Length of Pipe that Can Fit in Open-Web Joists?

4/26/2019

The other day there was a good discussion on pipe that can run within the open-webbing of steel joists.

Is there a good rule of thumb or any references to determine how long a pipe can be to fit within the joists?

I'm wondering if there's some tool or resource that says for 16" joists that has 2" web spaced at 4 feet, I can use only a 10.5 foot pipe length. It may not exist, just curious if it does already in some fashion.

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4 Comments

Wayne Ammons

4/26/2019 06:45:54 am

There is an old formula and diagram for this. I could not find a website that showed it and am not sure the best way to get it to you, so I have copied an excel file to Dropbox that has the formula and diagram:

https://www.dropbox.com/sh/p4pqnz3d0tmhy1m/AABXIR6uNnXlMzLTuu0zW8vJa?dl=0

steve bahr

4/26/2019 10:24:49 am

I will look around. I have charts that show all of this. Somewhere...

James Phifer

4/26/2019 10:36:10 am

I have used a formula in the past that was created by Ed Miller from AFSA back in 1992. It's a bit conservative but at least I know the pipe will fit.

A/6 multiplied by B
where A = depth of bar joist expressed in inches
B= distance between the bar joist expressed in feet

Example: 18" bar joist spaced 4 feet on center

18/6 = 3
3*4 = 12 feet. 12 ft is the longest length of pipe that will fit.

Bobby V

5/8/2019 04:52:53 am

When I was designing, the rule of thumb was to use 10’-6” pipe lengths for exposed construction installations. For a new system installation in an existing building with hard ceilings (or lay-in), I would use 6’-0” pipe lengths. However, always consult with your installing foreman, they are the experts.

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