Coefficient C for Eccentrically loaded bolt groups

[FrustratedEngineer]

Please I need help.

I have a connection using shear tab, with shear and axial forces applied.

1. When is it permitted not to consider the coefficient?
2. How can I obtain the value of C? The fast way.

I also made a spreadsheet (see attachment) for instantaneous center method and I am having problems on converging the bolt forces.

 

[appot]

If you have a conventional (non-extended) shear tab then you do not need to consider eccentricity on the bolt group. Conventional is defined as 3" or 3.5" from face of support (weld) to centerline of bolt group. See the shear connection chapter of AISC for more information. I do not have my book in front of my at the moment, but the information you seek is on page 101 (or there about).

The fast way to obtain C is to use the design aides in AISC bolt chapter. If the design aides do not match your bolt pattern, then I would recommend a spreadsheet (I did not open your spreadsheet). Alternatively, you could do the elastic vector method by hand.

 

[nutte]

If you have shear and axial, you should use the eccentric bolt value C. The conventional procedure mentioned is for shear connections, not connections with both shear and axial.