Transfer of forces by thread (Coupler)

[drum]

We have had a problem with a badly specified coupler, used in a holding down system with a gantry. The coupler is used as an interface between two contractors, one constructing the groundworks and another erecting the gantry. The theory is the gantry contractor can thread his studding into the coupler at any time or chhange the gantry in future.

The length of the threaded part of the coupler has been questioned.

I have been trying to understand the theory behind the minimum engagement of thread between the bolt/studding and coupler to transfer the load in compression or tension.

Is there a 'classic' type design theory for this, ie engagement of thread from the studding onto the coupler.

 

[jonralph]

not quite sure what you are asking for but it sounds like your studs are too short. Rule of thumb is there should be at least one full thread showing above the nut. UNLESS the studs are specced to be tensioned rather than torqued. Tnesioning will require a greater length of stud.