Anchor design

[shau1]

Question is about supplementary reinforcement suggested by ACI. This is for a column supposed to be "Fixed" to foundations.Axial load is 16870 lbf(uplift) and moment is 155413 lbf.ft. Using a baseplate 20"x20"x1 5/8", I need 10/12 Nos.
1 1/8" dia bolts and also need about 18" of embedment depth.
The pier size is restricted to about 24". Full breakout
capacity of 35 degree prism can not be mobilised because of close spacing. ACI says that calculations for breakout capacity is not needed if supplementary reinforcement
connecting the potential failure surfaces of breakout prism
to lower parts of structure is provided. Are these supplementary rebars for developing the uplift forces in the
anchor bars ? If so then can I compute the bond/development length by using usual equations for bond
length ?

 

[UcfSE]

I haven't read that in the ACI, unless it is in the 2005, which I do not have yet. Would you mind letting me know the section that is in? What I remember is that you can use a higher phi if you have supplementary reinforcing, but you still have to check breakout.

 

[WillisV]

"Are these supplementary rebars for developing the uplift forces in the anchor bars ?" - Yes.

The way I normally do this is to provide enough vertical reinforcing in the pier to develop a capacity equal to that of the anchor bolts. Hook the reinforcing bars just under the top of the pier and then sink your anchor bolts down far enough so that the vertical reinforcing is developed at the depth that the failure plane crosses them.