pre-engineer building terminology

[PSUengineer1]

Hi.

I have a pre-engineered building (about 25x60) with steel frames spaced about 5 feet on center. Frames are constructed with tube steel. The frame is continuous at ridge. The ridge condition is shown in attached photo. What is the general terminology used to describe this condition of the frame at the ridge? Thanks.

 

[jayrod12]

I would say that's cold-formed tube bending. Also, I wouldn't be comfortable considering that fully continuous due to the clear change in moment arm between the flanges. That must be a tested assembly, I can't imagine it's a first principles type of moment frame.

 

[Ron247]

I also would not consider it fully continuous. Due to the bend, the Ix would be drastically less than the unbent member. Where the column meets the rafter at the eave, do you have a diagonal brace that runs from the column to the rafter?

 

[XR250]

That must be a tested assembly

I have seen a few of these CF structures with some highly sketchy engineering. I would def. ask for the testing data or calculations (which may not even take into consideration the loss of section depth)

 

[LittleInch]

The terminology? -" An unholy mess.

That doesn't look continuous at all given the line at the centre unless that's a tear in the member?

what a cheap and nasty way to join two square columns together.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[Eric C.]

I've seen that a lot in those prefab, install in an afternoon "garages". To avoid the natural disaster rush the ridge comes "prefailed".

 

[dhengr]

PSUengineer1:
That is some sort of a crimped, semi-pinned (low fixity or moment cap’y.) joiner connection. Boy is that a mouthful. There is most likely a pre- bent connecter bar or tube inside, maybe slightly press fit into the two outer crimped tubes, to keep them aligned and generally in contact with each other. Maybe some final crimping in place, maybe a couple screws or through bolts? The two part (left half and right half frames) are kinda like a gable frame, but pinned at the ridge. They act kinda like a three hinged arch, in gable frame form/shape. We know nothing about the knee details of those frames, those will be the highest stressed regions on the frames, or any bracing systems, you haven’t shown us that. I’ve not seen that exact detail before, but I’ve seen those light cover structures before, to cover boats, farm machinery, cars, etc. They keep most of the rain off, they slough some snow sometimes, given their shape, and they blow over or lift-off fairly easily.

Pre-engineered may be a bit of a misnomer, and suggest that there may be some real engineering calcs. and package behind them somewhere. Pre-manufactured, kit built, framing system or framing package may be more applicable. Ask them for a set of P.E. stamped engineering drawings and see what you get. Ask them for a stamped letter/report, stamped by a P.E., certifying that those structures meet the local building code and see what you get. I’ll bet you won’t get them to call that a code compliant building system. It’s a cheap storage shed, but they don’t like calling it that.

 

[Ron247]

I can't tell if that black vertical line is a cut or a line made with a permanent marker ( "a magic marker" for us old folks) to show where to locate the bender. If it had been a cut, I would think the gap at the top would be a lot wider than the bottom after them bend was made. Also, I do not see a cut on the rear of the underside.

I bet a lot of the design parameters for allowable are from testing and not from calcs. I have seen similar structures come with stamped engineering calcs, but never reviewed any of them.

The original question was what to call it. Whatever it is, it contains the word "semi" no less than 3 times. Such as "semi-fixed, semi-connected, semi-magic ridge connection".

 

[phamENG]

This is a bit of a tangent, but on the topic of "pre-engineer building terminology"...do we have pre-engineered buildings anymore outside of these little mass-produced sheds?

A lot of people still refer to them as "PEMBs"...but I always took the "pre-engineering" to mean they were stock designs that resided in a book somewhere to be ordered, fabricated, and delivered with minimal fuss and no design process to speak of. Same with "pre-engineered trusses"...when they started there was a book of allowable spans for certain trusses. It wasn't economical to design these for every building, so they had standard designs that the factories were tooled to produce and they really didn't get changed.

Today, they're all custom designed. Even if it's "standard" it still gets plugged into the software and you get a custom print out for your fabrication and erection drawings and the calc package. So it's not really "pre-engineered" anymore...it's just engineered on demand. By creating special design packages and limiting options (in some cases - metal building systems are getting pretty flashy) they can still maintain a minimal design process that conveniently ignores everyone else involved and assumes they'll all fall in line.

 

[Ron247]

phamEng, that is my definition of a PEMB also. It is like buying clothes. Give me a 42 regular. I think the smaller mom and pop metal building companies still try to do it that way. The larger ones are frame design per order. This is especially true since codes have evolved so much over the years as compared to when those stock designs were originally done.

To my knowledge, all buildings are engineered before they are built so they are all Pre-Engineered but not in the sense we are talking about in the PEMB world.