Please refer the problem statement and the part-1, part-2 of this cast in place concrete anchor bolt design calculation example so that you will be in phase with this part (part-3) of the calculation. Here we will calculate the pull out strength of the concrete anchor according to the ACI 318 Appendix D codes.

**What is Anchor Pullout Strength?**

As the name suggests, it is the force required to uproot a anchor out of the concrete.

**Calculation**

According to ACI codes, the pull out strength of the group of anchors is given by

*φN _{pn}=8nψ_{c,P}A_{brg}f’_{c}…………………………………..D-14*

Where,

Φ – Strength reduction factor for pull out strength and its value for non-reinforcement in tension is 0.70

ψ_{c,P }- Modification factor for pullout strength based on the presence of concrete cracks, for the concrete with cracks at service load level **ψ _{c,P}=1**.

n – Number of anchor bolts, in our case **n=4.**

A_{brg} – Net bearing area of the head of anchor bolt in square inch, in our case **A _{brg}=0.654 Square inch**.

f’_{c} – The concrete’s specified compressive strength in psi, in our case **f’ _{c}=4000 psi**.

So, by putting all the values in D-14, we get the pullout strength of the anchor group as

φN_{pn} =0.7*8*4*1*0.654*4000 lb

**= 58598.4 lb **

In the next part (Part-4) of the foundation anchor bolt design calculation example, we will discuss about calculating the concrete blow out strength in tension.

## 2 comments

## irvin

August 7, 2014 at 4:13 pm (UTC 5.5) Link to this comment

hello sir. say im analyzing the farthest bolt from the centroid. and I have edge distances, and all the edge distances are bigger than the hef. shall we still use the hef value? or Edge Distance/ 1.5. Thanks. iris_irvin19@yahoo.com

## MechGuru

August 7, 2014 at 11:37 pm (UTC 5.5) Link to this comment

Still you have to consider “hef” rather than “edge distance/1.5″ because the base radius of the breakout cone is related the “depth of anchor inside the concrete” or “hef”. Even though your edges are far than “hef” still the base radius of the break out cone will be limited by “1.5*hef” hence you have to consider “hef” and NOT “edge dist./1.5″

Hope it make sense