Tension Control Bolt Tips

Ensuring Proper Bolt Tension on the Job Site

  1. Review the calibration documents for the bolt tension testing device, such as a Skidmore-Wilhelm.
  2. Be sure that testing device is set up with the correct diameter front and back bushings.
  3. Use hardened spacers for longer bolts, DO NOT stack multiple flat washers.
  4. Review the instructions for use of the testing device.
  5. Only use bolts from unopened kegs, that have been protected from the elements, in accord

Installation Problems

Q: A bolt breaks in the threaded portion before the spline shears off?

Answer: Mostly likely the torque co-efficiency value has decreased.

Possible Causes:

  1. Storage conditions allowing moisture, exposure to rain, high humidity, temperatures over 140 degrees
  2. Lubrication of the product beyond “as delivered” condition from the factory. (Use of oil, grease or wax on the product components at the job site is prohibited.)
  3. Adhesion of oils, paints, mill scale, dirty burrs or foreign material on the faying surfaces which may allow rotation of the bolt or rotation of the washer with the nut during tightening operation.
  4. Not properly bringing the connection to the “sung tight” condition before final wrench tightening which may allow for the bolt to rotate, same as hex bolts.
  5. Possible misalignment of the connection members that may prevent proper contact of the bolt head and faying surface.
  6. Exposure to the environment over an extended time period before final tightening.

Q: Spline breaks at the shear groove before joint connection is made or before specified fastener tension is achieved in bolt tension testing device?

Answer: Mostly likely the torque co-efficiency value has become higher.

Possible Causes:

  1. Storage and handling conditions allowing sand, dirt, rust or other foreign material to accumulate on the threads of the bolt or nut.
  2. Rough handling of the fasteners that would cause nicks or gouges on the bolt and nut.
  3. Exposure to environmental conditions that cause rust to form on the threads of the bolt nut or washer face.
  4. Failure to follow AISC procedures for initial tightening in bringing all plies of the joint into firm contact before final tightening. (i.e. trying to draw distorted plies together and shearing the spline before the plies are in contact instead of using “fit up” bolts.) On a TC bolt, the spline will shear off when too great of a torque force is applied. Whereas a hex bolt may be torqued beyond the plastic limit of the bolt without the knowledge of together.


Wrench Problems

Spline does not eject from socket.

  1. Check inner socket for abrasions or upsets. Remove replace socket.
  2. Check inner socket for rust, sand, dirt oil or other foreign material caused by poor handling or care in the field. Clean inner socket and replace if necessary.
  3. Check bolt spline foreign as a result of poor handling in the field.
  4. Check ejector spring for contamination, clean components if necessary. Replace spring and pin if broken or worn.
  5. Check sockets for wear and replace if necessary.

Q: Socket does not engage properly with spline or nut.

  1. Check serrations of the socket for wear and replace if necessary.
  2. Check socket size to be sure it matches the fastener being used.


Tips courtesy of Unytite Inc.

  • Contact Information

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