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8" or 10" anchor bolts?

matemike

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I'm about to pour concrete in a couple days for my 30X40X12 +8' lean-to metal building. I am wondering if there is any real advantage to go with 10" L-shaped anchor bolts over 8" L-shaped anchor bolts. It's a $2 difference per bolt for the 3/4" and I'll be using 40 of them. $80 is not THAT much in the grand scheme, just wondering if I'd be overdoing anything by going 10" and could've saved the $80 for a new angle grinder or something.
 
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kwb

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Wtf? 2in of thread isn't enough for the sill washer and nut.
 

readhead

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Very few building companies spec the anchor bolts. That is the responsibly of the person designing the foundation. The building company provides the reactions and then an engineer will take into account the soil conditions, wind load etc and design the foundation and spec the bolts. A36 is a common anchor bolt and two inches is fine as long as the concrete is flat. I usually like to see three inches in case we have to shim a column.

I rarely see anything less than a 3/4" x 16" anchor bolt.

Where did your foundation plan come from? Did you allow for a sheeting notch? Did you drop the slab at the OH doors? Is there a UFER ground? Is the building being inspected?
 
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matemike

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I rarely see anything less than a 3/4" x 16" anchor bolt.
Good to know. I'll be using the longer ones then
Where did your foundation plan come from? The building manufacturerDid you allow for a sheeting notch? No Did you drop the slab at the OH doors? NoIs there a UFER ground? ?Is the building being inspected? Yes

I bought my anchor bolts from the concrete plant. They were a lot cheaper than lowes or H.D.
Thanks. I'll ask them tomorrow. I approached two fastener companies around here though and they're a lot cheaper too.
8" bolts are fine. Just leave about 3-3.5" above the concrete.
roger that. thanks
 

readhead

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[QUOTE 8" bolts are fine. Just leave about 3-3.5" above the concrete.

What makes you qualified to make that call? How many metal buildings have you erected? Have you seen anchor bolts pulled out of the concrete?
 

dbabicky

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[QUOTE 8" bolts are fine. Just leave about 3-3.5" above the concrete.

What makes you qualified to make that call? How many metal buildings have you erected? Have you seen anchor bolts pulled out of the concrete?

I owned my own concrete business for years. Had to sell because of knee's. Poured many of slabs for many of buildings. (Public and Private) Never had anything fail yet.
Just a side note, when the tornado comes through and rips the building down, the plate will still be there attached to the slab. The building may be in the next township, but the slab and plate,(with 8" J-bolts), will still be in place. Been there done that.
 

Duth62

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In hurricane country.
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readhead

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The stamped and engineered foundation plan that you have should specify the bolt size. If it doesn't it is not complete. The building department will pick up on that. If in fact an 8" bolt is speced with a 2" projection then what is important is the 6" embedment. My guess is that the plan shows a piece of rebar above the hook. A 10" bolt with a 3" projection will give you a 7" embedment which is 1" more than the minimum.

A ufer ground is a 20' piece of rebar embedded in the footing. It is required for electrical inspection. If you are not putting in electrical now do it anyway for future use. A sheeting notch makes installing the siding easier.
 

joes169

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Here in WI, residential code calls for a minimum of 7" of embeddment for anchor bolts, so 8" bolts are out if you need to stick them out of the slab 2". That said, steel buildings are en entirely different animal, I'd contact the building manufacturer just to double check first.......
 
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gungatim

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I've never seen anchor bolts used on a foundation sill for a home or shop. Around here there are sheet metal straps that get embedded in the concerete, they fold out and wrap around the 2x and get nailed on...of course, we don't really have earthquakes.

made by simpson strong-tie, and you don't have to worry about drilling holes and lining them up, etc...

edit: These: http://www.strongtie.com/products/highwind/sillplate-foundation.html
 

wssix99

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Your local municipality or the manufacturer should be able to give you the spec for embedment. Usually, they will give you a depth that is a multiplier of the anchor diameter. I came across something that suggested 8-12 times the diameter was a good rule of thumb.

Regardless, 2-3" of depth will probably not be enough. A 3/4" bolt is very strong. At that depth, the anchor will pull out of the concrete (concrete is weak in tension) way before the bolt is even close to yielding. (The bigger the bolt, the deeper you will need to go.)
 

kbs2244

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Lacking a code requirment, it would just be a peace of mind thing.
 

My Old Tools

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No earthquakes or frost line in Brazoria Tx. Even a 6" J bolt will be fine. If it's an F4-5 tornado, it won't matter what bolts you used. What I see most for metal buildings around here are double plates welded up with rebar in between. They are generally made the size of the I-beam that will be welded to them, and embedded to a depth of 6", leaving the top plate at the surface.
 
