Example of Concrete Anchor Bolt Design Calculation – Part-4: Determining Side-face Blowout Strength of Anchor in Tension

In this part we will calculate the side-face blowout strength of the concrete anchor according to the ACI 318 Appendix D codes and also consolidate the results of the different types of anchor strengths in tension we have calculated so far.

Please refer the problem statement and the part-1, part-2, part-3 of this cast in place concrete anchor bolt design calculation example so that you will be in phase with this part (part-4) of the calculation.

What is Side-face Blow Out Strength?

In simple term, it is the failure of the concrete due to the closeness of an anchor bolt with the side surface of the concrete foundation. When the anchor bolt is too close to the side then the possibilities are there that before breaking out the top concrete surface, the side surface get broken. While calculating side-face blowout the depth of the anchor bolt and the distance of the anchor from the closest edge are considered.



According to ACI codes, you need to calculate the side face blowout only for the anchors which has the distance from the edge lesser than 0.4 times the depth of the anchor, or

Ca1 < 0.4*hef ……………………………………………4.1


Ca1 – Minimum distance from the anchor to the foundation edge (in our case it is 5 inch)

hef – Effective embedment depth of anchor (in our case it is 10 inch).

So, from equation 4.1, 0.4**hef is 4 which is less than Ca1 so we need to calculate side-face blowout strength for this example.

Summary of Calculated Strength Values in Tension

Through the part-1, Part-2, part-3, and this part we have come out with the following strength values:

Nominal material strength for the anchors (Φ Nsa) = 75150 lb

Concrete breakout strength for the anchor group (Φ Ncbg) = 20694.6131 lb

Pullout strength of the anchor group (Φ Npn) = 58598.4 lb

Side-face blowout strength = NA

Out of these three strength values the smallest one will be the design strength.

So, the design strength in tension = 20694.6131 lb

If you refer the problem statement for this foundation anchor bolt design calculation example then you can observe that tensile load (20000 lb) applied is lower than the calculated design strength in tension (20694.6131 lb), so, the design is safe under tensile load.

In the next part (Part-5), we will discuss calculating the materiel strength or steel strength in shear.


Leave a Reply

Your email address will not be published. Required fields are marked *