Joint transfer calipers. I am investigating this option. I'm not saying that I wouldn't like to have the ultrasonic thickness tester but I don't think the budget is going to allow for one right now. This is defintely something to consider in the future. Mike, I have considered your approach in a few locations with a slight variation. I was planning to drill a small hole (~1/8" diameter) in the area where I need to know the thickness of the web then place a rare earth magnet on the backside of the hole and use my depth micrometer on the front side to measure against the magnet. Of course I need to make sure any burs are cleaned off and and the magnet is sitting tight but then I would not have to drill the larger holes which I think the owner would not be to crazy about. Especially due to the number that would be required since it seems like they changed web thickness often in these frames. I used this technique in several locations today where the owner had drilled these small holes for something they had previously mounted and it seemed to work very well.
 
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