Metal Builidng Column Reaction confusion. GO figure right? 3

[JStructsteel]

So I have some confusion on metal building reactions. It says "Building reactions are shown in the sketch, foundation loads are opposite. They show a sketch for rigid frames, H are to the right, and V is up. So Positive H reaction is outward, and positive V reaction is downward. Would that also pertain to the endwall columns? They dont give a sketch for endwalls.

My second question is about endwall reactions (Not the frames, and it may answer first part too). See attached. For Column C, left column at line 1 I have H = -3.0K for the Wind_left1 case. Wind Press Horz is -5.7K. Would these be added together? If so, I would have 8.7K inward thrust and -14.7K uplift for that column correct? Next is the Wind suct horz load, is that an interior load on the column? Subtract that from my 8.7K inward reactions?

the Wind suct horz and Wind Press Horz dont change signs for the opposite side column, so I am torn on how that is applied. Why for instance at Col line C at the left column the Wind Press Horz inward, but on the opposite side its outward? The Wind_right1 horizontal reaction does change sign, so it makes sense on the right side the load is inward.

Thanks in advance. [URL unfurl="true"]https://res.cloudinary.com/engineering-com/image/upload/v1692238171/tips/End_Wall_Column_Reactions_aicuch.pdf[/url]

 

[DoubleStud]

Hard to decipher without all of the pages but my guess is the wind press horizontal may be the wind force going into the page since that the end wall.

 

[JStructsteel]

Here are the relevant pages of the building to work with. Thanks

[URL unfurl="true"]https://res.cloudinary.com/engineering-com/image/upload/v1692240411/tips/PEMB_Pages_ozceiz.pdf[/url]

 

[straub46]

This is the reaction output from the MBS program, and I always had a hard time reading it even when I worked for the PEMB manufacturers.

Wind_Left 1 is wind blowing to the left as you're looking at the elevation, and probably with the + 0.18 GCpi value. Wind_Left 2 is wind blowing to the left with the -0.18 GCpi. Wind_right 1 & 2 are the same, with wind blowing from the right.

Wind Pressure is likely endwall wind blowing on the column (in and out of the page), wind suct horizontal should be endwall wind suction. Trib out the area based off a quick wind calc for the building if you need to, that should help confirm those values.

Go Bucks!

 

[JStructsteel]

Straub46 thanks. Why for the left wind cases do I get an inward reaction? Even for the frames, which I would not expect.

 

[straub46]

I'm not sure what you mean by inward. Both the outside column lines have reactions in the same direction, showing the column pulling to the left under wind to the left, and to the right for wind to the right. Also, wind to the right/left is as you're looking at the endwall elevation, so from top to bottom in plan, for all the frames.

Go Bucks!

 

[JStructsteel]

Perhaps I have my directions all screwed up. From the frame reactions and sketch, I interpret horizontal loads that are positive are outward (to the left) vertical loads that are positive are downward.

So from that logic, from the end wall reactions, Column 1-C would have 3.0 K inward reaction for the Wind_Left1 case.

What am I missing?

 

[straub46]

The sketches on p.2 show positive horizontal to the right (not inward/outward), so column 1C has a 3 kip load to the left under wind_left 1, which makes sense to me.

There should be endwall bracing between column B-C based off the reactions listed. Wind blows down on the plan (wind to the left), puts the rods into tension, which pulls the base of the column to the right if you're looking at the endwall elevation from the left of the page. The reaction then is to the left, which is listed.

Go Bucks!

 

[JStructsteel]

The note on page 3 says "Positive reactions are shown in the sketch, foundation loads are in the opposite direction"

I interpret that as a positive vertical dead load is downward, positive horizontal is outward.

Perhaps I better call them, lol

 

[JStructsteel]

UPDATE: straub46 was correct.

I did call them. The frame convention does not apply to the wind load, lol. He said you wouldnt know that unless you called them.

For the End Walls, the Wind_left, Wind_Right is due to the cable bracing pulling the columns along the line. Wind press Horz and Wind Suck Horz are the pressures into and out of the bulding.

Ay Yai Yai.

That industry needs to do better. Much better. If I sent crap like that to a client, i dont think they would be a client much more.

 

[Aesur]

Glad you got an answer! The answer is in line with how I would read that as well, but I have done more of these than I care to have done. Normally output from the major PEMB manufacturers include 3 loads for each columns Hz, Hx and V so it's a bit easier to distinguish which is in line with the frame and which is out of plane to the frame. I had never seen one such as you shared, so thank you for sharing that in case we come across that as well.

