Stud Shear Connectors 1

[miecz]

Recent discussion about shear connectors led me to look up their shear strength. I'm a little surprised to find that the nominal strength of a shear connector in 5,000 psi concrete is R_gR_pA_scF_u (AISC I3-3), where F_u is the tensile strength of the shear connector. Now, back in ASD days, I used to think of shear yield strength as being some fraction of the tensile yield strength, like 1/[√]3. Is the shear strength of a shear connector equal to the tensile strength of the material?

 

[WillisV]

The failure mode for the studs is actually based on a rupture failure mechanism of them snapping off and is therefore based on Fu. You are correct in that per von Mises failure criteria the theoretical strength of the stud should be around 0.6Fu (which is the rupture strength of a steel shape). However, the stud values provided in the manual are based on real-world testing (push-out tests) which indicate that the tested strength is more in the range of 1.0Fu.

The descrepancy is due primarily due to the helpful effects of friction. The shear is delivered into the stud at some distance above its base, this translates to a moment at the base of the stud which is then resisted by a vertical couple (tension in the stud and compression some distance away within the concrete). The compression some distance away is the normal force that provides frictional resistance in addition to the resistance of the stud itself.

For more info see:

http://cedb.asce.org/cgi/

http://WWWdisplay.cgi?0201320

 

[miecz]

WillisV-

Great answer, thanks for this, and for so many other great posts.

Another question. Please refer to thread507-235455.

If one were to bolt two steel shapes to make a composite per LRFD theory, and then wish to provide A*Fy shear strength, would one use the shear strength of the bolts (AISC Table 7-1), as opposed to the tensile strength (AISC Table 7-2)?