Minimum embedment length for anchor rods on a concrete pedestal? 1

[p4blo]

Hello people! I'm new at this and I hope I get some help around.

I'm designing the anchor rods on a concrete pedestal for tension and shear usnig the Design Guides for AISC 01. My result is to use 4 anchors of 1-3/4" of diameter and with that configuration I can manage all the minimal distances on my base plate and pedestal. However i've been searching for a minimum embedment length for those anchors and can't find any.

The design gives me 5" of depth of embedment (hef) using the concrete breakout cone.I found on an old AISC (2nd edition) that for A36 steel (i'mm using that) one should make that anchor of at least 12 times the diameter, but that's and old Manual and i would like to know if there's something more new to it.

I couldn't find anything on ACI318 Appendix D, neither ACI349 or AISC-13th edition.

Does anyone know if that minimum of 12d is still on use? Or has it changed? Or maybe there's not even a minimum?

Thanks!

 

[hello12345hello]

Hi

Please give some information about how much tension and shear load you have. Based on 1.75" dia bolt looks like your tension might be very high. and based on app. D if you are getting hef = 5" But it seems low. what is the size and depth of pedestal?

 

[p4blo]

Hello,

Max Tension = 132 kips
Max Shear = 62 kips

Base plate = 15.74" square
Plate thickness = 5/8"

Pedestal square 23.6"
Pedestal Height 40"

Base plate is embeded on pedestal on center.

Actually the tension requires 2 anchors only, however, tension+shear requires 4-1.75" anchors. Based on my the concrete breakout cone, I would only need a small length for the anchor to work, however my boss and I found on old codes about that 12d minimum and we aren't sure about it.

Thanks a lot!

 

[hello12345hello]

Have you check the Tension capacity for anchor bolt group based on Appendix D (ACI 318) - Concrete breakout strength in Tension ?

 

[delagina]

12d is the minimum recommended per ASCE taskforce for Anchor in Petrochemical Facilities. I dont go lesser than this.

I believe you are designing the embedment wrong for pedestal.

1. Develop the anchor and rebar, Ld.
2. Check the pullout strength per ACI appendix D.
3. Check sideface blowout but usually ignored if you meet minimum edge distance.
4. Check Tension and Shear of Anchor Bolt.

Get a copy of Anchor Bolt Design for Petrochemical Facilities.

 

[p4blo]

Hello, yeah i have. Thats how i get that i dont't need that much of embedment length, i'm just not certain if there's a mimimum length that i should consider and if there is, where does it say.

 

[p4blo]

Ok, thanks a lot guys, i'll check ASCE.

 

[delagina]

also no need to check concrete breakout since you are developing anchor bolt and rebar of pedestal.

132 kips anchor bolt tension is big. You'll be crazy to use less than 12d.

 

[rowingengineer]

Please refer to attached for a discussion on the topic.

How could you do anything so vicious? It was easy my dear, don't forget I spent two years as a building contractor. - Priscilla Presley & Ricardo Montalban

 

[WillisV]

1. There is absolutely no way that concrete breakout will resist 132k of tension with 5" embedment with Appendix D. Re-check your calcs.

2. The standard practice in this case is to extend the anchor rods so the breakout plane crosses fully developed rebar sized to take the tension load.

 

[DWHA]

It is best to develope you anchor bolt to fail prior to the concrete. Ductile failure vs brittle failure. provided you have sufficient embedment, if you add a nut and say a 4" plate washer to the bottom of the anchor, it really does a lot.

 

[ToadJones]

I like anchor plates too....but watch putting them to close to one another and too close to the side of the pedestal.

 

[Lion06]

The heavy hex nuts are typically enough to make the pullout capacity be greater than the tensile capacity of the anchor. It's uncommon (unless maybe using Gr 105 anchor rods) to have pullout control, so a plate is rarely required.

The 12d embedment was an old recommendation out of AISC's base plate design guide. That recommendation is now gone, but we still use it in our office.

 

[ATSE]

Agree with Willis.
Your 5" embed result is way way too short, no matter what code you're using.
Better to use ACI318 chapter 12 (lap anchor bolts to vert bars), not App D.

 

[JLNJ]

You need to develop the tension steel in the pedestal above the intersection of the bolt cone failure cone. This may dictate your embedment depth.

 

[JoeBaseplate]

Can I suggest installation of a trial version of DSAnchor to get a ball park idea of anchor bolt design.

Also take a look at this link:

http://www.structuremag.org/OldArchives/2004/july/From Experience.pdf

 

[RWW0002]

The 2008 Version of ACI 318 Appendix D has a new section regarding development of reinforcemtnt per Ch 12(D.5.2.9). I found the diagram in the commentary and recomendations usefull.

 

[ztengguy]

How do you guys feel about developing anchor rods with rebar, and then ignoring the Ap. D? If a rod is lapped with rebar, and the rebar development splice length is met, and the bar is developed, is that good enough?

 

[Duwe6]

Lap splice is still 30-42 Diameters. Yea a proper lap would work, but why bother. Embedment w/nut & washer is 12 D.

 

[RWW0002]

Ztengguy

As indicated previously, you do not have to "ignore App. D" to take advantage of rebar development. Per ACI 318-08 concrete breakout strength may be replaced by the design strength of reinforcement provided that development length is provided per Ch 12. If one ignores App. d completely, some failure mode other than concrete breakout may control the design and not be accounted for.