Stud length in composite steel beam capacity

The studs are there to provide sufficient shear transfer to get the partially or fully composite section. If you consider the ACI provisions for anchorage and specifically the shear strength of anchors in concrete, you can explore how the embedded length of the anchor effects the strength and failure modes.

Shear strength does not continue to increase with embedment length indefinitely. Follow the AISC requirements to get the strength that matches the assumed Anchor Capacity in shear Qn.

The composite beam method used in the AISC tables relies on developing enough shear capacity with the studs so the overall strength of studs in the composite beam is proportional to the strength of the beam up to a limit.

The trick to this, I think, is recognizing that we assume the predominant structural behavior of the connection to be as shown below. In this context, there is no primary tension on the stud really. It's almost more of a shear lug. You still want some tension compacity in the stud nearby, however, lest the slab lift off of the beam under this model.

Good prior discussion of similar issues: Link

The AASHTO LRFD bridge design spec requires studs to have at least 2 inches concrete cover above, and they have to extend at least 2 inches into the deck.

Also:

AASHTO LRFD said:

The ratio of the height to the diameter of a stud shear
connector shall not be less than 4.0.

Click to expand...

Rod Smith, P.E., The artist formerly known as HotRod10