I agree the industry needs to do better, but it is my understanding they give what they give because lawyers tell them too to shield them from liability. It's a shame because I suspect we often times oversize foundations. I have tried many times, even proved it a few, that a conventional building can be cheaper or sim in price to a PEMB, because with a PEMB they just push a lot of the costs to the foundations and custom finishes to make it look like a conventional building, at least locally.

The only way the industry could change is if ALL engineers were to refuse to do PEMB foundations, but that will never happen as they are too easy to make money on.

 

[DoubleStud]

Also the way they anchor these things prior ACI318 Appendix D no longer works. It seems the only way to make it work is if you use a hairpin into the slab. If there is no slab, like the large horse barn I just did, you have to make the pedestal quite big.

 

[RWW0002]

@ DoubleStud - These anchors have been discussed on here several times. A quick google search on the use of pier ties to resist breakout and pier dowels to resist tension is worth it. the link below is a bit outdated but has some useful information. some of this has been codified in the later editions of ACI318.

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

I generally can get the anchors to work without too much trouble as long as they are cast-in-place. It is those pesky missed anchors that they want to epoxy into place (on a 3x3 pattern with minimal edge distance) that give me heartburn.. I wish PEMB companies would adopt minimum patterns that meet epoxy anchor minimum spacing as a standard..

 

[JedClampett]

I wish PEMB companies would adopt minimum patterns that meet epoxy anchor minimum spacing as a standard..

What's in it for them? Building to code? Helping out their fellow engineers? A safer design? Making the building slightly easier to lay out?
I've given bolt patterns (ignored) and asked them to design their own concrete attachments (laughed at). I'm now just prepared to get zero cooperation from the PEMB supplier and go from there.

 

[Rabbit12]

Love your post Jed. PEMB's are the worst.

 

[Aesur]

I tend to use hairpins at wind columns, unless I have bypass girts which gives me more edge distance to deal with the out of plane loading. For uplift, I check anchors, which usually only work if I have a large enough pedestal that extends outside the building (rarely acceptable), I have bypass girts which gives me an additional 6 to 8 inches of edge distance, or am allowed to use PAB's or sim and attach to the footing, which is almost always misplaced or completely ignored, so my default lately has been to just require hairpins for thrust, tie beams if needed, tie beams between braced frames or portal frames and embedded plates with rebar hooked over and developed such that it's bearing upwards on the concrete engaging the reinforcing to drag to the footing.

 

[RWW0002]

I've got a pretty decent relationship with a couple of local PEMB companies who will play ball (especially on design-build work). They are great to work with.

Even beyond these cultivated relationships, I generally find that if you can get past the salesman and other middle men the designer/engineer is usually easy to get along with and can be very helpful. Sometimes I have pushed back on certain detailing methods for PEMB only to find out there is a very real reason for the standard (standard punch dimensions, manufacturing ease, etc.) Other times they have modified designs to meet my recommendations for easier anchorage or other special detailing items. They are not all bad.. You just gotta get to the right person.

And then there are the select few that just want to stay ornery.. plenty of those too.

 

[SandwichEngine]

PEMBs are awful. We have a job in house where their floor beams attach to our structure. The just gave us a vertical load. No breakout between dead load, live load and any other load. No mention of whether or not the loads have been factored or not. They just expect you to intuit what they're thinking or you have to call them to get them to explain. They obviously will have people who have worked in consulting engineering so it's not like they don't have a good understanding of what we want to see. I don't know why they just refuse to provide it. As others have said, there are definitely lawyers at play but I truly believe that many of their engineers are intentionally choosing methods and systems that make it harder for everyone else.

 

[straub46]

They obviously will have people who have worked in consulting engineering so it's not like they don't have a good understanding of what we want to see.

Actually, when I worked at a design office for one of the major PEMB suppliers, I was the only engineer on a staff of 20 that had any experience outside the PEMB industry. It's extremely common for PEMB engineers to either be 1) straight out of school, with 0-4 years of experience or 2) have 10-15 years of experience, but have been in the PEMB business their whole career.

The hardest part about working with the PEMB manufacturers is usually all orders have to go through a certified builder (at least for the big name manufacturers). The builders are just specialty erection firms generally, who might have a PM that looked at the EORs loading specifications prior to sending it over to them. I always tried to make sure the loading made sense, but the design contract is based off a document that's usually put together by a erection firm PM and a PEMB salesman. Once it's signed and quoted, it can be a giant pain to get things changed.

Go Bucks!

 

[ntattose]

The reactions can be a bit confusing. You can look at the reactions and their signs for the
dead load only case. You know direction of the reactions for this load. This will help you keep
the sign convention straight. Also, you can request the PEMB supplier provide you with MAX and
MIN loads. These are based upon ASCE load combinations and it will save you from having to calculate
them.