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David C

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Concrete anchor bolt diameter and embedment depth are determined from the load on the bolt. Generally the capacity in concrete, rather than steel strength, controls the design. For the light loads in wood sill plates the capacity in wood usually controls.

Except for certain limited applications "L" or "J" bolts as they are referred to here in CA, are not allowed by code. Headed bolts are used.

It is generally accepted that one complete thread should protrude above the nut to get full value from the connection.
 
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matemike

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So I picked them up from the building supplier. Good thing I did because the 3/4" bolts were 16" and the 5/8" bolts were 12". They're strange though as they have just a bolt head on the anchor end. No plate or washer of any sort. I may get some washers and have my concrete guy set them with an added washer for more holding power. Any reason this could hurt?
 

David C

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The added washer is often used with an additional nut holding the washer tight to the bolt head. If you don't do this the washer can float up during pour rendering the washer useless.

The washer can increase AB tension capacity but doesn't do much for shear.
 
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matemike

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The added washer is often used with an additional nut holding the washer tight to the bolt head. If you don't do this the washer can float up during pour rendering the washer useless.

The washer can increase AB tension capacity but doesn't do much for shear.

I was afraid of that. Only half of the bolt is threaded, the half near the anchor end is non-threaded so I can't really tighten down on the washer unless I welded it, which I'm not going to do. The bolt head and length of these bolts will be sufficient.

I'm assuming AB tension is anchor bolt tension?
 

wssix99

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I'm assuming AB tension is anchor bolt tension?

Yes.


So I picked them up from the building supplier. Good thing I did because the 3/4" bolts were 16" and the 5/8" bolts were 12". They're strange though as they have just a bolt head on the anchor end. No plate or washer of any sort. I may get some washers and have my concrete guy set them with an added washer for more holding power. Any reason this could hurt?

If your leg of the "L" anchor bolt is 1 1/2", you'll have over 1 square inch of bearing surface area from the bolt surface alone, which should be plenty.

For pullout forces, the concrete fights those in an area the shape of a cone. The sides of that cone are where the concrete conteracts the tension forces. If you added a washer, it wouldn't do much. It would just spread out the cone a little bit, but would not increase the effective surface are of that cone very much. (That could all be calculated, but it's too painful to do that on a Sunday morning.)

bolting_image10.gif


The real strength comes from the depth of embedment. If you want more pull-out force, sink the anchor bolt more. That really makes the cone larger and will give you way more strength than doing something like adding a washer.

If you embed those anchors 12", then you are getting a good bit of pull-out force. Google tells me that the surface area of that cone would be 1000 sq inches. If you assume a 300 psi tension strength of the concrete, that would give you 150 tons of pull out strength. (Let's get crazy and assume that you need a 4X factor of safety, and that's almost 35 tons you can bet your life on.)

The effect of chaining that embedment depth is pretty dramatic. If you only embed 9", you'd have around 90 tons of pull-out force. (So a 1/4 reduction in embedment would loose you more than 1/3 the strength.)
 

David C

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wssiz's diagram is accurate but for a very limited application. AB capacities are a function of AB material properties, the type of concrete, edge and end distances, and EMB depth. The calcuation proceedure is quite complicated and having done it by hand once or twice I use computer programs.

The code proceedure for concrete AB takes up about 50 pages in ACI 318 appendix D. Check it out if you want to verify the difficulty. Increasing EMB depth does not always increase AB capacity and sometimes results in decreased capacity.

I think 300 psi conc tension capacity is a little high and the failure cone shown can be truncated due to edge & end distances, or intersection with other AB cones.

Texas codes may not require much seismic design but this is a metal building and wind loads probably control over seismic. Some prefab steel bldgs design for min steel section at the roof peak. This results in a moment in the roof to column connection. Most metal buildings are designed such that there are dead load moments and shear forces at the col base plate. That is the anchor bolts are in shear and tension when the building is simply sitting on the foundation. For these reasons the AB's are a critical part of your building.

Your foundation designer should have specified the exact bolt; material, dia, and EMB depth. If he didn't he needs to provide that to you. If you use the wrong bolt size and there is a problem you are on your own. You can complain about it wasn't on the plans but that likely won't get you far especially if he points out the requirement was in the fine print somewhere that you missed. And his other argument will be you should have asked. Ask.
 

wssix99

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Your foundation designer should have specified the exact bolt; material, dia, and EMB depth.

My generalized reply assumes the OP does not have a designer and is doing this themselves. I'd expect that if a designer or engineer were involved, the would have provided some sort of spec.
 
