Anchor Rods in Tension and Bending - Question

[Jalbno]

Hi everyone, I have a question regarding a clause in the CSA S16-14 code.

I am designing some anchor rods and baseplate for a column. Clause 25.3.5 States that the anchor rods must meet clause 13.9.1 requirement where the moment resistance of the anchor rods is MR = θAR*S*Fy.

Clause 13.9.1 is the axial tension and bending interaction clause stating (Tf/Tr) + (Mf/Mr) < 1.0

My question is, if the moment is applied to the baseplate from the column, would the Mr in this case be multiplied by n (the number of anchors) and not just the moment resistance of a single anchor?
Does the same go for The tensile resitance Tr? Most of the anchor would be resisting the moment and tension, why does it seem like we are required to resist it with only a single anchor?

Thanks for your time.

 

[JLNJ]

The moment is the moment from the point of applied shear to the top of the pier, right? This is what causes moment in the anchor rods.

It sounds like you might be confusing this with the moment in the column. The moment in the column is resolved into T/C on the bolts and a shear force at the base plate level. This is a critical and fundamental principle of column anchorage.

Draw yourself a free body diagram of the column base and then a bolt to get a better visual on what’s happening here.

You also need to decide on the mechanism of the shear transfer to the pier, how many of your bolts resist the shear (to be able to calculate the moment), what role the grout plays, etc.