Pre-Engineered Metal Building - general considerations for openings
Pre-Engineered Metal Building - general considerations for openings
(OP)
Hello, thank you for any feedback in advance.
Existing PEMB Description
360' wide (6-span frames) x 300' long (12) bays
Eave at 23', Ridge @ 33'
1" dia. X-bracing with hillside anchors. Bracing located at (4) of the (12) bays on each end wall. Probable that (1) or more were removed.
8" "Z-shaped" girts at 5' on outside face of frames.
8" "Z-shaped' purlins at 5' at the roof with wind-bracing.
C8 eave strut with 8" strut-purlin at end walls.
Pretty standard.
What's been proposed is to remove ALL the X-bracing on one side to permit 14' wide x 16' high overhead doors in the center of the 25' bays.
I'd like to get some ideas and general considerations on restoring the building's lateral system and creating the openings.
Existing PEMB Description
360' wide (6-span frames) x 300' long (12) bays
Eave at 23', Ridge @ 33'
1" dia. X-bracing with hillside anchors. Bracing located at (4) of the (12) bays on each end wall. Probable that (1) or more were removed.
8" "Z-shaped" girts at 5' on outside face of frames.
8" "Z-shaped' purlins at 5' at the roof with wind-bracing.
C8 eave strut with 8" strut-purlin at end walls.
Pretty standard.
What's been proposed is to remove ALL the X-bracing on one side to permit 14' wide x 16' high overhead doors in the center of the 25' bays.
I'd like to get some ideas and general considerations on restoring the building's lateral system and creating the openings.






RE: Pre-Engineered Metal Building - general considerations for openings
I recently did a job where we replaced cross bracing with pinned-base moment frames. But it was rather expensive.
RE: Pre-Engineered Metal Building - general considerations for openings
They are so crazy efficient that the least little change, sometimes including typical cyclical code changes, are enough to require major modifications.
In our case I introduced tilt panels as a new lateral load system and reworked quite a few columns and beams.
A great deal of work, and not to be entered into on a quoted rate. I strongly suggest you charge your client for actual effort expended/take this on as an hourly engagement.
RE: Pre-Engineered Metal Building - general considerations for openings
Mike McCann, PE, SE (WA)
RE: Pre-Engineered Metal Building - general considerations for openings
The greatest trick that bond stress ever pulled was convincing the world it didn't exist.
RE: Pre-Engineered Metal Building - general considerations for openings
RE: Pre-Engineered Metal Building - general considerations for openings
RE: Pre-Engineered Metal Building - general considerations for openings
The greatest trick that bond stress ever pulled was convincing the world it didn't exist.
RE: Pre-Engineered Metal Building - general considerations for openings
Not that I disagree with you but let's just say for the sake of argument that the moment frames aren't quite stiff enough. They are still going to have some contribution no? Would you actually go so far as to look at the building as a 3 sided structure?
I think if your moment frames limit your building drift accordingly then they would (should) be stiff enough.
RE: Pre-Engineered Metal Building - general considerations for openings
For this issue, code drift limits are not the relevant parameter. It's about the ratio of moment frame stiffness to braced frame stiffness.
The greatest trick that bond stress ever pulled was convincing the world it didn't exist.
RE: Pre-Engineered Metal Building - general considerations for openings
RE: Pre-Engineered Metal Building - general considerations for openings
Perhaps the roof is discretely braced rather than metal deck? That would change the flavour of the analysis.
The greatest trick that bond stress ever pulled was convincing the world it didn't exist.
RE: Pre-Engineered Metal Building - general considerations for openings
RE: Pre-Engineered Metal Building - general considerations for openings
The greatest trick that bond stress ever pulled was convincing the world it didn't exist.
RE: Pre-Engineered Metal Building - general considerations for openings
RE: Pre-Engineered Metal Building - general considerations for openings
I got lucky the one time that I did this. I had a loading dock retaining wall in line with the braces that I removed. We threw in an external HSS brace over the retaining wall, tidied up some drag struts, and called it a day. It was pretty economical if not particularly attractive.
The greatest trick that bond stress ever pulled was convincing the world it didn't exist.
RE: Pre-Engineered Metal Building - general considerations for openings
What did you do for anchorage in that situation?
RE: Pre-Engineered Metal Building - general considerations for openings
The greatest trick that bond stress ever pulled was convincing the world it didn't exist.
RE: Pre-Engineered Metal Building - general considerations for openings
RE: Pre-Engineered Metal Building - general considerations for openings
RE: Pre-Engineered Metal Building - general considerations for openings
@AJH: I should clarify that I wan't proposing a three sided system. Rather, I was warning that, if the diaphragm were rigid and the moment frames not sufficiently stiff, the building would approach three sided behaviour to the chagrin of the designer. The roofs of these buildings are generally rod braced and therefore treated as flexible diaphragms, right?
The greatest trick that bond stress ever pulled was convincing the world it didn't exist.
RE: Pre-Engineered Metal Building - general considerations for openings
RE: Pre-Engineered Metal Building - general considerations for openings
The greatest trick that bond stress ever pulled was convincing the world it didn't exist.
RE: Pre-Engineered Metal Building - general considerations for openings
RE: Pre-Engineered Metal Building - general considerations for openings
RE: Pre-Engineered Metal Building - general considerations for openings
1) Assume that the columns are fixed at the low beam.
2) Hand pick columns based drift limits and Ix. Give yourself some wiggle room (~15-20%).
3) Run the frame in SAP/RISA/RAM to check the strength of your members.
4) Iterate and optimize for as long as there's low hanging fruit to be picked.
What document is it that you've posted the excerpt from? I'm not familiar with it but it looks interesting. The moment framing in the sketch looks like something proprietary?
The greatest trick that bond stress ever pulled was convincing the world it didn't exist.
RE: Pre-Engineered Metal Building - general considerations for openings
I also added the other schematic of a Full Height Portal frame from a book Metal Building Systems.
The pavilion is for a building I'm glad I'm not dealing with.
RE: Pre-Engineered Metal Building - general considerations for openings
The greatest trick that bond stress ever pulled was convincing the world it didn't exist.