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cold formed shed V's the engineer

RE: cold formed shed V's the engineer

Sounds like these shed engineers are getting more clever all the time.

RE: cold formed shed V's the engineer

It's crudely put, but I also wonder how some of those sheds would work.
I don't think that I could prove adequacy by calculation.

RE: cold formed shed V's the engineer

Run it in a program like space gass, makes the job of verifying the design easy. Technology is the main reason we design better and more economically, the laws of physics have not changed..

I like the way they say it all boils down to luck..that is reassuring. No one would use these in cyclonic regions anyway, plus the chances of actually reaching 50m/s is slim.

There is no 'trick' to good design, fabrication and installation.

RE: cold formed shed V's the engineer

(OP)
Engaddict,
Hate to burst your bubble, but these shed are built in the tropics all the time, when cyclone harry crossed the cost, the rate of fail of these sheds was four times that of any other sector, the next being old houses (not designed for the wind speed). Of the engineer products, they had an 80% greater failure rate, and Larry wasn't even a design event.
From what I have reviewed of these designs, there are a few ways the engineer justifies his design.

1.    Takes moment into the base fixing, however most of these are fixed to the concrete with an angle and chemical anchors, thus rotation requirements are way too high to be considered a moment carrying connection, before failure of the frame.

2.    Use the sheeting for bracing in both directions, most of the time assumed not backed up by calculations or testing.
 
3.    Catenary Action for the design for purlins, I don't know how people think this one works but hey why not, once you have made all the other assumptions.

4.    Ignore internal pressure in region c however do not design the roller door or stays to take the wind design. The big thing here is that engineers in this area are using cold formed C's as the door mullion. Then relying on the catenary action of the roller door, however the C-sections have no real strength in torsion, so it all goes up the creek without a paddle.

Generally form my experience you can tune a design by about 5% more from hand cal's to computer. Anything greater than this is BS or the hand cal's were overly conservative.

This article is a true representation of how a small group of engineers have let down the profession and the community.  

Arguing with an engineer is like wrestling with a pig in mud. After a while you realize that they like it

RE: cold formed shed V's the engineer

What bubble?

If they are being used then it is bad design, we design for category D cyclonic conditions all the time and never have any problems.

They should all be pinned connections, and yes, usually hand calcs are more conservative hence they wouldn't have passed in the past.

I agree you can't ignore internal pressure. It is all part of the failure analysis.

Only hollow sections are any good for torsion but doesn't mean C sections can't be used. They must take it into the design, ensure full moment connections for the pre-fabricated modules.

You can use sheeting for strength (I wouldn't for this type of design) but you must perform FE analysis for any conclusive results.

It doesn't appear that the article was written by an engineer. Don't think they have any engineers on staff, sounds more like is was sub-contracted to an engineering firm and then they paraphrased their design recommendations to suit their article.

RE: cold formed shed V's the engineer

The only time I have used sheeting in strength calculations is for restraining cold-formed C/Z sections for flexural-torsional buckling.

I think it would be unethical to use sheeting in any other calculation.

 

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