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matemike

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My generalized reply assumes the OP does not have a designer and is doing this themselves. I'd expect that if a designer or engineer were involved, the would have provided some sort of spec.

There ya go.
Sorry everyone, I guess a lot of confusion could have been avoided if I did mention that tiny detail.

I'm getting a building that was designed by me, but engineered and being fabricated by a reputable building manufacturer here in TX. It meets 120 mph wind criteria which is all I'm required to have.
The building manufacturer has not put any design detail into the foundation other than the anchor bolt pattern itself and that this building requires a minimum 3000 psi concrete.

I've spoken and visited with several different concrete slab contractors. We've been talking about grade beams, re-bar size and spacing, slab thickness, aprons for run off, psi of the concrete etc. They of course ask for the anchor bolt plan and if they need to make the templates. I request that they do because I've never done this before.

My original question was what length and type of bolts I needed because the building plans are vague saying I just need 2"-2 1/2" of threads protruding. I did end up acquiring the bolts from the building manufacturer. They are hex headed bolts and are 3/4"x16" for the main wall beams, and they are 5/8"x12" for the framed opening beams. I'm quite satisfied that I went with them because they were about the same price as fastener companies were going to charge me for 8" and 10" L-bolts.


Now just to explain my foundation plans: we're going to make 1'x2' grade beams with steel reinforcement around the entire building perimeter. The perimeter beams will capture one side wall, both end walls and the lean-to legs. Then I'll have 1'x1.5' grade beams going across the foundation from top to bottom as well as side to side in a plus sign (+). So one side wall will not have a grade beam running it's length under it, but all three of that wall's supporting legs will land on beams whether it's on a perimeter beam or a crossing beam. Only two framed openings for windows will have their feet fall off of a grade beam, so the concrete contractor has agreed to make a 1'x1'x18" box footer for those areas and set the 12" anchor bolts there. They'll only go about 9.5" to 10" deep so I feel 18" deep is enough concrete for 12" bolts. I've gone with #4 re-bar 16" oc and a minimum of 4" slab thickness, so it will be 4"-5" plus throughout. I'll be going with 3,500 psi concrete, maybe 4,000 psi, depends on the prices the day of pouring. I live in rural Brazoria county Texas, but there are 6 concrete plants within 20 minutes from my house. I'll be calling every one of them the day before the pour to set one up for my pour the next day. My concrete guy is a friend of a friend, and for several reasons to keep his reputation up he wants me to run the concrete order because he's been burned in the past by trucks showing up with less than he ordered and ultimately coming up short for some pours before. So he told me to make the order and to order twice what we calculated for my pour (35 yards, so order 70) and I can just stop sending trucks once we're complete. Does any of that make sense?
 
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wssix99

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I did end up acquiring the bolts from the building manufacturer.

Cool. I'd guess you should be all set then, unless you have any other local codes/requirements you need to address. Hopefully, your manufacturer took all those in to account when they did your design and gave you the bolts! :)
 

WNYflyer

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Very few building companies spec the anchor bolts. That is the responsibly of the person designing the foundation. The building company provides the reactions and then an engineer will take into account the soil conditions, wind load etc and design the foundation and spec the bolts. A36 is a common anchor bolt and two inches is fine as long as the concrete is flat. I usually like to see three inches in case we have to shim a column.

I rarely see anything less than a 3/4" x 16" anchor bolt.

Where did your foundation plan come from? Did you allow for a sheeting notch? Did you drop the slab at the OH doors? Is there a UFER ground? Is the building being inspected?

^^^^^^ this x 10.

As readhead said above,

Typically pre-engineered steel buildings do not show all the anchor bolt detail. They expect the owners engineer to design the foundation for column loads/reactions that that they the manufacturer would supply to the buyer/owner. The manufacturer typically will only show the anchor setting patterns, assumed anchor bolt diameter and material spec. They also indicate their assumed minimum anchor bolt projection above the concrete which is always subject to change by the foundation engineer based upon shimming, leveling plates, possible double nutting, amount of grout specified under the base plates, etc.

If the manufacturer sold you anchor bolts they probaably sold you what you asked for not necessarily what is is really required from a embedment into concrete standpoint. I don't think I ever ran across a pre-engineered building where I didn't agree with the anchor bolt diameter and material spec they came up with. That being said, no manufacturer that I have ever dealt with over say 30years ever provided any information on the portion of the bolt embedded in the concrete and of course the actually length of embedment. They usually have a big note that says "Final Anchor Bolt Design and Foundation Design By Others" ! or something to that affect.

With light weight pre-engineered steel building the foundation design/size is often based upon holding the building down due to wind loads rather than trying to keep it from sinking due to roof/snow loads.
 
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