All you Pre-engineered metal building people 1

[Gopher13]

The organization I work for would like to build a pre-engineered metal building at one of our facilities. Up to now, I have never been involved in a PEMB project, but the way I understand it is I design the foundations (piers, foundation walls, footing) and the PEMB folks design everything above. I modeled a building frame to give me an idea of what the loads will be at the top of the piers. I also got preliminary loads from a local PEMB manufacturer to confirm what I modeled and their results are fairly close to mine. The controlling load case for lateral loads at the top of the piers is around 85 kips (LRFD), and the controlling load case for uplift is around 22 kips (LRFD). I am attempting to design the anchor bolts for these loads using ACI Appendix D and HILTI PROFIS software. Both methods produce similar results with concrete breakout strength of an anchor in shear controlling. We have nearly identical (same size, height, and bay spacing) buildings less than one mile from where this building is going to be located. These buildings have much smaller piers than what my design requires. Is ACI Appendix D not used to design PEMB anchors? The other more likely answer is I am doing something wrong, but I don't think so because I come close to matching HILTI PROFIS results. Has anyone encountered this problem before? Any tips? At this point, I am thinking of using a shear lug to take the lateral load.

 

[Ron247]

Does the nearby building have an interior column that yours does not have? That would make a big difference.

How old is the other building? Fdtn design has changed a lot with respect to anchor bolts in recent years.

Compare the brands of buildings. Some PEMB suppliers may specify 1" bolts when 5/8" would work. They minimize the number of standard base plates to make and somewhat stock. They do not care about the diameter to some degree, they are not supplying the anchor bolts just making baseplate holes. They also do not have to figure out how to cluster four 1" bolts that close and make it work in the concrete.

Hope this helps.

 

[lexeng18]

I have designed many PEMB foundations for clear spans over 100’ and never seen thrust reactions near what you are seeing. Are there heavy collateral or snow loads that are causing this?

Regardless, the commonly accepted practice is to design the anchor reinforcement to take the shear and tension loads and ignore tension and shear breakout. The paper I usually reference can be found below:

https://www.sefindia.org/forum/file...nforcement_a_petrolium_project_papers_199.pdf

 

[BUGGAR]

How old are the nearby buildings? I remember the days before Appendix D. We didn't know about all these failure modes then.

 

[TLHS]

You can basically design this using the method lexeng18 is recommending while still staying within the confines of Appendix D by using the supplementary reinforcement provisions.

Alexander Newman's "Foundation and Anchor Design Guide for Metal Building Systems" would be the book to get if you'd like a very well laid out reference with well considered commentary on potential issues.

If you are new to specification of similar buildings, he also has "Metal Building Systems Design and Specifications " which is very good.

 

[AskTooMuch]

You are doing it wrong because you are not considering the rebar for the anchor bolt check.

 

[AskTooMuch]

Get a copy of anchor bolt for petrochemical facilties. It's a good guide to check abolt/concrete piers considering the ties and dowels to resist shear and tension.

 

[Gopher13]

Thanks for all the responses!

Does the nearby building have an interior column that yours does not have?

Nope. They are pretty much identical.

How old is the other building?

2014. Where I am at that one was designed per 2009 IBC. The one I am designing is per 2012 IBC.

they are not supplying the anchor bolts just making baseplate holes. They also do not have to figure out how to cluster four 1" bolts that close and make it work in the concrete.

Although I have been told that the PEMB manufacturer will not design the anchors and that the foundation engineer is to, it seems like this could lead to a lot of change orders. How does the foundation engineer design the anchors without knowing the plan dimensions of the base plate or how big the column is?

Are there heavy collateral or snow loads that are causing this?

42 psf roof SL + drifting from future addition of taller building on one side. Clear span is 80 feet.

the commonly accepted practice is to design the anchor reinforcement to take the shear and tension loads and ignore tension and shear breakout.

Interesting. My understanding is that ACI Appendix D accounts for supplemental vertical reinforcement and ties. The equation for concrete breakout of an anchor in shear has a factor of 1.4 to account for this (at least ACI 318-02 does). Either way, thanks for the paper! I will look it over.

How old are the nearby buildings?

2014....So significantly newer than my copy of ACI 318.

You can basically design this using the method lexeng18 is recommending while still staying within the confines of Appendix D by using the supplementary reinforcement provisions.

I thought Appendix D already accounted for supplemental reinforcing. See my response to lexeng18 above. Thanks for the suggestions of reference books too. I will look into getting them as the organization I work for seems to love this type of building.

You are doing it wrong because you are not considering the rebar for the anchor bolt check.

It seems that way, although I thought Appendix D already accounted for supplemental reinforcing. See my response to lexeng18 above. Thank you as well for the reference!

 

[jimstructures]

Gopher13

If you will share the building width, length, eave height(s), roof slope(s), bay spacings, end wall sections(both ends), bracing locations, unusual building loads, building locations & building codes, I will attempt to generate load cases and load combinations to confirm your reactions. Building regularity makes this much simpler.

Jim (26 years of PEMB experience with a variety of manufacturers)

 

[Gopher13]

jimstructures: I appreciate the offer, but I am not sure how much info. I can share as this is a D.O.D. project. I don't want to get myself into any trouble with Uncle Sam. I am mostly curious about the anchor design. I was assuming ACI Appendix D applies, but it sounds like it does not.

 

[WinelandV]

Interesting. My understanding is that ACI Appendix D accounts for supplemental vertical reinforcement and ties. The equation for concrete breakout of an anchor in shear has a factor of 1.4 to account for this (at least ACI 318-02 does).

