Finding center of large i-beam web without specialized tools?

[809]

I know they make special squares that have a little step so you're referencing the flat part of either flange (and not the curvature where the flanges meet the web).

How would I do this if I didn't have access to that specific tool?

I simple tape measure doesn't work because if you're measuring the inside of the beam (esp a big one where the connection between the web and flanges is a big curvature), you have to raise the tape high enough to clear the joint which throws off your measurement because the tape isn't sitting flat on top of the beam.

 

[kaymccampbell]

You just want the center, right? I'd measure across the outside of the beam, find the center, then set a try or machinist square up on the web to drop the calculated center to the web.

 

[kaymccampbell]

Or, set a steel ruler across the flanges. Find the center. Then drop the center to the web with a machinist square set on the ruler.

 

[PCustoms]

How big of a beam and how accurate?

 

[PCustoms]

Set a known block on the flange, thick enough to get you past the radius. You'll need 2, and maybe a clamp or 3rd hand depending on orientation, measure from there.

 

[kaymccampbell]

How big of a beam and how accurate?

It's an I-beam, they're not that accurate.

 

[809]

How big of a beam and how accurate?

Up to W30. +/- 1/16"

 

[PCustoms]

It's an I-beam, they're not that accurate.

I meant how accurate do they need to mark...

 

[readhead]

I have been in the structural steel fab business for over twenty years and all we have ever used is small and large framing squares. You need to be careful but all the connection holes are over sized and there will always be holes that don’t line up perfectly in which case a bull pin or a reamer will be used. This is a common situation during erecting. Trying to be perfect will drive you crazy.

 

[coldh2o]

Just grind the corner off your square to clear the radius.

 

[readhead]

That’s not the problem. He is laying the square flat in the web and trying to stay square to the flange if I understand correctly. A shim equal to the height of the radius will help but the best way we found is to use a sharp flat soapstone running against the square as it is raised above the web.