Anchor Minimum Embedment Depth

[amendale]

Is there a guide to minimum embedment depth for anchors? I have 1" anchors that are only used to resist shear with no tension (equipment support on slide plates). What should I use for embedment depth?

 

[jayrod12]

What kind of anchors? What kind of Loads? What strength of material are you mounting into? Concrete? Block? Clay Brick?

You're missing a bunch of info for even a basic answer.

Most fasteners (or adhesives) come with load tables from the manufacturers that outline capacities that can be modified to account for edge distance, embedment, and spacings.

Call hilti, or simpson strongtie, or ramset (redhead are the adhesives by the ramset company) and get their catalogues.

 

[amendale]

Using cast in place bolts, in conrete (4000psi). The shear loads themselves are low (5kip / bolt), no tension. The bolt size was specified by the equipment supplier, but the depth is up to us. Obviosly you dont need much depth to resist the load, but I am curios if there is such a thing is a minimum embedment depth. Other forums suggested providing enough to develop the strength of the bolt, but this seems like it would be overkill given no tension and low shear forces.

 

[delagina]

12d is the minimum without tension unless it requires ductile design.

 

[jayrod12]

Since you're loading in shear you will want to think about breakout of the concrete if you are near the edge.

 

[charliealphabravo]

What type of equipment is being secured? Are there any vibration or impact loads from rotary or reciprocating action in the equipment? Vibration effects can govern over any static load considerations.

Also a 12D minimum doesn't seem appropriate. What is the reference for that?

 

[delagina]

this is most likely an heat exchanger foundation since it has sliding plate.

12d is from Design of Anchor Bolt for Petrrochem Facilities

 

[amendale]

It's a boiler foundation. 12d would give me a 12" depth. considering breakout and pry out, I only need a couple of inches since the load is so low. Is 12" really necessary?

 

[ztengguy]

I would research an anchor, design it, and if it comes up 2", then use some engineering judgement, and say use 6"

 

[charliealphabravo]

At each anchor bolt location you could provide an embed plate (eg. 8"x8"x 1/2" thick) with say (4) 1/2" studs which would cut your required embed depth in half (if 12D truly applies). Then the 1" diameter rods (short stubs just long enough to carry a nut on both sides of the boiler base plate) would simply drop into a hole in the plate.

 

[somorris]

Since you don't have to worry about pull-out, not much length is really needed. But you have to consider what is practical from a construction standpoint to purchase, get in place and hold correctly while the concrete is poured. I haven't checked to see what length 1" anchors (or simple bolts for that matter) are available in commercially, but I would say use at least a 6" or 8" long anchor. You may have to go with a bolt with a heavy washer. I would be surprised if you can find a regular anchor bolt 1" diameter short enough to meet what you want.

 

[delagina]

if you are not in petrochem industry then i wouldnt follow the 12d recomended by the book.

as far as i know aci doesnt have minimum.

also you may need to be specific coz there are two ways to get anchor embedment, either to develop anchor with pedestal rebar or in your case no rebar consideration.

 

[wannabeSE]

I don't know if ACI 318 has a minimum. But for a point of reference, I have a couple thoughts. Simpson Strong Bolt2 1" expansion anchors may be installed with a 4-1/2" effective embedment per ICC ESR-3037. For seismic equipment anchorage in the 2001 California Building Code (based on the 1997 UBC), the response modification factor, Rp, could be no larger than 1-1/2 when the embedment was less than 8 x diameter (non-ductile). The IBC section 1911 (2009 edition) has a table for ASD that list a 1" anchor bolt with 7" embedment.

Like ztengguy, I would probably use 6" of embedment unless there was some other constraint. Or, I would use the 7" embedment with 5.3 kip ASD shear capacity per the IBC rather than calculating capacity with ACI-318 appendix D.

 

[TXStructural]

At the risk of sounding like a curmudgeon: The difference in cost and time to drill and install for 12" embedment versus a 6" embedment is trivial for any contractor, unless there is a very large number of anchors. They could have been done by the time we stop discussing the merits of minimum depths. Minimums are minimums and going deeper is seldom a risk.

 

[ztengguy]

@ TXStructural, he is using cast in anchors.

 

[TXStructural]

Ah, now I see that. Even more of a reason to go deeper than minimum. The cost of a longer anchor is minimal, compared to the time taken to calculate the nuances of minimum depths.