Regarding anchor bolt design for pier foundation. 3

[sagan26]

Hi all,

I have a question regarding anchor bolt design for pier foundation.

Structure has 4 square piers sitting on 11' square mat foundation. I am checking the existing anchor bolts of 1'-6" typical square pier foundation for tensile load of 70 kips and shear force of 4 kips in both directions on typical pier. Pier has, 8 #5 vertical bars and #4 stirrups. It has two 1" dia A615 Gr 60 anchor rods placed diagonally and embedded 3'-2" into the pier foundation. The clear spacing between anchor rods on either side is 6" and clear distance to the edge from typical anchor rod is 6" on either side. I checked the anchor bolts for steel tensile strength, pull out resistance of anchor in tension, side face blowout resistance, interaction equation, and embedment depth analysis per ACI 318 Appendix D. Anchor bolts passed for all the above checks except for side face blowout resistance.

I thought of three alternatives,

1: Add two additional hilti anchor bolts embedded 10" into the existing pier as general engineering judgement.
2: Add extra concrete (increase the pier size to 2'6" from 1'6") to increase the side face blowout resistance.
3: Do nothing and check the existing anchor bolts for only anchor strength and embedment depth assuming the pull out resistance and side face blowout resistance is taken by pier reinforcement. Since Appendix D calculations are only for plain concrete.

Can anyone suggest me which one is the best solution?

Any help will be greatly appreciated.

Thanks and Regards,

Sagans.

 

[sandman21]

Use ACI 318-08 D.4.2.1, use the #4 to take out the 4kips of shear load, design the member for shear.

 

[Ron]

#3

 

[delagina]

@3, if i remember right both pull out resistance and side face blowout resistance CANT be taken by pier reinforcement.

sideface blowout is not an issue if you meet minimum edge distance per anchor bolt design for piers.

attach is a good reference for that

 

[sagan26]

Thanks for all your comments.

@delagina, thanks for the reference, i went through the reference and it seems like if provided edge distance is > 6do then side-face blowout can be prevented. In my case, the edge distance is exactly equal to 6in (6X1" dia), is it safe to assume side face blowout resistance is ok or should i check per ACI 318 D4.2.1?.

Thanks and Regards,

 

[delagina]

the reference for side face blowout need not be checked if edge distance is met is just a "rule of thumb".

if your bolt fail in side face blowout per ACI even if you meet you edge distance then that guide is wrong.

but i doubt it, there is probably an error in your calcs.

 

[sagan26]

@delagnia, thank you very much for quick reply.

Please find the attached calculation i performed following the reference.

At your convenience, can you please comment on my calcs, that will be of very great help.

Thanks a lot again.

 

[delagina]

i just did a quick look you only have 2 Abolt?
and you have grade 60 Abolt?

seems like yours doesnt match the "usual" 4-bolt, grade 36 Abolt that reference used.

sorry i dont have time check your calcs line by line

 

[sandman21]

The rebar phi should be .75 per D.5.2.9, which puts your nominal strength slightly lower than required. 69.75kips to 70 kips

delagina, anchor ties can be designed to take side blowout, not pier ties. Pull out rebar does not help as far as I know.

 

[delagina]

also minimum edge distance is 8d not 6d for high strength A bolt (>36ksi) per Abolt design guide for piers

 

[amec2004]

You can find a good anchor bolt design examples at

http://www.civilbay.com

These examples are based on ACI 318-08 Appendix D, with Anchor Reinforcement design using above mentioned reference

 

[transmissiontowers]

If you might ever have to repair these anchor bolts by welding, you might consider a grade 60 ASTM A706 rebar bolt which can be welded with the correct AWS procedure. You might also think about a F1554 smooth bar bolt/rod.

The A615 has little control on carbon content, IIRC and is difficult to weld.

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