Z Purlins - Revisited 1

[LPPE]

I have an existing PEMB, built by American Buildings. At least I think it was. Old logo on the building says American, and the roof Z purlins are 9.5" deep. The only PEMB company that makes 9.5" deep Z purlins is American Buildings, as far as I know.

Anyway, my client wants to add parapets. This creates new snow drift loads. For an old roof with no parapets, obviously my existing 9.5" Z purlins will not work. The standing seam roof also does not work. I need the Z properties to figure out the best solution.

When I was on the scissor lift investigating the building, I measured the purlins depth and width, but that was it, figuring it would be a common shape, and I could easily find the section properties. Well, was I wrong. I have tried contacting American Buildings several times with no luck.

Does anyone out there have section properties for American Buildings 9.5" Z purlins?

And yes, I already have the CFS program by rgsoftware. Would work great, but I only have the height and width of the existing Z purlins, and I don't want to rent another scissor lift to get the other properties!

Thanks

 

[dik]

It is unlikely that your PEMB can take loading in addition to what it was designed for.

Dik

 

[LPPE]

Understood, Dik. In addition to reducing load on the existing Z purlins, I know the girders will need reinforcing too.

At some point, you have to think it'd be more cost effective to demolish the existing building and build new.

 

[JedClampett]

There's been numerous threads discussing remodels on PEMBs. You could probably do a search. But the bottom line is that these are very difficult creatures to work on. You've hit a pretty normal roadblock (section properties). Next one is going to be material properties. After that, you're going to check the building for the loads in the current code, without the parapet, and like dik says, it won't work. So you'll do your research, eat up more time, pull the codes from whenever it was built and lo and behold, find out it doesn't work for those loads either. You're going to have to measure the frames, which are likely tapered and figure out varying section properties for them. As you said, there's a point where a new building is cheaper.
And the funny thing is, the original designer won't be any help, unless the building falls down and than they'll immediately be real helpful and say that whatever remodel you did, no matter how insignificant, was the problem. Stuff that we do without blinking causes PEMB's to fall down.
Be sure to remind the owner how much they saved on the initial building. Ask them to use that savings to pay you.

 

[msquared48]

I agree here. Parapets on the P{EMB are defeating the original purpose of the PEMB - to save material.

Mike McCann
MMC Engineering

 

[dmoench01]

LPPE - Here are the girts from American. I work with them frequently.

 

[LPPE]

Eureka!

Thanks a million, dmoench01. Much appreciated

 

[dik]

The girts are only a small part of the puppy... you will find the frames the most 'interesting'... may you live in interesting times...

Dik

 

[LPPE]

This isn't my first time to the rodeo. I do wish that my employer had some sort of policy about existing PEMBs. Something to the effect of "We won't touch it with a ten foot pole, or a 10x multiplier on our normal fee".



Even the flanges of some of the girders change thicknesses at quarter points....

Another odd item - the flanges of the built up sections (girders or columns) are only welded to the web on one side... You measure the depth on one side of the girder and its 28.75", and then 28.25" on the other.... and some of the webs are ultra-thin...

 

[ARS97]

Well, regardless of what your employer's policy may be, YOU have to be comfortable with it. I've been in your shoes before...I had to analyze an existing PEMB for an increased drift load due to a nearby addition. It was a nightmare. For the life of me, I don't see how anyone can get the numbers to work on those buildings. I live and work in an area where we have some fairly severe winters (southwestern PA & western MD) and you wouldn't believe how many of those PEMB collapse on a regular basis around here. You get what you pay for.

 

[ztengguy]

if you have the dimensions, there is a way to calculate it in cad, or by hand if I remember College.

 

[dcarr82775]

Stop being so mean to the PEMB folks. You can make them work real easy if you follow their design rules:
- Shoot for 1.05 demand/capacity ratio
- Use an Fy at least 1.1*specified Fy
- Ignore any and all rational requirements on the strength of a brace to prevent LTB
- Be inconsistent in loadings so that purlins are continuous but loads to frames are based on simple spans.

I find if you do all that you can normally make them 'work'.

 

[Archie264]

dcarr,

Many of the metal buildings are descended from pole barns, which seem to work despite themselves. (Until they don't that is.)

 

[msquared48]

And pole structures were invented in Poleland. What can I say?

Mike McCann
MMC Engineering

 

[Forensic74]

FWIW, here's what happens when you dont account for drift loads when these buildings are modified

http://www.nwitimes.com/news/local/...cle_20170b2e-70c6-522a-ba97-27d7a22ac503.html