I think lexeng18 is referring to Figure RD.6.2.9(a) - Hairpin anchor reinforcement for shear (ACI318-08). This reinforcement is going beyond "supplemental refinforcement" and directly tying the shear force back into the slab, preventing the concrete breakout failure mode.

 

[Ron247]

Gopher:
The PEMB company designs the quantity, spacing and diameter of the Abolts. They give you a baseplate detail similar to below showing the relationship of the baseplate to the structure line (also called steel line, sheet line or girt line). PEMBs DO NOT work off centerline of column in each direction. They work off an "offset" from structure line and one centerline for exterior columns. The work off two "offsets" for corner columns. Only interior columns use centerlines in each direction.

The PEMB does not design the length of embedment of the Abolts nor the design of the Abolt other than the Diameter, Quantity and Spacing

 

[jimstructures]

Gopher13

If you can't share the building information that makes this more difficult. The 85 kip horizontal load is huge for metal buildings in my experience, is it a kickout force or a lateral applied load either wind or seismic? Either way for lateral forces of this magnitude I would consider tension ties, which would reduce the lateral load applied to the foundation and might ease your problems.

Jim

 

[Ron247]

Does your building have interior columns?

If you building is a clearspan, it must be a fairly wide clearspan (150' or more). The big boys (200' or more) have tremendous kick.

On fairly wide clear span buildings, lower eave heights have higher horizontal loads than taller eave heights under DL+LL.

If yours is DOD, your design requirements may be higher than the example building you are reviewing.

 

[dold]

The doc the Lex posted is pretty much a standard procedure where I work. OP, whether you're founding your column on a pier or a slab edge/thickened footing, you should design your reinforcing to confine all breakout/blowout/etc. Are you having trouble with shear strength of the anchorbolts? Make sure - since youre using profis - that your baseplate is flush on the concrete, i.e. no grout. 2" of grout will blow up your anchor diameter. Plus, PEMB are almost always set straight on slab - no grout. You can try a higher grade of anchorbolt. If you try to spec a shear lug i'd expect some kickback from PEMB guys - you'll have to modify their baseplate, or get them to do it but good luck.

 

[dauwerda]

Interesting. My understanding is that ACI Appendix D accounts for supplemental vertical reinforcement and ties. The equation for concrete breakout of an anchor in shear has a factor of 1.4 to account for this (at least ACI 318-02 does). Either way, thanks for the paper! I will look it over.

I believe you are referring to the term defined in D6.2.7 (ACI 318-11) which has to do with if the concrete is uncracked, cracked, cracked with reinforcement, etc. This term is referring to reinforcement that is not discretely designed as supplementary reinforcement for the anchor. It allows you to take some advantage of rebar that is there, but if it still does not get you the capacity you need, you will need to discretely design the supplementary reinforcement as noted below.

If you go on to section D.6.2.9 you will see that it says the following:

Where anchor reinforcement is either developed in accordance with Chapter 12 on both sides of the breakout surface, or encloses the anchor and is developed beyond the breakout surface, the design strength of the anchor reinforcement shall be permitted to be used instead of the concrete breakout strength in determining ØVn. A strength reduction factor of 0.75 shall be used in the design of the anchor reinforcement.

 

[TLHS]

The first rev or two of the Appendix D methodology didn't have the extra bit about explicit design of reinforcement. If you're working off of a 2002 revision it might not be in there.

 

[Gopher13]

I apologize for taking so long to get back to everyone. This was a very poorly timed post by me. I went on vacation for one week a day after my original post.

I think lexeng18 is referring to Figure RD.6.2.9(a) - Hairpin anchor reinforcement for shear (ACI318-08).

Ah. This figure is not shown in ACI 318-02 (the most current copy of I have). It now makes sense why I cannot seem to get a reasonable result. Thanks for the reference!

The PEMB does not design the length of embedment of the Abolts nor the design of the Abolt other than the Diameter, Quantity and Spacing

Thanks for the info. That is good to know. Also, thanks for the details.

If you can't share the building information that makes this more difficult.

What the hay...…..building is 80 ft x 100 ft, 25 ft bays, no interior columns, 14 ft eave height with 1:12 roof slope, IBC 2012, pg = 60 psf with Terrain category B for SL but Exposure Category D for WL (just trust me on that combo.), provisions for a future building of similar size but 10 ft taller that will result in snow drift parallel to the roof ridge, 85 k lateral is a factored load with controlling load case 1.2DL + 1.6SL + .5WL.

If yours is DOD, your design requirements may be higher than the example building you are reviewing.

Example building is also DOD, but as others are pointing out it look like I should get a more current copy of ACI 318 that better defines supplemental reinforcement.

Are you having trouble with shear strength of the anchorbolts?

Nope. Concrete breakout, but as you and others are pointing out, I can design the concrete reinforcing to take this.


dauwerda: Very helpful. Thank you very much!!!

The first rev or two of the Appendix D methodology didn't have the extra bit about explicit design of reinforcement. If you're working off of a 2002 revision it might not be in there.

You are right. 2002 does not have it, and that is my problem. Looks like I finally will have to get a newer ACI 318.

 

[graybeach]

Fixity assumptions may be causing the large foundation forces. I am just learning to work with PEMBs myself and got some advice to make sure to cover this in the contract documents. If the PEMB manufacturer designs for fixity at the column bases, they can lighten up the framing. Requiring the manufacturer to design the building for pinned column bases in the contract documents will generally make the foundation easier to design and construct.