Safety Factors for Self-Tapping Fasteners

[brut3]

I have recently prepared some connection calculations where my company will be attaching Aluminum Extrusions to light gauge framing using #12-14 Drill Point #3 self tapping fasteners. Ever since I have been using these types of fasteners I have been using a safety factor of 3 to reduce the average ultimate values given per the manufacturer of the fastener to determine the allowable pullout and shear values.

I have recently had a few engineers question this safety factor and suggest that I use 4 to determine the allowable values. I always point them toward the applicable code that should govern these types of connections (2007 AISI Chapter E4) where it states that a safety factor of 3 should be used to determine the allowable strength or design strength.

I was hoping that someone could verify that I am either using the correct safety factor or point me to where it recommends using a safety factor of 4.

 

[Ron]

The IBC requires a safety factor of 4 for anchorage into concrete; however, it is silent on specific connection safety factors. ASCE 8 and other referenced documents including AISI, require "metal to metal" connections to have a safety factor of 3 on the fastener tension and shear. They are then to be checked for interaction.

 

[sdz]

Actually I think the real problem is with the fastener manufacturers for publishing average ultimate values rather than characteristic or design capacity values.
Or is the problem with us engineers for not insisting on getting appropriate design values?

 

[Ron]

tbruton3...ps, I hope you are isolating the extrusion from the light gauge framing, and using stainless steel fasteners. I assumed the stainless steel fasteners...that's why I gave the ASCE 8 reference.