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How To Torque Bolts When Using Unistrut Fittings

How To Torque Bolts When Using Unistrut Fittings

We recently fielded a question about how to properly torque Unistrut fittings.

Applying too little torque can prevent the connection from developing its full load capacity (vibration or movement can loosen the connection).  At the other end of the spectrum, applying too much torque can permanently damage bolts or deform channel and other components.  Based on years of field experience, we have developed some basic bolt torque guidelines for Unistrut applications.

For non-through bolt connections (e.g., channel nut connections), consult the table below:

bolt torque

Although adhering to the guidelines outlined above should yield a secure connection, some disclaimers are in order.  For starters, the accuracy of commercial torque wrenches varies widely, and it is up to each installer to ensure proper bolt torque.  In addition to using a properly calibrated torque wrench, the values above assume a clean, dry (non-lubricated) Unistrut fitting, bolt, and nut.  A lubricated bolt or nut can cause extremely high connection tension, and MAY lead to bolt failure.Unistrut installations with “through-bolts” require special torque considerations compared to channel nut torque requirements. Unlike channel nut attachments, through-bolt connections like the ones shown below induce a compressive load into the channel sidewalls, and the torque must be set to avoid sidewall buckling.

2

Torque values for through-bolts are a function of:

  • Channel bearing strength to avoid sidewall buckling
  • Nut factor coefficient of friction (K) – assumed 0.22 for EG plating
  • Distance from the through bolt to channel end

12
Single Sided Channel Through-Bolt Torque Limits

13
Double Sided Channel Through-Bolt Torque Limits

Remember, the best design and Unistrut materials are of little value unless all of your fasteners are torqued properly.  If you have additional questions, contact Unistrut Service Company for further assistance.

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