Turnbuckle adjustment

[mrengineer]

I am designing a hanger rod system for a running track suspended from the roof, and have included turnbuckles in the assembly for vertical adjustment. Is there any limitation in the amount of load that can be on a hanger rod when you adjust the turnbuckle? For example after the mezzanine concrete is in place and the roof joists have deflected I would like to have them adjust the elevation of the mezzanine by means of the turnbuckles.

 

[boo1]

ASTM F1145 and Federal Specification FF-T-791b tabulate the recommended working loads and minimum breaking strengths for each size of turnbuckle body. Safe working loads are listed in AISC Manual of Steel Construction 9th Ed page 4-149. Manufactures should publish their own load ratings.

 

[XR250]

They may have to jack up the slab to take some of the pressure off the turnbuckle to be able to adjust it

 

[WillisV]

The turnbuckle manufacturer will likely tell you that it shouldn't be adjusted under load. The real limit is probably the ability of the erector to actually turn the thing. I have found in the past that if you look at the minimum bolt pretensions in AISC for A325 bolts for the size rod you are looking for (e.g. for a 3/4" dia. rod, the value is 28 kips) , it will give you an idea of the upper limit amount of tension/load that an ironworker could pull up on a turnbuckle. Not a perfect answer, but at least it gives you an idea of what might be possible.

 

[msquared48]

That's what cheater bars are for. The structural kind that is...

Mike McCann
MMC Engineering

 

[paddingtongreen]

Remember that the turnbuckle runs up on two bolts or threaded rods simultaneously. You also have to hold the eyes in their orientation while you turn the buckle.

Michael.
"Science adjusts its views based on what's observed. Faith is the denial of observation so that belief can be preserved." ~ Tim Minchin

 

[NITTANYRAY]

You should note that turnbuckles have a lower capacity than the rods.
If you don't want to upsize the rods, I suggest you specify sleeve nuts instead.
As a practical note, balconies supported by rods can be very bouncy. A classical example was the Russian Pavilion at Expo '67 in Montreal.
I suggest using pipes or tubes as your hanger and provide a shorter length to compensate for the calculated dead load deflection. You should also limit your live load deflection to L/480 to reduce vibrations related to walking or running.